Why Isn’t My Urethane Plastic Part Curing?

If you’ve ever used urethane plastic for your part-making or prototyping projects and it won’t dry or cure, VFI has answers for you. From experience, we know this issue typically occurs in the application process when the chemical reaction between the liquid components fails to take place or does not occur correctly. Curing can be affected by improper mixing, cold temperatures, thin pours, and incompatible additives.

Every urethane plastic material will come with its own cure timeline. Depending on the formula, it can happen as quickly as 5 minutes or as slowly as 48 hours. Always refer to the manufacturer’s technical data sheet for product-specific instructions when curing and post-curing.

Reasons Urethane Plastic Will Not Cure

1. Incorrect Mix Ratio & Poor Mixing

Since thermoset polyurethane plastics are two-component materials, they must be measured using the correct ratio by weight or volume and mixed thoroughly. If you deviate from these ratios or do not mix it well enough, it may not have the materials to cure. These mistakes can happen because users rush to use the material before the working time ends.

Other factors that can influence off-ratio measurements and poor mixes include:

• Material separation. If your material has been stored for a while and you don’t premix it before combining the components, you might run into curing issues from separated ingredients.
• Bad weight scale. If you’re using a scale that isn’t 100% accurate, you may be measuring too much or not enough of each material, which can cause issues with curing.
• Bad dispensing equipment. Instead of pouring the material by hand, some part makers use dispensing equipment. If the dispensing equipment gets off ratio from blocked lines or an off-ratio pump, it can result in an improper cure.

If you undermix or don’t mix for long enough, it may result in a sticky or warped part. This usually occurs by not scraping the sides and bottom of the mixing container. If sticky residue is on your tooling material, it can be hard to remove, which prevents the tooling from being used for future castings. In some cases, improper mixing can even prevent the part from being able to accept paint.

If you don’t use the correct mix ratio, your part may leach or exude oil in certain spots once cured. This typically happens from using too much of the B (POLY) component. You can also tell if your “cured” part is heavy on the A (ISO) or B side because it will appear streaky or non-uniform in color. Some liquid components will be similar colors, so it’s not always easy to tell if the mix is uniform before cure.

Off-ratio mixes and poor mixing can also affect the final properties of the part. Typically, parts will not meet their designated Shore hardness level or provide the same durability specified on the technical data sheet.

2. Cold Temperatures

Cool and freezing temperatures slow down the curing process and can even inhibit the cure of some polyurethanes. Various elements in the part-making process can be influenced by these conditions.

• Tooling. If the tooling you’re using to cast your urethane part into is too cold, it could affect the material as it tries to cure. The heat the material generates might not be enough to elicit the curing reaction. Some manufacturers recommend using heated tooling, while others recommend at least a standard room temperature.
• Environment. If your workspace has low temperatures or your part is left in freezing conditions, it might not cure. While the part creates a heat reaction, it might not be able to warm up enough if ambient temperatures are too low.
• Material. If the material freezes in transit or storage, the ingredients in the B component may separate. If the separated material is combined with the A component, it might not cure properly, and once cured, it may exude an oily substance.

3. Pouring Too Thin

Most urethane plastics have a thickness minimum requirement of ¼ or ½ inch. A few products can go as thin as 1/8 of an inch. However, the thinner the pour, the longer it will take to cure. Extremely thin parts don’t create the heat necessary to fully cure, especially if tooling and ambient temperatures are not elevated. These parts will need to be post-cured in an oven to generate the heat reaction. Depending on the thickness, additional heat might not always work. Avoid working with small batches of material, as this can also inhibit curing.

4. Incompatible Additives

Certain wet foreign materials added to a urethane plastic may be incompatible with the mix and affect curing time or final properties. Some pigments and fillers can cause the resin to cure too soft, while others will make the part feel oily because the pigment is leaching out. Incorporating too much of these additives can also affect the mix ratio, resulting in a failed cure.

Solutions

Warm both components to at least 65°F before use and work in a room-temperature environment (77°F) with low humidity. Premixing the B component is typically recommended to re-blend ingredients where separation may have occurred.

Use the correct amounts of A and B side components as specified on the technical data sheet. If you’re measuring by weight, use an accurate gram scale. We recommend this method for the most accurate results. If you’re measuring by volume, ensure your mixing cups are accurately marked and you’re filling to the correct line. Spring scales and some graduate mixing cups should be avoided as they only offer approximates.

Thoroughly mix your materials together. Use clean, straight-sided mixing containers with flat bottoms and straight stir sticks or power mixing equipment. Scrape the sides and bottom of the mixing containers so material is distributed evenly. Be conscious of your working time, but if you have enough time, pour your liquid plastic into a clean mixing container and mix again to ensure uniformity.

When adding pigments or fillers to your plastic part, use compatible, chemically dry materials, and do not overuse them.

Before pouring or injecting your material, you might want to heat your tooling material in an oven to ensure the part cures properly. This process can also help dissipate bubbles generated in the mixing and pouring process. Only heat tooling if it is recommended by the manufacturer.

Ensure you pour the part thick enough as specified by the manufacturer’s instructions. Avoid pouring any material under 1/8 of an inch. Thinner materials will take longer to cure since they generate less heat and typically need to be post-cured.

Understand the curing stages of urethane. Some urethanes require a longer time to cure due to extended pot life or other factors. Most urethanes at room temperature won’t develop full properties for 3 to 7 days. Some resins recommend and even require post-curing in an oven for several hours at temperatures as high as 170°F to achieve full physical properties. If you do not follow the manufacturer’s instructions, your part might be weaker than anticipated and may never fully cure.

Contact VFI if you have any further questions when using urethane plastic for part-making applications.

Qwik Spray vs High Pressure Spray for Truck Bedliner: Which to Use?

VFI offers several products to accommodate the application of spray-on truck bedliner. The two methods most utilized are Qwik Spray and high-pressure. These types of spray equipment are vastly different from each other, so do you know which is best for your autobody shop?

Cartridges are an inexpensive way to enter the bedliner industry, especially if you’re only planning on spraying at lower volumes or providing patch repairs.

High pressure bedliner is better for autobody shops spraying consistently at mid to high volumes. This is more so due to the upkeep associated with the equipment.

VFI has put together this guide to help bedliner applicators weigh the pros and cons of these polyurea hybrid products and the associated spray equipment.

Note: You will need a designated spray booth for proper ventilation. Always wear personal protective equipment, such as an approved respirator, when spraying.

Qwik Spray Gun & Requirements

The recommended applicator for this spray method is the VFI-7500 Qwik Spray Gun with GS-15 Static Mix Tips. Cartridge-based equipment like this utilizes air to atomize the material. Air compressor requirements to run the Qwik Spray Gun are dry air capable of supplying 10 cubic feet per minute (CFM) at 100 pounds per square inch (PSI) minimum.

The trigger on the Qwik Spray Gun uses a continuous flow and should not be stopped once pressed. If you stop, the material will cure in the static mix tip, and you’ll have to swap tips before restarting.

VFI’s cartridge-based bedliner is VFI-544 Qwik Spray Bedliner.

High Pressure Spray Rigs & Requirements

Recommended rigs for this spray method are plural component Graco air, electric, or hydraulic sprayers that can accommodate temperature and pressure recommendations. High pressure rigs utilize heat and pressure to produce a fine, even texture. The equipment should be able to provide a minimum of 2,000 psi of constant pressure at 150-155°F.

High pressure guns have a controlled trigger, which can be released during application. You do not need to spray constantly, as the material mixes right before it leaves the spray gun.

VFI’s high pressure bedliner is VFI-542 High Pressure Spray Bedliner.

Qwik Spray vs High Pressure Material Properties

Cartridge-Based Spraying Advantages

1. Portable

As long as you have an adequate air compressor and the lightweight applicator, you should be able to take your bedliner on the go if you don’t plan to only spray at your shop. High-pressure equipment is heavy, and most rigs can’t be transported easily, so cartridges are a great alternative. Note: Portability will also depend on the size of your air compressor.

2. Cost-Effective for Limited Spraying

If you’re looking to have bedliner application as an additional service to your autobody shop, you’ll probably be more interested in Qwik Spray equipment. It’s a great addition to your offerings if you’ll only be spraying a few truck beds per month.

The initial startup costs of the Qwik Spray Gun are much lower than if you were to work with a high-pressure rig. While the material might cost more, you won’t have to justify the equipment costs if you’re not spraying consistently. Typically, a single case (6 cartridges) covers an entire truck bed.

This spray method also reduces labor costs because there’s less setup and cleanup. With the two components already pre-measured in the cartridges, you don’t have to worry about pre-mixing materials, checking for correct mix ratios, etc. All you need to do is make sure the rest of the truck is taped up and covered to protect it from overspray.

If your spray load increases substantially, you may then consider upgrading to high pressure equipment to save on material costs. A cartridge kit is just under a gallon of material and is more expensive than purchasing gallons or drums.

3. Limited Training Needed

Before cartridge-based bedliners were created, you had to have specialized training and knowledge to use high pressure machines effectively. Now, the material is more accessible with this user-friendly application method.

VFI’s Qwik Spray applicator is easy to use from start to finish, with minimal training necessary. We even offer a guide with pictures on how to use the Qwik Spray System. With a built-in airflow regulator, you’re also able to easily adjust the flow and pattern you desire while spraying.

Note: New bedliner applicators will need to practice to achieve a consistent, textured finish.

4. Reduced Equipment Maintenance & Easier Cleanup

With the Qwik Spray applicator, you have few replacement parts to worry about if the gun breaks down. It has no hoses, fittings, pumps, or other expensive machine parts like a high-pressure system has.

Disposable cartridges and static mix tips also make cleanup much easier. You don’t have to worry about flushing spray lines with solvents or doing regular maintenance on your rig to prevent downtime. If you’re not constantly spraying or cleaning the machine enough, old material can clog up the lines as well.

5. Improved Non-Slip Protection

The VFI-544 Qwik Spray Bedliner is a bit softer than its high-pressure counterpart, which gives it a bit more grip. Because cartridge-based bedliners spray at a lower pressure, a less fine texture is produced, which creates a better skid- and slip-resistant surface. If you need the bedliner to have these features, the Qwik Spray Gun might be a better option.

High Pressure Spraying Advantages

1. Best for High Project Volume

If your autobody shop has enough business where you’ll be spraying truck beds consistently, high pressure is more cost-effective in the long run. It has a higher initial investment due to equipment costs, but high-volume spraying should help you make that back quickly. Drums and tote prices are typically more affordable due to the way the material is packaged vs cartridges.

High pressure equipment also has to be used regularly for maintenance purposes. If you’re spraying almost every day or a few times a week, you shouldn’t have to worry. If you do not have plans to use your high-pressure rig for an extended period, make sure to flush the lines to prevent bedliner buildup.

2. Allows for Versatile Material Options & Applications

Premium bedliner options like polyurea coatings are available for high pressure spray equipment. The VFI-200, VFI-201, or VFI-202 50 D Polyurea Coatings are recommended if you want a higher-end bedliner. However, polyurea hybrid coatings work just as well and can be sprayed in a high pressure and cartridge format.

You’re also not limited to spraying truck beds. If you need to make the cost of the equipment worth your while, you can spray different parts of the vehicle or other recreational vehicles like ATVs, boats, side-by-sides, and even utility trailers, ramps, work trucks, etc. We’ve also provided these products to users with vastly different applications like tank pads, table edging, and speaker boxes.

3. Better Control When Spraying

Because you don’t need to constantly hold onto the trigger while spraying, you can control how and where you spray. This makes it easier to get a consistent thickness across the board, as well as a desirable, uniform texture for the final finish.

High-pressure creates a very fine texture, which is much nicer than some low-pressure options. Because cartridge-based coatings utilize lower pressure and no heat, they produce a less fine texture. If texture matters, this may be something to consider when choosing equipment and materials.

You’ll also save material with high pressure because you can stop at any time once you’ve completely coated the truck bed and reached a desirable thickness. The spray equipment only mixes what you need, so you can store leftover material with a nitrogen purge once you’re finished. Most truck beds utilize 2-3 gallons of material, depending on the size of the truck.

4. Higher durability

Because the VFI-542 High Pressure Bedliner has higher tensile and tear strength as well as higher hardness, it is more resistant to physical damage, wear, and tear. This makes it durable and reduces the amount of chips, scratches, and dents over time. It is also less susceptible to the effects of temperature changes.

5. Good for On-Site Spraying

For the most part, bedliner is typically sprayed in a consistent location. There’s not usually a reason to go somewhere else to spray unless that’s a service you would like to offer. So, if portability isn’t desirable to you, look into a high pressure rig.

Regardless of the equipment you choose, both coatings provide similar, durable protection for truck beds.

Contact VFI if you need further assistance choosing the right bedliner and equipment. We also have a separate low-pressure version, primer, and UV-stable top coat to round out your line.

What’s the Difference Between Advanced Detail & Simple Formliners?

The main difference between advanced detail and simple concrete formliners is the complexity and depth of the design they can produce. Advanced detail formliners replicate intricate and custom designs, while simple formliners produce basic textures and patterns.

The form liner’s ability to create details is typically affected by the material used. Some materials can transfer and produce higher detail than others without wearing or tearing.

The material most commonly used for detailed and even simple projects is polyurethane. However, there are many urethane rubber options to choose from. Your project needs will determine the exact material that will work best.

How to Choose the Best Form Liner Material

The purpose of a formliner is to transfer a desired amount of texture or pattern onto concrete. The type of urethane rubber you use for your formliner will depend on your aesthetic goals, reuse needs, budget, and project size.

Why Does Hardness Matter?

The properties of urethane rubber will be a factor in which material will work best for your project. Shore hardness is an important property to note. It quite literally determines how hard the material is. It also tells you about the flexibility of the material. Urethane rubber with a Shore hardness of 90 A will be more rigid and less flexible than rubber with a 25 A hardness.

Formliners typically require a special combination of flexibility and rigidity. Most formliners range between 60 A and 90 A in order to optimize the properties to the liner.

What Level of Detail Do You Require?

If you need high-quality finishes and intricate designs on your concrete, rubbers with more flexibility and lower hardness should be your go-to for making formliners. A medium-hard rubber will have a better time replicating an original’s details than a very rigid rubber.

For advanced detail, VFI recommends using a rubber between 60 A and 70 A. It is at these hardnesses that the rubber will have the flexibility needed to release from decorative pieces more easily. These details can include customized logos, shapes, or three-dimensional effects that create a distinct identity or theme.

If you’re working on a less detailed project, your liner might need to be more durable. You would probably want to use a harder rubber for increased strength. VFI recommends using a rubber with a Shore hardness between 70 and 90 A if detail is less important.

Rigid rubbers are at a greater risk of not demolding or breaking the concrete because of their limited flexibility. That’s why it’s better to use these materials when your design is more subtle and less pronounced, with few undercuts.

Basic textures and patterns can include masonry appearances such as brick, stone, and wood. Even though these liners are simple, they will produce more natural results than if you were to use a material like plastic.

How Many Pulls Do You Need from a Single Liner?

You should also consider whether you need a liner for a one-time use or if you will need it for other projects down the line. Urethane rubber is desirable due to its high reuse potential. Plastics like ABS or polystyrene can make good simple formliners, but they don’t have the same reuse potential. They will also need to be fixed or adhered to the deck in order to generate a piece, creating more work.

Reuse will depend on the thickness of the liner and how deep the texture is. If you need your formliner to be more durable, you’ll want to consider making a simple formliner. At high hardnesses, these liners are rigid and abrasion-resistant, so they can endure multiple uses. If properly cared for, they can get up to 100 pulls. This can lead to lower overall costs, especially for large projects using a consistent pattern.

Even at lower durometers, you can still get a good amount of pulls from a single urethane form liner. However, some details may wear faster after each use compared to higher durometer urethane liners with simple details.

What’s the Budget of Your Project?

It’s also important to choose a formliner type that best fits your budget. Many people go for plastic formliners because they are relatively low in cost. However, they won’t be as durable if you need to get multiple uses out of them. They also have limited design options for some projects.

If you want a material that’s more cost-effective in the long run and you do not have strict design requirements, you’ll probably want to go with simple formliners made of urethane rubber. Due to their reusability, they work for large projects or multiple projects without wearing down quickly.

More detailed liners may cost more to make due to thickness requirements. They are more cost-effective and desirable for smaller projects because of this. The more detail you need, the thicker the liner will have to be. This is so the liner will have enough rigidity to resist tearing when demolding from deep undercuts.

What’s the Size of Your Project?

A factor that fits in with budget is the project size. If you’re working on a small, custom project, consider using advanced detail liners. The intricate designs they impart can be a good focal point if you’re trying to draw attention to a unique concrete element. They can also produce deep relief patterns while replicating surface textures.

Larger projects, on the other hand, may benefit more from simple formliners. Suitable projects include tilt-up panels, architectural walls, highway walls, bridges, and sound barriers. It is easier and cost-effective to create a long, repeated pattern using several high-durometer urethane liners. These simple form liners will have the strength to withstand the abrasive properties of concrete throughout the entire project. This will help ensure that all sections of the project have consistent details and textures.

VFI Recommended Formliner Materials

If you are in need of an advanced detail formliner material, we recommend:

• VFI-2163 60 A TDI Molding Rubber
• VFI-2165 65 A TDI Molding Rubber
• VFI-2170 70 A TDI Molding Rubber

If you are in need of a simple formliner material, we recommend:

• VFI-2170 70 A TDI Molding Rubber
• VFI-3171 70 A MDI Molding Rubber
• VFI-2180 80 A TDI Molding Rubber
• VFI-3181 80 A MDI Molding Rubber
• VFI-2190 90 A TDI Molding Rubber

MDI urethane rubbers have better adhesion compared to TDIs. This is good for adhering the liner to a rigid backing material like wood. The adhesion is especially desirable for large formliners that can’t be handled without the use of special equipment like cranes.

Contact VFI if you’re still unsure what material will work best for your formliner project.

Why Does My Urethane Plastic Have Bubbles?

When making industrial or prototyping parts out of thermoset urethane plastic, the last thing you want to see in your casting is bubbles. For some applications, like clear, see-through parts, having no bubbles is critical. Not only are they an aesthetic problem, but they can also affect the integrity and performance of the part. The most prevalent reason a part develops bubbles is due to moisture sensitivity.

Other non-moisture-related issues include extreme temperatures, excessive mold release, application techniques, and tooling shape. It wastes time, money, and materials when you have to scrap the part and make a new one. However, if you follow the manufacturer’s instructions, you should be able to avoid these problems and produce bubble-free castings.

Reasons Bubbles Form in Urethane Plastic

1. Moisture

Urethane is a moisture-sensitive material. This means that when it comes into contact with moisture, it will react, resulting in bubbles or foaming. The following elements can all lead to moisture issues:

• Environment. The most obvious source of moisture comes from humidity. If the plastic has a long enough pot life to react with the moisture in the air, bubbles will form.
• Mixing equipment. Bubbles can form when mixing the material if you use mixing equipment that absorbs and holds moisture, like wood or paper. The moisture can then transfer into the urethane.
• Release Agents. Using a water-based release with a urethane plastic will cause a reaction that produces bubbles.
• Mechanical equipment. To remove bubbles with specialized equipment like a vacuum chamber or pressure pot, they must be hooked up to an air compressor line or a vacuum pump. If moisture enters these lines, it will react with the resin and affect the equipment’s ability to remove bubbles.
• Casting surface. If your tooling material is wet for any reason, maybe from cleaning it, it may cause bubbles to form on the face of your part. A tooling material like silicone that hasn’t fully cured before you cast into it can also produce bubbles.
• Open containers. The more you open the A and B side materials, the more likely it is that moisture will be introduced into the mix when they are not sealed. If you don’t use the entirety of both materials, especially on a humid day, you should expect bubbling.
• Wet foreign material. Adding an additional component to the system such as pigment, thickeners, or other foreign materials can cause foaming because of entrapped moisture within the product.

2. Extreme Temperatures

When casting urethane plastic, ambient, material, and surface temperature play a role in the speed of its cure. If bubbles are unable to reach the surface before cure, they will be trapped in the plastic.

Extremely cold temperatures can slow curing or prevent a full cure. Extremely warm temperatures can cause rapid cure, which doesn’t allow much time for the material to release bubbles.

Temperature also affects the material’s viscosity, which affects its ability to release bubbles. Cold temperatures increase the viscosity, and warm temperatures decrease the viscosity. The thicker the material, the slower it will eliminate bubbles.

Thick liquid plastic materials with short pot lives will have a harder time releasing air bubbles at high temperatures. Liquid plastics with long pot lives and high viscosities should be able to release most bubbles at room temperature (77°F). Low-viscosity materials with long pot lives should have no problem releasing air bubbles at room temperature or higher.

3. Excessive Release

Depending on the tooling material you use to cast your urethane plastic, you’ll probably need to use release. Be sure you’re using the right amount of release; otherwise, it could cause problems for your cast part. Excessive application on a surface that is not allowed to dry before casting will cause small pinholes or champagne bubbles on the face of your part.

4. Pouring & Mixing Technique

Poor application techniques can lead to various surface defects. For starters, the way you mix can cause issues. Because these are two-component materials, they must be mixed to generate a chemical reaction. If you rapidly mix the material, you can introduce air into your mix and cause bubbles.

Even the way you pour your material into your mold can create air bubbles. Pouring too quickly and moving around as you pour doesn’t allow trapped air to escape as easily.

5. Tooling Shape

Removing bubbles can be difficult if the tool you’re casting into has complex details or undercuts. Some undercuts can trap air when the material is poured. The air may not be able to rise to the surface and escape fast enough before it starts to cure. This will cause large surface bubbles that are unacceptable for certain parts.

Also, if you’re product thick parts, trapped air might take longer to rise in the mold, especially if it has a high viscosity.

Solutions

Follow the manufacturer’s recommendations for temperature and humidity. Room temperature (77°F) allows most materials to maintain a workable viscosity. This makes it easier to mix and less likely to trap air. Also, ensure your workspace and equipment are dry, especially during the application process.

Warming your material to at least 65°F can also help lower its viscosity and allow air to escape more easily. Warming the tooling material or making sure you are not casting onto a cold surface can also prevent bubbles. Be aware that warmer conditions will result in a reduced pot life.

To prevent the urethane part from adhering to your tool, you’ll need to use a compatible, non-water-based release. Don’t overdo it on the mold release, and allow the release to dry before casting to prevent bubbles.

Mix the two components slowly, consistently, and thoroughly. The best mixing equipment you can use, especially for large amounts of material, is a paddle mixer attached to a drill. This equipment can reduce the amount of air that is introduced while you are mixing. It mixes the entire container, including the corners and bottom. Also, when adding any foreign material to the plastic, make sure it is chemically dry with the lowest moisture content possible to avoid incorporating trapped air.

Even with good mixing techniques, it’s likely that some air will be introduced into the material. During the pouring process, you want to pour slowly, in one place, and allow the material to flow into the mold. Pouring in a high, thin stream can help to minimize air bubbles as well.

The two most effective ways to get rid of bubbles in your urethane parts are:

• Vacuum degassing is a method of removing bubbles before you pour the resin into the tooling material. The vacuum chamber sucks out all the trapped air, making the material rise and then collapse as it is removed.
• Pressure potting is a method to force material into the face of the tooling to remove any imperfections caused by the surface or bubbles. The part will cure fully in the pressure chamber giving a consistent finish. Note: your tooling material should be made under the same pressure to avoid distortion.

For our VFI-4500 UV Stable Clear Polyurethane series, these methods are required to get rid of bubbles for a crystal-clear part. Other plastics, like VFI-110 75 D Injectable Plastic or VFI-1678 80 D Injectable Plastic, are too hard to vacuum degas due to their short pot life. However, because they are injectable and do not incorporate air, they fill the mold quickly with little to no air entrapment.

If you don’t fully use your material, put the container lids back on as soon as possible. Make sure to store them in a temperature-controlled, dry location. You can nitrogen purge both sides to extend the shelf life as well. However, the pot life will be greatly reduced once they are open.

If none of these methods work, use a different material. You might not have chosen the best urethane for your project. If getting a bubble-free cast is crucial, consider finding a low-viscosity material with a long enough pot life that provides ample time for bubbles to rise and escape naturally or through mechanical means.

Contact VFI if you are having other issues when casting urethane plastics.

How To Determine Coverage Rates for Coating Projects

Before applying a protective coating, the most important thing to consider is how much material you will need. Knowing this amount will also help you determine the potential cost of a coating project. There are four main factors you will need to consider to determine this:

• How big is the area you need to cover / how big is the project?
  • The area is typically determined by calculating square footage (length x width).
  • If you are working with a rougher surface, you may need more coating.
• How are you applying the coating?
  • Spraying versus rolling or brushing the coating onto the surface can affect how much material you need. Rolling and brushing techniques usually require more coating due to waste generated during the mixing, pouring, and application process.
• How thick do you need the coating to be for optimal protection?
  • All coatings vary in terms of thickness requirements. These requirements can be found on the technical data sheet. There is a minimum amount recommended to create uniform coverage that will protect the surface or project. The thicker you apply the coating, the more you’ll need.
• What is the solids content of the coating?
  • Solids content is the amount of potential solvents in a coating that will evaporate while it cures. So, the wet film thickness will differ from the dry film thickness.
  • For coatings that are 100% solids, you don’t have to worry about volatile content or low solids content affecting the dry film thickness. In other words, the amount you apply is the amount that will remain on the surface. Most of VFI’s industrial coatings and hard coats have a 100% solids content, so this is not a concern when determining the material needed.

Why Coating Thickness Is Important & How to Measure

Coating thickness directly affects the durability and performance of the coating. Ensuring you apply enough material will allow the coating to provide an effective protective barrier. Coatings like urethanes, polyureas, and hybrids can provide resistance to corrosion, weathering, abrasion, and chemicals.

Most manufacturers list coating thickness in mils. Some applicators might be unfamiliar with the term. A mil is defined as one-thousandth of an inch. Coating thickness is expressed this way because these materials are applied thin (under a quarter of an inch or 250 mils). Film thickness can be measured before the coating has cured with a mil gauge.

One gallon of a 100% solids coating applied at one mil will cover 1604 square feet. Knowing how many square feet a single mil covers can aid in the process of determining how many gallons you need to cover a specific area at a specific mil thickness. Knowing the coating thickness helps you control costs while ensuring adequate coverage.

All VFI coatings specify thickness requirements on each technical data sheet. Follow these specifications to create a durable layer with good physical properties to protect various surfaces. You will also need to know your desired mil thickness to help calculate how much material you will need.

What Happens with Improper Coating Thickness?

If you are not applying the recommended amount of a coating as specified by the manufacturer, it can affect several properties and the material’s ability to form a proper protective surface. Following the manufacturer’s instructions can help you avoid various issues, including coating failure. The application should be consistent and uniform across the entire surface for the best results.

Inadequate coating application can result in:

• Property Reduction – A thinner coating may not be able to reach its full properties and will affect the cure speed.
• Adhesion issues – The coating needs to be applied thick enough to develop a bond with the surface. If the bond fails, the coating might peel, crack, or delaminate over time.
• Surface defects – Insufficient coating thickness can create small voids or pinholes on the surface.
• Project delays – If you run out of material before you’re finished with the application, needing to get more will cause delays.

Excessive coating application can result in:

• Sagging – Applying a lot of material, especially over vertical surfaces, can cause sagging. The coating will settle unevenly and be thicker in certain spots.
• Cracking – If the coating is too thick, temperature fluctuations or stress can make it more prone to cracking.
• Shorter cure – The cure time of most coatings is tested at a standard mil thickness. Excessively applying the coating can shorten the cure time, resulting in reduced recoat window and adhesion issues.
• Material waste – If you apply more material than you truly need, you’re wasting material you could use for a different project and increasing expenses.

How to Calculate Coating Coverage

When calculating the material you need, it will be an estimate, as various factors could affect the actual amount required. You’ll first need to know the surface area you need to cover. We recommend finding the square footage, which can be determined through the simple math formula length x width.

• Formula: L x W = Area (Square Footage)

The most common formula used to calculate the application rate per gallon is dividing the square footage per gallon of a single mil by the desired dry mil thickness.

• Formula: 1604 sq. ft. per gallon / desired mil thickness = coverage (sq. ft.) per gallon

Ex.) A manufacturer requires a coating to be applied at a minimum mil thickness of 40. To determine how many square feet the coating would cover at this thickness, you would use the following equation:

• 1604 sq. ft. per gallon / 40 dry mils = 40.1 sq. ft. per gallon

Now, let’s say you determined that you have 100 square feet (10 ft x 10 ft) to cover at 40 dry mils. You would divide the project square footage by the square footage the desired mil thickness covers to get the minimum number of gallons required.

• 100 sq. ft. per gallon / 40.1 sq. ft. per gallon = 2.49 gallons

You would then round that to a whole number (3 gallons). Because VFI’s coatings come in 1-gallon kits, 5-gallon kits, drums, or totes, we’d recommend a 5-gallon kit of material for this project to account for potential waste.

Accounting for Waste

An estimate does not account for surface texture, overspray, spills, equipment problems, or application methods. It’s always a good idea to add 10-15% of material to your calculations to account for shortages that would otherwise cost you time and money.

Coating Coverage Chart by Mil Recommendations

VFI typically does not recommend using any of our coatings, whether that be industrial coatings, bedliners, or hard coats, under 30 mils. Please read the technical data sheet associated with the product for thickness requirements before application.

Contact VFI if you have more questions about coating application or thickness requirements.

Why Is My EPS Foam Bending After Applying a Hard Coat?

If you’re working with long, thin EPS boards and urethane hard coats for your theming project, you should be aware of issues that can occur during the application and cure process. Foam boards of this size and thickness or at lower densities have a limited ability to resist bending or warping after they have been coated. This typically occurs when the material is applied too thick in a single pass.

Why Hard Coat Thickness Matters

Thickness directly impacts the coating’s appearance, performance, and durability. All urethane hard coat products come with a recommended application thickness rate for proper coverage and to extend the life of the EPS piece. Due to the different ways hard coatings are applied, the achievable thickness and uniformity may be different for a brushable hard coat vs a high-pressure or Qwik Spray application.

The viscosity of the material can also play a role in the final thickness of the coating. Higher-viscosity materials, like brushable coatings, will generate a thicker film build, while lower-viscosity materials, like sprayable coatings, will generate thinner builds. Brushable coatings can make applying an even amount of coating more difficult, which can cause more tension on one end of the foam piece and result in uneven curling.

It’s important to spray enough of the coating to protect your piece, but there is a certain point where too much coating can affect the surface below. Some applications require the coating to be applied very thick (up to 250 mils) for increased protection. If you apply it that thick in a single pass, it will cause issues for your piece.

As polyurethane hardens, the chemical reaction generates heat, with temperatures getting as high as 175°F. While curing, the coating experiences some degree of shrinkage, which creates tension on the surface of the foam. The more material you apply, the hotter the coating will get as it dries, and the more it will shrink. The coating will pull the foam out of shape and permanently bend or curl it. Thinner sheets and lower densities of EPS bend because they have less rigidity and will respond to this stress.

Note: Applying too much hard coat at once can also lead to sagging or wrinkling of the coating and even difficulty drying or curing properly. Excessively thick layers will be even more prone to cracking or chipping.

Solutions

Always refer to the technical data sheet of the product for thickness requirements and application techniques. To prevent your foam pieces from bending, you’re going to want to spray or brush on the coating in multiple thinner passes. Several even layers are always better than fewer heavy ones. This will prevent the heat generated in the curing process from adding stress and shrinking the foam.

VFI’s recommended thickness ranges per product are:

• VFI-2519 75 D Brushable Hard Coat and VFI-2626 65 D Brushable Hard Coat: Apply a minimum of 60 mils to create a uniform film on the piece. For the best performance, they should be applied at 100 mils or more. You can build up to this thickness in 2-3 coats.
• VFI-6170 70 D Spray Hard Coat and VFI-6171 Qwik Spray Hard Coat: Apply between 40-80 mils to create a uniform film on the piece. For increased impact resistance and outdoor applications, they should be applied between 60-120 mils. You can build up to this thickness in 2-3 coats.

You can add as many coats as you want as long as the previous coat has set up and the recoat window has not ended. If you miss the recoat window, lightly sand the surface before applying the next coat or use a compatible primer. Doing so will help ensure intercoat adhesion.

Alternatively, you could encapsulate the piece to balance the stress the coating application creates. After spraying the top of the piece, allow it to cure before flipping it over to the other side and spraying so there is a similar opposing force to straighten it out.

If you don’t need to work with flat, thin pieces, we recommend spraying 3D objects or thicker boards that are harder to bend. If you must work with large, thinner sheets of foam, consider reinforcing the foam with a rigid backing material first or increasing the density of your foam.

Contact VFI if you are still experiencing issues with your EPS hard coat, including bubbling, curing, or failure problems.

Understanding the Properties of Urethane Plastic

In the part making and prototyping world, understanding the properties of urethane plastic is essential for choosing the best material for a specific application. If you’re new to using thermoset polymers like urethane, you may not know which properties are most important for making plastic parts. The answer will vary based on how you need your parts to perform. This comprehensive guide will lead you through all the essential properties and why you should know them.

What Physical Properties Are Important?

The physical properties of urethane pertain to the material when it is in a cured state. These properties will tell a urethane user how their cast parts will hold up in their desired application. They are tested by manufacturers and third-party laboratories using standard methods from the American Society for Testing and Materials (ASTM). The following are the most popular properties that manufacturers list on their technical data sheets:

Shore Hardness

Test method: ASTM D2240

Definition: Shore hardness indicates a material’s resistance to indentation or deformation. Materials are compared using different scales based on similar characteristics. The higher the number on the scale, the greater the plastic can resist indentation, meaning the part is increasingly harder.

Importance: Shore hardness is a factor that indicates the durability, flexibility, and machinability of urethane plastic. High performance plastics are measured on the D scale from medium hard to extra hard (20 D – 90 D).

A rigid material is typically more durable, abrasion-resistant, and can bear more weight than softer, flexible materials. Many high performance plastics are rated 60 D and above, indicating that they are very tough and resistant to tears with limited flexibility, if any.

These hard plastics are a great choice for making parts that will experience a lot of wear and tear, such as production parts and equipment housings. They are highly suitable for applications where rigidity, wear resistance, and dimensional stability after cure are crucial.

Note: When looking at VFI urethane plastics, you will notice that they all include the Shore hardness in their names to make it easier to find what you’re looking for (i.e., VFI-4170 70 D Fast Casting Plastic).

Tensile Strength

Test method: ASTM D638

Definition: Tensile strength is the maximum load a material can support before it breaks or fractures when stretched. It has also been called a tension or pull test and is expressed in pounds per square inch (psi).

Importance: Parts are often subjected to various types of stress (tension, compression, bending, etc.), so tensile strength is important for determining if a urethane part has the structural integrity and durability to resist tension forces. The ability to sustain higher stress than other materials is one of polyurethane ’s greatest qualities.

A part with high tensile strength can withstand significant loads without breaking. Applications where the material will be subjected to constant stress, such as industrial parts, rotocast parts, and tooling, can benefit from high tensile strength. These parts are less likely to fail, so you can count on them to perform in tough situations. Materials with higher tensile strength also tend to be rated higher on the shore hardness scale.

Tensile Modulus

Test method: ASTM D638

Definition: Tensile modulus is closely associated with tensile strength as it relates to the ratio of tensile stress to strain when a material undergoes deformation when stretched. It is a calculated number that uses the same test method and measurement (psi) as tensile strength since both test tension (pulling) force.

Importance: Tensile modulus is a property that helps you determine how stiff or rigid a urethane plastic part will be under tension. It will also tell how much the part will deform or elongate under that force. A high tensile modulus is great for applications that require high stiffness and minimal deformation to increase the longevity of the part.

When a part has a high tensile modulus, it means it will resist stretching. It has great dimensional stability to maintain its shape under consistent loads. Like tensile strength, it is often associated with hardness. Harder parts may have a higher tensile modulus, though some custom formulas can break this standard.

Flexural Strength

Test method: ASTM D790

Definition: Flexural strength measures the maximum force needed to bend a material until it breaks. Like tensile strength and modulus, it is expressed in pounds per square inch (psi).

Importance: Many applications subject plastic parts to bending forces in everyday use. A part with good flexural strength can handle this stress without snapping, breaking, or warping. Knowing flexural strength will make it much easier to identify if a material is strong enough to resist deformation. High flexural strength parts are durable and will keep their shape and function better for longer. If a material’s flexural strength is on the lower end of the spectrum, it might mean that the material is more brittle. Plastics with higher flexural strength will usually be rated higher on the hardness scale, which helps them resist the bending force.

Flexural Modulus

Test method: ASTM D790

Definition: Flexural modulus measures a material’s stiffness or resistance to a bending action. It uses the same test as flexural strength and is expressed the same (psi). It is different from tensile modulus because it tests a material’s resistance to deformation when bent, whereas tensile modulus tests this resistance when stretched. Both properties, however, indicate a material’s rigidity.

Importance: Flexural modulus is important because many part makers require a certain degree of stiffness in their plastic parts to withstand bending forces. A higher modulus means the material is stiffer and will bend less under a specific load. Understanding this property and how it affects the performance of plastic parts makes it easier to create quality components for high-stress situations.
Parts with a high flexural modulus are also strong and rigid, so they can provide support where needed. Rigid parts are used for applications like automotive parts, gears, furniture pieces, etc.

Shrinkage Linear

Test method: ASTM D2566

Definition: Linear Shrinkage is the change in the length of a material along linear dimensions (length, width, and height) as it cures. The contraction is usually expressed as inches per inch (in/in) and tests a 12 x ½ x ½ sample.

Importance: Part makers should know that urethane plastic shrinks as it cures, which could affect a part’s final dimensions. Most shrinkage will occur when the part is cooling in the mold, and a small amount can occur after demolding.

The rate of shrinkage is dependent on several factors. Some plastic materials might not have thermal properties to withstand shrinkage. Processing conditions like temperature, pressure, and flow rate can increase the shrinkage of a part as it cures. The part size, if you are using a lot of material to make large parts, can also cause shrinkage.

When you know how to work around linear shrinkage, you can maintain consistent part dimensions throughout production runs. If a part is undersized, it might not be able to perform its intended function, which can be a waste of time and materials.

Izod Impact

Test method: ASTM D256

Definition: Izod impact is a test method that measures a material’s toughness or resistance to impact. It is used in the polymer manufacturing industry to determine the toughness of plastics. It is typically measured as the amount of work required (ft-lb) to break the material a certain amount (in). The two ways Izod is tested are:

• Notched: It tests impact resistance from a swinging pendulum with energy focused on a notch. This measures the material’s ability to absorb impact despite having a flaw (the notch). Calculated values are typically lower because a notch is much easier to continue breaking and simulates real-world situations better.
• Unnotched: It tests impact resistance from a swinging pendulum with energy focused on the entire test piece so force is distributed more evenly. There is no premade notch because it measures the material’s overall toughness. Calculated values are typically higher and might not represent real-world situations where imperfections are likely.

Importance: Good impact resistance is essential for plastic parts that might experience sudden force, shock, or blows. It allows part makers to determine which materials will have the necessary toughness needed to create durable, long-lasting parts. Understanding impact resistance can also help prolong the life of your part and prevent it from failing in high-impact scenarios.

A material’s impact resistance can vary based on the type of material, how thick it is, and external conditions. Urethane plastic can be customized with different properties and has the benefit of being as soft or hard as you want it to be. Softer urethane plastics are going to be better for impact resistance.

However, Izod impact is just one property that can tell a user how tough a material is. Other factors that affect the strength of a material include tensile and flexural strength, which may be more important depending on the application.

Heat Deflection Temperature

Test method: ASTM D648-18

Definition: Heat deflection temperature (HDT), also called heat distortion temperature, is a thermal property unique to polymers and plastics. It tests the maximum temperature at which a material deforms under a given load. Depending on the material, it will be tested at 66 psi or 264 psi.

Importance: HDT determines if a plastic part can remain rigid and keep its shape under high temperatures and constant loads. When a part reaches its HDT for an extended time, it will lose its load-bearing capability and may fail. This is why you must look at the HDT if you know you’re making a part that will be exposed to elevated temperatures.

A material’s HDT can be affected by several factors. The longer the material is exposed to heat, the more likely it will deform. If the direct or indirect temperature rises slowly, the material might have a higher HDT. The size and shape of the part can also change the HDT, as the thicker the part, the higher the heat transfer rate.

When urethane plastic has a high HDT, it’s better at retaining its shape and functionality in high-heat applications. Some industries where HDT would be important include packaging components, automotive parts, electronic pieces, and medical devices.

Note: VFI also has plastics with fire-retardant in their formula for part-making in a variety of industries, such as medical, automotive, and aerospace.

Cured Color

Definition: Cured color is the color that a material cures to.

Importance: Cured color can affect your plans when making a urethane plastic part, as it is not the same for every product. Some products have a manufacturer’s standard color, but most come neutral, white, or even UV-stable clear to make them customizable to the user. Neutral-colored plastics allow part makers to paint the cured surface for a production-quality finish. However, painting can be avoided by using dyes and pigments to alter the color. Pigments are added to the polyol (B side) before mixing for more time to achieve the desired color before the pot life begins.

However, cured color may not always be important for an application. If your part is hidden from sight or used as an internal component, you probably don’t need to be concerned about this property or UV stability. Most plastic materials on the market are aromatic, and that is okay for most users. If you need a UV-stable part, you should look for products marketed as UV-stable.

What Liquid Properties Are Important?

While not all companies separate physical properties from liquid properties, VFI does, so you can identify which applies to a material when it’s a liquid and when it’s a solid. The following properties are important to know when working with liquid urethane plastic:

Mix Ratio

Definition: Mix ratio is a property that establishes the exact amount of material to combine to produce a solid final product, such as urethane plastic. This property is reported as a ratio for materials with two or more liquid components that must be mixed together. A mix ratio can be expressed in two ways:

• By volume: Using equal-sized containers or dispensing equipment to measure the exact proportions of two or more components that must be combined. It is not dependent on weight.
• By weight: Using an accurate scale to measure the exact proportions of two or more components that must be combined. It is not dependent on the volume.

Importance: Following the mix ratio of any urethane plastic is crucial because it directly affects the chemical reaction that allows the plastic to cure. The combination of materials will ensure that the plastic will develop strong cross-links that lead to a durable, high-strength part.

If these materials are mixed incorrectly, it can result in an incomplete cure. The plastic might be weak, soft, or sticky and won’t function as needed. In some cases, it may never develop full physical properties. Use the proper mix ratio to be sure your parts produce consistent results from batch to batch and reduce material waste.

Viscosity

Definition: Viscosity is a measure of a fluid’s resistance to flow at room temperature (77°F). Many manufacturers list several viscosities for their materials if they include more than one component (i.e., A side, B side, and mixed). It is expressed in centipoise (cps). For a better understanding of the viscosity of urethane plastic, here is how it typically compares to some household items:

Importance: Viscosity is an important property that impacts how you work with a material and affects some of the cured material’s final characteristics. It helps determine how easy it is to pour the urethane into a mold. A low-viscosity material will have a better time flowing into intricate molds with tight corners for detail reproduction.

Low viscosity urethanes are also less likely to trap air bubbles while curing. As the material flows into a mold, the bubbles dissipate more easily to minimize voids and imperfections in the cured plastic. Not only does the surface finish look better, but fewer voids help the material exhibit better performance characteristics.

For quality assurance, you can vacuum degas and pressure pot materials to reduce air entrapment further. These techniques are essential if you are making clear plastic parts.

Pot Life/Work Time

Definition: Pot life or work time is the time it takes for a material’s viscosity to thicken to a state where it is deemed unworkable. More simply, it is the amount of time you can work with the material before it becomes too thick and begins to cure. This can be expressed in minutes or hours, depending on how fast the material sets at room temperature (77°F).

Importance: Since urethanes are customizable, the pot life can be varied depending on a user’s processing needs. There are unique plastic materials that are extremely fast and can only be worked with for 2 minutes, and there are some materials that have a working time of 2 hours or more.

Pot life can always be affected by the temperature of your material, environment, and mold. If you are working above room temperature, your pot life is guaranteed to decrease, which means you’ll have even less time to work with the material. However, some people are okay with increasing the temperature as this can also decrease the time it takes for the part to be ready to demold.

Depending on how big of a part you are making, make sure the material you choose provides enough time to mix, degas, and pour the material. For a material that has an extremely fast pot life, a different casting method is recommended. You will typically not have enough time to mix and pour the liquid before it sets, so injection molding is the processing method that would utilize fast resins.

Gel time

Definition: Gel time is the time it takes a material to stop flowing or become gel-like. It is typically measured in minutes or hours, as it comes shortly after the pot life ends. Like pot life, it is assessed at room temperature (77°F).

Importance: While gel time might not be as important as pot life, it can help you plan your project so you know your workable window. It will also help you avoid mistakes caused by exceeding the workable timeframe and prevent you from wasting material.

Demold time

Definition: Demold time is the time a casting should be allowed to cure before removing it from a mold. It is usually expressed in minutes or hours, depending on factors like pot life and gel time.

Importance: Your material’s demold time is important for part production. Like pot life, demold time can vary depending on the formula. If you are processing parts that must be ready quickly, you’ll want to find a material with a short demold time. If you need to pour large parts, you’ll need a material with a longer working time, but this will result in a longer demold time.

Something to note about demold time is even if your part is ready to be demolded, it will not have full physical properties. Some plastics are unique and require post-curing in an oven to achieve full physical properties. Heat can help any material obtain its properties faster; otherwise, your parts will take a few extra days to obtain the properties listed on a technical data sheet.

Where to Find Material Properties?

It is very important that material properties are correctly listed so that users can trust the material will perform as expected. Our on-site lab uses various standard ASTM test methods to determine the unique properties of each material. Once they have been reviewed thoroughly, we post them on all our product pages and the technical data sheet for each product. Technical data sheets can be found on any product page under resources.

When to Use Silicone vs Urethane Rubber for Decorative Concrete

Knowing which liquid rubber is right for your decorative concrete project can be tricky since there are many factors to consider. Silicone and urethane are the best rubbers for these applications because of their durability, minimal shrinkage, and easy processing. Plus, they reproduce extreme details and textures, which many other molding materials are not capable of doing.

What Is Liquid Rubber?

Liquid rubbers are synthetic materials that typically come in two parts that will cure at room temperature. After curing, the rubbers will have a specific set of properties based on their formula.

• Polyurethane – There are two types of urethanes for mold making: TDI and MDI. TDI rubbers are the industry go-to, but MDI rubbers can also be useful for certain projects. Urethane comes in many forms (plastic, coatings, rubbers, foams) and has high adhesion to most surfaces, which is why it will require a release agent in all molding applications. VFI has developed a line of urethane rubbers with best-in-class release properties that can be used in place of silicone. You will still need release, but it will release much cleaner, providing better parts and extended mold life.
• Silicone – There are two types of silicones for mold making: platinum-based and tin-based. Platinum-based is preferred due to its dimensional stability, durability, and release properties. The reason you should not use tin-based rubbers is that they will shrink over time and lose tear strength. Since concrete castings need to be consistent in shape and size, this material won’t work well in the long term. The main use of tin-based silicone molds is making thin texture mats where you do not need dimensional stability.

What Is Decorative Concrete?

Non-structural concrete elements that have intricate designs and patterns are considered decorative.

Rubber molds are used to create castings such as pavers, ornaments, statues, fireplace accents, modular outdoor kitchens, and other architectural features. While metal, wood, and plastic molds can come in handy for some precast projects, they are generally not great for decorative concrete.

Factors to Consider When Choosing a Liquid Rubber

What Properties Do You Require?

1. Hardness

Shore hardness is a determining factor in whether a concrete caster will use silicone or urethane rubber. Most rubbers are measured on the Shore A scale for hardness. Urethane rubbers range from 20-90 A on the Shore A scale, while most silicone rubbers are between 10-60 A. A general rule of thumb is the softer the rubber, the easier it will release from complex shapes. However, a softer rubber will not be as durable. Hardness will also contribute to the level of detail you can get.

The following rubbers are recommended for projects that require the following hardnesses:

• 10-30 A – Silicone rubber is usually the best option if a softer, flexible mold is crucial. Its flexibility generates easy release from intricate details and undercuts without tearing the mold or breaking the casting. You can also use it on delicate architectural restoration projects without damaging the original piece. There are brushable and pourable options.
• 30-60 A – TDI urethane rubber is recommended for these projects because it works better than silicone at these hardnesses and is more cost-effective. TDI is recommended over MDI rubbers because it is less sensitive to moisture, making it easier to use in various environments. These hardnesses are a good middle ground for cast stone, manufactured stone, and advanced detail formliner projects.
• 70-90 A – A combination of TDI and MDI rubbers can be used when an extremely rigid, durable mold is required. MDI can be great for simple formliners with rigid backing because of its increased adhesion and tear resistance. These materials also work well for concrete stamps and rollers.

Note: If you’re using any material above 90 A, it will always be an MDI urethane. This is also where urethane will get rigid and feel more like plastic. Urethane at harder durometers can be great for making master models to protect fragile originals.

2. Tear strength

Most silicone rubbers are lower in hardness, so tear strength is crucial for durability. They generally will have higher tear strength than urethane at the same durometers. This allows them to remain intact when demolding from intricate details.

Urethane rubbers tend to have better tear strength at higher hardnesses, making them extremely durable for large projects. If you’re making massive forms, they are better at holding up to the weight of the concrete.

3. Tensile strength

This property is also similar for both urethane and silicone. Silicone will have better tensile strength at lower durometers, while urethane will have better at higher durometers. This is another property that’s important when you’re working on more detailed, fragile work. On the other hand, it is also useful when making large molds that need to hold up in abrasive situations.

4. Elongation

The opposite effect happens with elongation. At lower durometers, silicone rubbers will have poor elongation, while urethane’s elongation will be better. Elongation is lower at higher durometers because the molds have lower flexibility without the ability to stretch. Demolding urethanes with higher elongation is easier because they will also have increased flexibility.

Conclusion: silicone has better properties at lower durometers, while urethane has better properties at higher durometers. Which you choose will still be very dependent on your unique project.

How Long Do You Need the Mold to Last?

The durability of the mold, how frequently you use it, and how well you maintain it will all factor into how long it will last. A reusable mold is desirable, but it is not always necessary. Silicone molds are great for low-volume and unique concrete work, but their poor abrasion resistance makes them less suitable for high-volume concrete projects.

If you need a highly reusable mold for high-volume production, urethane should be your go-to. It is the best choice for most concrete casting projects because it offers superior abrasion resistance. This allows you to get up to 100 casts from a single mold.

What Is the Budget of Your Project?

At surface level, silicone tends to be more costly than urethane rubber. You must account for how much material you need and how much waste you might generate in making the mold. Waste will also coincide with the reusability of the mold. It may not be worth it to spend more on silicone if you need to cast a larger quantity of concrete.

A way to save money is by using rigid or semi-rigid foam to back your urethane mold. This will also make your mold more lightweight. Lightweight molds for concrete casting projects can be beneficial if you move them around often because thick rubber can get heavy.

What Are Your Project Deadlines?

How long it takes to make the mold can have an influence on the molding material you choose.

Certain materials can be brushed on a model or poured into a mold box or form. Pouring the material is easier and saves you time, labor, and materials. Brush-on molds must be layered on and require a supportive mold shell, which can take longer to make. You will need to have the skills to make a skin mold as well.

For processing times, most urethane molding rubbers have a standard demold time of 16 hours. Some MDI formulas are as short as 4 hours for faster turnaround on part production. Silicone rubbers tend to have demold times between 16-24 hours.

Alternatives for Decorative Concrete

Urethane Form Coating – Another way polyurethane can be used is by spraying it onto an EPS form before casting concrete into it. The coating creates a releasable surface that works well for decorative formwork.

The form hard coat isn’t as permanent as rubber, but it’s a great option for 1-5 uses. This spray-applied method also allows for a faster turnaround on custom pieces, especially since post-work is not required.

Urethane Hard Coat – Alternatively, VFI offers high-pressure and Qwik Spray hardcoats for architectural shapes and forms. You can shape the foam and encapsulate it with a durable urethane hard coat before painting it to look like natural materials.

Epoxy Form Coat – Additionally, if you need to roll a form coat onto metal, wood, or EPS forms, we recommend using our VFI-4385 82 D Form Coating Epoxy.

Contact VFI if you have questions about whether urethane or silicone rubber is a better option.

Why Is My Concrete Casting Shiny?

Decorative concrete elements are used to enhance the architecture of residential and commercial structures with various colors, textures, and patterns. Their most desirable trait is the ability to mimic other natural building materials at a lower cost.

However, issues can occur in the manufacturing process that will affect the casting’s final finish. These issues can make the casting appear shiny rather than matte, like natural stone, brick, and wood. The shiny appearance will typically occur from using too much mold release or bad pigments.

Reasons Your Concrete Finish is Shiny/Glossy

1. Overapplying Mold Release or Sealer

A shiny casting typically occurs from mistakes made in the initial process of making the concrete mold. One of the most popular materials for making these molds is liquid urethane rubber. When trying to make a mold through additive or subtractive manufacturing, it will always appear to be man-made or artificial. Urethane rubber will avoid the artificial look by copying the natural profile of a stone and provide a matte finish.

Before using the rubber, you have to prepare the molding surface. It’s how you prepare the surface that can change the final finish of your mold and future castings.

Situation 1: The Master

In the process of preparing your mold box or form, you have to apply a release agent. You might also have to apply a sealing agent directly on porous masters. Both these materials will help prevent the rubber and molding surface/master from sticking together. However, the amount of release and sealer you use can affect the finish of the mold. If used in excess, these materials will cause shininess on the mold.

For sealing agents, VFI typically recommends using a combination of 80% mineral spirits to 20% petroleum jelly by weight on porous surfaces. If your mixture is too heavy on the petroleum jelly and you’re overapplying it, it can increase the shininess of your master.

On mold boxes and masters with intricate details and low points, overapplication can lead to pools or puddles of mold release and sealer. This will create a residue on your molding surface that will be picked up by the rubber as it cures, resulting in a glossy finish. Not allowing the release or sealer to dry before pouring the rubber can also result in a poor surface finish.

After demolding, you’ll notice a shine in certain spots on the interior surface of the mold. This occurs because the urethane rubber is able to capture extreme detail and texture. This ability is why it’s such a desirable material for concrete molds, but it can also make it tricky to get the finish you desire. If you were to cast concrete into that mold, every casting that comes out of the mold will have distinct areas with a glossy appearance.

Situation 2: The Mold

Maybe your urethane rubber mold wasn’t shiny after you demolded it, but there’s still a chance you could make shiny castings. The mold will still need to be released to prevent the concrete casting from sticking to it. If you use too much release on the mold or don’t allow it to dry, it can also create a shiny finish when you cast the concrete. Sometimes, it can even cause pinholes and other defects in the concrete. If you don’t use release during this step, the mold will bond to the wet concrete.

2. Bad Pigments Were Used

Decorative concrete manufacturers typically color concrete with powder, liquid, or granular pigments. Pigments transform the concrete from a standard gray color into whatever color you need to replicate natural building materials. Pigments will either be added directly to the concrete mix or applied to the surface of the mold. Using pigments that are incompatible with or have surpassed their shelf life can cause the concrete to appear shiny.

Solutions

Applying a release agent is a delicate balance in both the molding and casting process. Avoid using too much sealer or release in either step. If pools of these materials are not wiped away and allowed to dry before casting, they can cause permanent shine and glossiness, discoloration, and even bubbles. If you remove the excess ahead of time, it shouldn’t impact the finish.

Always check the manufacturer’s instructions when using new materials. A good rule of thumb when using release agents is to apply 2-3 coats of the material in thin films. Wait for the release to dry before applying another coat. The same can be said when using a sealing agent. This will help eliminate pools of material.

Be aware that you will have to apply release to the mold after each casting as the release will wear away. This should help you determine how much release is needed for effective demolding and to produce castings without a shiny surface. Before applying more release, you’ll also want to clean the mold to get rid of previous release or concrete residue.

Because most decorative concrete projects use pigments to color the concrete, check the expiration date before use. Otherwise, it could result in a poor surface finish.

Contact VFI if you’re still experiencing issues with your castings appearing shiny, and we will do our best to provide potential solutions.

TDI vs MDI Urethane Rubber for Concrete Casting: Which to Use?

Urethane rubbers are versatile 2-part materials used in the concrete manufacturing industry to produce small and large precast pieces. The material you choose for your project will depend on your application, processing requirements, and manufacturing environment.

Because the chemical composition of polyurethane rubbers can be different, their properties are controlled by the types of prepolymers used to make them. As one of the core components of urethane, the type of isocyanate (A side material) is one material that changes the way it performs. The most common isocyanates used for urethane rubbers are TDI and MDI.

What Is TDI Rubber?

TDI rubber is a type of urethane that uses a prepolymer called toluene diisocyanate. TDI-based rubbers are standard in the industry and usually come with premium properties compared to MDIs.

The prepolymer is actually less hazardous than an MDI prepolymer and has a lower risk of causing respiratory irritation, skin sensitization, and other health issues if in direct contact. However, you should always utilize proper personal protective equipment (PPE) when using urethane rubbers. Regardless of potential hazards, they are an effective material for making durable concrete molds.

Benefits of using TDI:

• Lower exothermic reaction. The amount of heat generated while the rubber cures is lower than MDI. When less heat is used to cure the rubber, it will have better dimensional stability (lower shrinkage). The size of the form you are pouring will be consistent, and the rubber will retain its original shape.
• Lower sensitivity to moisture. Urethanes are sensitive to moisture and will bubble if exposed to a high amount in the environment or during application. What’s beneficial about TDI rubbers is that they can handle moisture better than MDI rubbers. This means you don’t have to work in as stringent conditions for the rubber to cure without bubbles.
• Extended pot life. If you’re pouring large and intricate forms, you will need ample time to work with the material. Most VFI TDI rubbers come with a 20-30-minute pot life, with some exceptions. This makes processing easier and reduces the risk of mistakes during mixing and pouring.
• More variability. TDI rubbers offer a wider range of properties and Shore A hardnesses, going from 25 A to 90 A. Due to the increase in options, there are also more application possibilities. Softer rubbers can be used to make more intricate molds, while harder rubbers can be used for less detailed but durable forms. The softness of lower durometers provides more give for easy demolding on complex parts. VFI also has a line of lower durometer TDI rubbers with improved release abilities. This means that concrete pieces will have lower breakage rates when demolded.

Where to Use?

• Manufactured stone: One of the most common applications for TDI rubbers is manufactured stone molds. At lower durometers (30-60 A), TDI rubbers capture intricate details without degrading after first use due to high abrasion resistance. A few materials VFI recommends include VFI-2143 45 A TDI Molding Rubber and VFI-2163 60 A TDI Molding Rubber. Our line of Max Release molding rubbers are also beneficial for this application because they demold from intricate details easier using less release.
• Cast stone: Like manufactured stone, cast stone applications benefit from using lower durometer TDI rubbers. They come in durometers as low as 25 A, which is good for making detailed features, such as wall trim, columns, ornaments, and more. Standard materials for this application include VFI-2123 25 A TDI Molding Rubber or VFI-2143 45 A TDI Molding Rubber.
• Formliners: Whether you need advanced detail or simple formliners, the range of TDI rubbers available can accommodate any project. 70-90 A rubbers withstand the weight of concrete for these projects due to their higher tensile and tear strengths. 50-70 A rubbers are recommended if more detail is needed. However, most concrete producers will use MDI rubbers instead if they are creating simple formliners due to cost.
• Stamps: Because stamps are made thin to comply with weight restrictions, a harder durometer material is used. Rubber between 70-90 A will offer the rigidity and durability needed, so the stamps can be stood on and moved. VFI’s recommended materials include VFI-2180 80 A TDI Molding Rubber and VFI-2190 90 A TDI Molding Rubber.

What Is MDI Rubber?

MDI rubber is a type of urethane that uses a prepolymer called methylene diphenyl diisocyanate. When using MDI rubbers, you need to work in a controlled, high-production environment because the material is highly sensitive to moisture.

Benefits of using MDI:

• Cost-effective. MDI rubbers are preferred due to their lower cost and ease of use. It is because you have to work in a high-production facility that manufacturers turn to TDI instead. There are also fewer options to choose from when it comes to MDIs because they work best at higher hardnesses.
• Better adhesion. When it comes to molding and casting, the last thing you want to see is your rubber sticking to other materials. However, there are some applications where some adhesion is desired. Some formliner or stamp manufacturers desire the ability to adhere their rubber to a rigid backing material like wood. This allows them to insert attachment points which helps with the movement of the formliner and prevents the liner from shrinking or expanding in extreme temperatures. Once bonded with the desired substrate, MDI becomes strong and is difficult to tear.
• Better processing. While the moisture sensitivity of MDI rubbers makes them less desirable, they do offer other benefits in terms of processing. MDI processes better at lower viscosities, so you don’t have to worry about working at room temperature (77°F) when making your molds. You also can choose between fast and slow options for quicker demold and turnaround on production. You just have to be wary of the pot life on faster materials.

Where to Use?

• Formliners: Since most MDI rubbers are harder in durometer, they are preferable for large projects like reusable concrete formliners. Their strength makes them able to maintain their shape under the weight and pressure of concrete. Since they have strong adhesion to other materials without tearing, they work well if they need to be adhered to backing panels for ease of movement with cranes. VFI’s recommended materials include VFI-3171 70 A MDI Molding Rubber and VFI-3181 80 A MDI Molding Rubber.
• Stamps: The rigidity of high-hardness MDI rubbers is also desirable for stamping projects. Harder rubbers have better strength, especially when poured thinner, and are better at printing higher detail. Their strength also allows them to maintain their shape when people are stepping on them during the stamping process. VFI’s recommended materials include VFI-3170 70 A MDI Fast Molding Rubber and VFI-3180 80 A MDI Fast Molding Rubber. These are faster MDIs since stamps are smaller and don’t tend to require longer pot lives like formliners.
• Rollers: The rigidity and durability of MDI rubbers are also desirable for creating concrete rollers. They withstand the abrasive qualities of concrete while also being sturdy enough to leave a desired pattern. They offer a quicker way to imprint concrete compared to rigid or flexible stamps. VFI would recommend the same materials as mentioned above.

Contact VFI if you’re still unsure whether you should use an MDI or TDI molding rubber.

Liquid Rubber for Decorative Concrete Stamps

When it comes to making decorative concrete stamps, liquid rubber is typically the most desired material for the job. Concrete stamps require a level of strength, flexibility and detail that polyurethane can provide. It is the best material for replicating the look of natural materials at a lower cost compared to wood, metal, and plastic stamps.

Because urethane rubbers come in a range of Shore hardnesses, they are utilized in a handful of concrete applications. The rubbers chosen for concrete stamps are typically more rigid, but they also maintain some flexibility and provide great abrasion resistance in comparison to other rubbers like silicone or latex. Urethane’s abrasion resistance makes it long-lasting and reusable, so contractors can use the same stamp in multiple projects.

What Are the Different Types of Concrete Stamps?

Because urethane rubber is extremely versatile, various types of concrete stamps exist. The main types made with these materials are rigid or semi-rigid mats and flexible texture skins. A combination of these tools is recommended for most projects. They can be used in various indoor and outdoor environments, including courtyards, gardens, pool decks, driveways, sidewalks, entryways, patios, and more.

Rigid and Semi-Rigid Mats

These are the strongest and most durable of all concrete stamping tools. Since they are used for the bulk of the stamping project, they are a bit on the larger side to cover more ground. For contractors to be able to lift them, they will typically have handles molded in to help move them and continue the pattern in the concrete.

Most concrete mats need high strength and structure, so a higher durometer rubber is recommended. When they have higher rigidity, they are better able to leave a detailed impression on the concrete. They produce realistic brick, stone, slate, tile, and wood textures. Each stamp has a unique pattern variation to provide a more authentic look. They will typically have grout lines that can be further indented with special tools.

The rubbers VFI generally recommends for the job are VFI-2180 80 A TDI Molding Rubber and VFI-3180 80 A MDI Fast Molding Rubber. These are firm materials that are good for making these mats. At 80 A, they offer the necessary durability to allow contractors to stand on them during the stamping process.

MDI-based materials work best in controlled, high-production environments where little moisture is involved. The cost and processing abilities of these rubbers are typically most desirable for making stamps. They process better at colder temperatures and cure faster than some TDI rubbers. On the other hand, TDI rubbers offer lower moisture sensitivity, lower exothermic reaction, and extended pot life.

Flexible Texture Skins

Compared to stamping mats, texture skins are much thinner. Their thinner quality makes them lighter and easier to move around on the worksite. They are usually made with feathered edges so they can be rotated or overlapped. They will not have simulated grout lines or joints like rigid mats. This means they don’t need to be aligned in a specific pattern, creating a seamless appearance on the concrete.

The rubber material used for these skins usually feels softer because they are poured thinner for more flexibility on curves, sloped areas, hard-to-reach spots, and vertical surfaces. For increased flexibility, VFI-2190 90 A TDI Molding Rubber is a good choice and also provides great detail.

Specialty Tools

Other tools urethane rubber can be used to make for concrete stamping projects include:

• Medallions are not the most used stamp, but they can elevate a concrete project. They add a more sophisticated, unique touch. A lot of the time, these stamps are custom-made to fit an aesthetic desired by the customer. They will then blend with other rigid mats or texture skin patterns. Examples include compass roses, sunburst designs, Celtic knots, and more. Because urethane rubber is so pliable, it can replicate any original design.
• Texture rollers are also stamping tools that make it easier to imprint a consistent pattern on concrete. Since the pattern is attached to a long handle, contractors can cover more ground quickly. A tamper is not used to press the pattern into the concrete, so the detail won’t be as prominent with this method. This tool is better in applications where detail isn’t as critical, like corners and borders. VFI-3180 and VFI-2190 can be used to make these tools since a harder rubber will help the pattern imprint better detail.
• Edge liners can be used around the borders and vertical surfaces of countertops, fire pits, stairs, benches, etc., to easily imprint textures, patterns, and profiles for an extra touch on stamping projects.
• Stamped concrete can also be used with other decorative concrete elements, such as cast stone and manufactured stone. Urethane rubber molds are used, but they will be lower in durometer than urethane stamps. Check out VFI’s TDI specification sheet for more information.

How Are Concrete Rubber Stamps Made?

Stamped concrete looks realistic because a natural material, like flagstone, ashlar slate, or ceramic tile, is used as a model when making the stamp. 2-part urethane rubber conforms to the details and shape of the original pattern, so there are limitless options for the types of patterns and textures you can replicate. If a large stamp needs to be made, multiple pieces are assembled, and clay is placed between gaps to act as grout lines.

Since the model materials are naturally porous, they must be sealed before the rubber is poured. VFI recommends an 80% to 20% combination of mineral spirits and petroleum jelly by volume. After a few layers of the sealer are applied, a mold release should be used on the models and any surface the rubber will come into contact with.

Some urethane rubber users will pigment the rubber for color coding purposes. Color coding can help contractors differentiate between patterns during the stamping process to prevent unwanted repetition. A urethane pigment is added before the rubber components are combined.

All urethane rubbers come with exact mix ratios by weight and volume so they can properly cure. Once the rubber is measured and mixed thoroughly, it is poured into the form to create the stamp. Depending on the size of the stamp and the needed strength, most rubbers can be poured to 3/8 of an inch thick. If a softer rubber is used, it should be poured thicker (about ½ of an inch thick).

VFI’s MDI rubbers offer shorter pot lives and demold times than some TDI rubbers. This is a great feature if you’re making multiple concrete stamps for one project. Since concrete stamps typically aren’t too large due to weight restrictions, you should have plenty of time to mix up and pour the rubber before it starts to cure. The cure time for VFI’s materials is 4 hours, so the stamp can be demolded on the same day for increased production.

How Long to Let Concrete Set Before Stamping?

The concrete should be firm enough to allow contractors to walk on it before they begin stamping. However, it also needs to be a bit soft to allow the stamp to leave a detailed impression. The more rigid the stamp, the sooner you can start stamping. It’s important to work quickly; otherwise, you might end up with a lighter texture as the concrete hardens.

How long do rubber stamps last?

If the urethane stamp is properly cared for, it can last for multiple jobs. The best part is that they are incredibly easy to maintain. After a stamping project, they can be cleaned with soapy water and a brush or a pressure washer.

Concrete stamp mats should be stored flat. If they need to be stacked, they should be stacked square on top of each other to prevent warping or bending over time. If possible, it’s better if a set of stamps has its own pile. Do not bend or roll them. Store them in a temperature-controlled environment away from direct sunlight. If you store them outdoors, the sun may cause them to deteriorate or chalk.

Contact VFI if you have additional questions about concrete stamping materials or are interested in other molding rubber options.

Why Is My Urethane Foam Not Expanding / Collapsing?

If you’re familiar with rigid or semi-flexible urethane foam, you know that each product has its own approximate expansion rate. The lower the foam density, the more it will expand. You’re trusting that it will expand to a specified amount multiplied by its volume, as stated on the technical data sheet (TDS). So, when it doesn’t do what’s expected, you’re probably wondering what went wrong.

In some cases, it might seem like the foam reaches the desired expansion rate, but then it will deflate before it cures. Urethane foam might not expand or will rise and then deflate for several reasons, with the most common being contamination or application issues.

Reasons Urethane Foam Doesn’t Expand

1. Contamination

Some materials are not compatible with urethane foam and will cause expansion problems. Silicone creates the most common issues because it is a low surface tension contaminant. If you have excessive amounts of silicone on your molding surface, your foam may rise but then it will collapse. When this occurs, it will kind of look like a deflated lung. This typically happens when using silicone-based release agents or new tin-cured silicone molds that haven’t fully cured.

2. Mixing Issues

As two-component materials, if you don’t mix the correct amount of the A (Iso) and B (Poly) sides, problems may occur. All urethane foams have a different mix ratio by weight, while most are 1A:1B or 1A:2B by volume. If you use too much of one component, it’s not going to react the way you’re expecting it to. It may never expand, or it will not develop a uniform cell structure.

Problems can also occur if you are not thoroughly mixing the two components. Expanding foams can be tricky to work with because of their extremely short pot lives and fast rise times. Mistakes with mixing occur because people rush to pour the material before it starts to expand.

3. Cold Temperatures

Since urethane foam is a water-based material, you need to consider the temperature of the environment, the material, and the molding surface. If you are working in cold temperatures or if your molding surface is too cold, the foam might experience less expansion or collapse as it cures due to separation of the A and B sides from the low temperatures. Temperatures below 60°F can cause these problems and there is also a risk that the material may freeze.

4. Curing Issues

If you move the foam or touch it while it is still expanding, this interference could cause cells to collapse. The area you touched will deflate and create a mass that will be hard to remove from the foam.

Also, if you allow it to expand but remove it from the mold too soon, you are not giving it enough time to gain strength. Even if it appears cured and firm on the surface, it probably hasn’t cured internally. Eventually, it will deform or deflate without a structure to hold its shape.

Solutions

Always follow the manufacturer’s instructions before working with urethane expanding foams for the best results. Temperature is one of the most important things to consider when using any urethane material. Working at higher temperatures can help to increase expansion. It’s recommended to bring the material temperature to a minimum of 65°F, work at room temperature (77°F), and use a heated mold.

You can heat the mold up to 120°F, but doing so will decrease the already short pot life. If your material is too cold, bring it up to room temperature before dispensing.

If you need to prevent adhesion from occurring, avoid using silicone-based release agents. The most recommended release agent for foam is a wax-based, silicone-free release agent. These release agents have proven effective in releasing urethane foam from various surfaces.

If you use a tin-cured silicone mold, you must ensure it is fully cured. You can do this by waiting for the allotted cure time or post-curing it in an oven. Often, it is best to avoid using a silicone mold and just use a metal mold when possible.

Thoroughly premix the B side before combining it with the A side. Ensure you are using the correct mix ratio as stated on the manufacturer’s technical data sheet. Once combined, mix quickly and thoroughly with a drill or power mixer. Drill mixing introduces more air into the system and will cause the foam to expand more. Mixing by hand will not provide you with an adequate mix before the pot life expires. The faster and harder you are able to mix, the better it will expand. For uniformity, make sure to scrape the sides and bottom of the mixing container as well.

Avoid moving or disturbing the foam while it cures. Allow it to remain in the mold or form until it has fully cured to prevent deformation. This will typically be 2 hours when left at room temperature. Cure times depend on the material, so always check the TDS. Thinner pours will require a longer cure time.

Contact VFI if you have other issues with urethane expanding foam. We’ll be happy to help you find solutions or alternatives to your problems.

High-Quality Foam Coatings for Small Theming Projects

Foam coats for theming projects like sculptures, props, and architectural shapes are desirable for small fabricators, scene shops, and DIYers alike. In order to protect your foam project in the long term, it needs to be coated, especially if placed outdoors.

There are a range of coatings available, but not all materials will stand the test of time. If you’re going through the effort to make an intricate piece, you’re going to want to make sure it lasts.

What Is a Foam Coating and What Is It Made Of?

A foam coating is a material used to create a durable shell over various foam materials, including EPS, XPS, Styrofoam, or polyurethane. Without a coating, these foam projects are exposed to daily wear, weather, impacts, and other conditions that degrade them.

Some basic coating options are made of a mix of plastic paint, plaster, mortar, or sand, but these materials have a habit of chipping, cracking, or breaking over time. Other materials are dry powder that you mix with water, and it hardens, but they won’t provide a finish as smooth as some other options.

We’ve also seen some people use Drywall mud, but that is another material we wouldn’t recommend. Over time, the material will crack due to temperature changes. It also weighs a lot more than a standard foam coat.

VFI offers several high-end foam coatings for small projects. There are two distinct options we would recommend: brushable hard coats or cartridge-based hard coats.

• VFI-2519 75 D Brushable Hard Coat
• VFI-2626 65 D Brushable Hard Coat
• VFI-6171 70 D Qwik Spray Hard Coat
• VFI-2538 QS 70 D EPS Form Hard Coat

These coatings are polyurethanes. Depending on your requirements, there are both ASTM E84 Class A fire-tested options and options where regulations are not a concern for outdoor themed elements.

The coatings will enhance the performance characteristics of the foam as well as its aesthetics. They also allow you to handle the piece without worrying that it will break from accidents or planned impacts.

Smaller fabricators normally choose to use a brushable hard coat. These coatings are convenient with a simple 3A:1B by volume mix ratio, and they give you greater control over smaller pieces during application. You can easily coat small corners, intricate designs, and curves without diminishing details. Plus, you only use what you need, whereas spraying can lead to wasted material from overspray.

On the other hand, if you’re a small fabricator or scene shop that is consistently working on new projects, the Qwik Spray formula can be more beneficial. The cartridge-based system is great for low-volume applications for projects up to 4 x 4 or 4 x 6 feet in size. Compared to high-pressure spray equipment, the VFI-7500 Qwik Spray Gun is more portable if you need to create theming projects on the go.

What Is the Process of Foam Coating?

Once your foam piece is carved and shaped, you can apply a urethane hard coat directly to the raw foam. Depending on the product you choose, the material will have specific application requirements.

A brushable coating, for example, will require mixing and measuring before application. This part of the application process is where mistakes tend to be made. It’s essential to combine the correct amounts of the two components (A and B sides) for the coating to work and dry properly.

You also have to be wary of the environment you’re working in. Urethane is a moisture-sensitive material. If you do not work in a well-ventilated, temperature-controlled workshop, you may experience bubbling.

For more information and tips on using brushable coatings, check out VFI’s blog.

Alternatively, VFI’s cartridge-based formula doesn’t require mixing. You just uncap the cartridge, put on a static mix tip, assemble it in the gun, and it’s ready for spraying. It’s faster to apply and post-work as it sets in seconds.

The Qwik Spray applicator can provide a smoother, consistent finish that gives the foam piece a more polished look. This finish is especially beneficial for theming applications where aesthetics are crucial to the overall design.

For a step-by-step tutorial on the applicator and cartridge assembly, check out VFI’s How to Use the Qwik Spray System blog.

The hard coat itself is only one step in the theming process. After the hard coat has cured, it should be sanded for a smooth, aesthetically pleasing finish before paint is applied.

An acrylic or industrial-type automotive paint can be used to make them appear more realistic. The hard coats alone are not UV stable, so a top coat is required to prevent them from yellowing and degrading.

How Long Does a Foam Coat Take to Dry?

The time after application that a hard coat needs to dry will depend on the formula and application environment.

VFI brushable coatings are usually ready for sanding and painting the next day, while the Qwik Spray formula dries much faster, and post-work can begin a few hours after application. Ultimately, the coating needs to cure to a desirable hardness first.

Temperature is a big factor in the curing of these coatings. Cooler temperatures below 72°F can delay cure. That is why it’s recommended to work at or above room temperature whenever possible. Just be aware of the relative humidity because a large amount of moisture can affect the finish.

What Is a Foam Coating Used For?

We’ve seen theaters and scene shops across the county use brushable and Qwik Spray foam coatings to protect various projects. From handheld props and small scene elements to outdoor holiday, garden, and lawn décor, theming hard coats are only limited to your imagination.

These coatings are also useful for creating small displays for retail stores, amusement parks, and museum exhibits. A high-pressure sprayable coating should be used if you are working on larger projects.

If the piece will be subject to physical abuse or needs to last a long time, urethane hard coats are your best bet. They improve the abrasion, weather, chemical, and fire resistance of the foam as they encapsulate it entirely.

Most foam coatings are generally not very flexible or pliable. If you’re using softer foam, we also have alternative coatings that can be applied to those surfaces to prevent cracking. VFI-270 70 A Polyurea Spray Coating is a polyurea coating on the Shore A scale, meaning it can maintain the flexibility of flexible surfaces. This material will require high-pressure equipment.

Contact VFI for more information on all our foam coatings for your next project.

Protect Work Trucks with Abrasion & Slip Resistant Coatings

Construction, emergency, and utility vehicles are all integral parts of day-to-day life in various industries. Heavy-duty equipment is expected to function indoors and outdoors. It must face weather and road hazards year-round, including extreme temperatures, dirt, rocks, and other road debris. It should also be able to handle the frequent movement of heavy loads.

Without protection, these conditions can erode and wear surfaces, causing scuffs, scratches, and dents. These defects can then generate rust and corrosion that reduces the longevity of your equipment.

An abrasion and slip resistant coating is desirable for protecting open and enclosed work trucks from the damages mentioned. With a textured grip, they can also reduce the sliding of cargo to prevent interior damage. This can help limit slip accidents and injury during cargo loading and unloading as well.

Factors to Consider When Choosing a Protective Coating

Before choosing a protective coating, there are several factors you should consider. Assessing the following will help narrow the best one for your project.

• Hardness. Coatings with higher durometers tend to have good abrasion resistance and prolong the lifespan of the surface. However, the harder the coating, the more brittle it will be. If a coating is too hard, impacts can cause cracks and delamination from the surface. Finding a coating within the 40-60 D range will offer durability with some flex for withstanding abrasion and impacts.
• Flexibility. While these coatings must be hard, they also need some elasticity to prevent wear from weathering. A good balance of hardness and flexibility will keep the coating intact during temperature extremes. This prevents cracking or failure. It also keeps the watertight seal intact so water, dirt, and other debris can’t cause rust and corrosion on the underlying surface.
• Properties. Tensile strength, tear strength, and elongation are important for the coating’s longevity. These properties are part of what makes the material durable, so it holds up against heavy wear without deforming, tearing, or cracking. Other properties allow the coating to support heavy loads, prevent high friction, and maintain adhesion to the surface.
• Surface Finish. Depending on where you spray the coating, you might want a textured finish for increased grip. If you’re applying the coating to work truck floors, you don’t want a smooth surface as this could cause people or cargo to slip, causing accidents or damage. Some coatings come with an inherent texture or allow you to customize the texture to your liking.
• Thickness. When a coating is applied thicker, it takes more abrasion and impact to wear away and expose the substrate to the environment. An abrasion resistant coating is often applied at 80 mils for extensive protection.

What Is the Best Protective Coating for Work Trucks?

Some of the best coatings that combat abrasive wear are made of high-performance thermoset polymers. They are commonly used when work trucks require a high degree of protection as they provide the needed amount of hardness and flexibility. The coatings VFI recommends are polyurea and polyurea hybrids.

Coatings like these that are hard yet flexible and applied thick tend to be the best at preventing wear. They work well over metal surfaces, such as steel and aluminum, making them perfect for reducing damage that can deteriorate your fleet. By applying these coatings, you are extending the life of your coated parts. They maintain their structure and appearance even after prolonged wear.

Another desirable quality of these coatings is chemical resistance. Since many work trucks are used in the oil and gas, agriculture, and automotive industries, it’s important for the coating to resist damage from oils, fuels, solvents, and more.

Spray coatings are also highly customizable. Polyurea and hybrids can be tinted if you want a custom color to match the vehicle or company branding. Not only do you get the function of using a protective coating, but you get the aesthetic benefits as well. However, VFI coatings and most coatings on the market are aromatic. This means they will fade if exposed to UV rays for long periods. Applying an aliphatic topcoat is essential to prevent this from happening.

Polyurea coatings are the premium option when it comes to protecting your work truck. They tend to offer higher tensile strength, tear strength, and elongation due to the raw materials used to make them. They are also more moisture-insensitive, allowing you to use them in environments with high levels of moisture or humidity.

However, if you don’t require premium properties or characteristics of a polyurea, a hybrid coating is a great option. It offers a good balance of cost, properties, and performance. Hybrids have some polyurethane content, making them more sensitive to moisture. If you can avoid applying them in moist or humid environments, this shouldn’t be a problem.

What Are Common Applications for These Coatings?

From pickup and dump trucks to tractors, trailers, and service bodies, it’s essential to keep your vehicles in good condition so they don’t break down when you need them. When they do break down, money is lost from excessive downtime for repairs. There’s no limit to what parts of work vehicles you can protect, with the most common being:

• Floors and ramps. By applying a coating with a textured finish on surfaces you walk on, you’ll have better traction for secure footing when loading and unloading. Anti-slip protection is especially helpful for open work trucks that might get wet from outdoor conditions. It can also help prevent cargo from shifting in transit, protecting the cargo itself and your work vehicle from dents and dings.
• Outer vehicle parts. When you apply a coating to critical areas of your vehicle like rocker and bumper panels, fenders, and wheel wells, you’re protecting them from road and weather hazards. So, rather than finding dents, nicks, and rusted-out spots on your vehicle, you have ensured seamless protection.
• Toolboxes. Spraying the inside of work truck toolboxes and compartments can also prevent damage from the movement of tools and equipment you store on the drive. This will keep the underlying surface protected from scratches, impact, and more that could result in rust and corrosion.

Contact VFI for more information on the best coating solutions for your work trucks.

What Is Causing Bubbles or Blisters in My Polyurea/Hybrid Coating?

Once you’ve applied a fresh layer of polyurea or hybrid coating to a surface, the last thing you want to see are bubbles or blisters. Whether they appear in one spot or are seen throughout the entire coating, they are typically caused by the same thing: trapped air. Bubbling occurs when pockets form beneath the coating, which causes the coating to lift and create that bubbled appearance. Bubbles not only ruin the coating’s appearance but also result in adhesion failure.

Reasons Polyurea/Hybrid Coatings Bubble

Reason #1: Poor Surface Preparation

Option 1: Proper surface preparation is key to avoiding bubbling. When bubbles form, it is typically because contamination on the surface creates a barrier and prevents the coating from adhering. Rather than sticking to the surface, the coating will adhere to dust, debris, oils, etc., that are present. Once the coating has cured, over time it will blister and delaminate from the surface.

Option 2: Apart from an unclean surface, bubbles can also occur if the surface isn’t prepared in other ways. Some surfaces, to generate adhesion, will need to be abraded. This is typically done by sanding, shot blasting, or abrasive blasting to a certain degree. If the proper surface profile is not created, you will notice bubbling issues over time.

Option 3: Some surfaces will create more bubbling problems for coatings than others. If you are working over a porous surface, you need to make sure moisture is not trapped before applying the coating. When a coating is applied without proper surface prep, moisture will become sealed underneath. If the surface is subject to high temperatures that increase pressure, the only place for that moisture to go is up toward the coated surface, causing a blister.

Reason #2: Incorrect Mix Ratio

While mixing issues aren’t typically a problem for high-pressure spray coatings, sometimes the spray equipment can become off-ratio. If sprayed at the wrong mix ratio, it might be gummy and cause adhesion issues. This gumminess can indicate that too much of one component was used. While polyurea isn’t as sensitive to moisture as hybrids, it can be affected by being off ratio and will cause bubbles. An off-ratio issue will usually only occur due to incorrect equipment setup or required maintenance.

Another potential off-ratio issue can occur when using cartridge-based spray equipment. It’s important to start spraying off the surface you want to coat first. It takes a few seconds for the coating to mix thoroughly in the static mix tip. If you immediately start spraying the cartridge on your designated surface, you might notice bubbles in the coating once it has cured. If you are using the VFI Qwik Spray System, check out our how-to-use blog here for more tips.

Reason #3: Temperature Issues

If you’re working in extreme temperatures, whether it’s hot or cold, they can affect the way your coating cures, causing bubbling or pinholes. Applying a coating in direct sunlight or high heat will cause the coating to cure rapidly, which will accelerate the cure and may cause adhesion issues, which will make a blister. On the alternative, if you’re applying in colder temperatures, it slows the coating’s ability to cure, which can also leave room for more bubbles to form with uncured or partially cured material.

Reason #4: Moisture Issues

Polyurea coatings typically will not have moisture issues due to their insensitivity. However, while the moisture wouldn’t necessarily react with a polyurea, the coating wouldn’t be able to properly adhere to a wet surface. This lack of adhesion would generate blisters.

There are a few ways moisture can cause bubbling in hybrid coatings. If there is moisture on or in the surface, in the atmosphere, or within spray lines, bubbles can occur.

• Surface moisture. If you do not properly dry the surface before applying the coating, the coating will react and bubble. Some porous surfaces also contain moisture, which can create bubbling if that moisture flows to the surface from extreme temperature changes.
• Spray equipment moisture. If moisture from the air gets into spray lines, it can cause bubbling in the coating because the isocyanate component will react with the moisture. Isocyanate will create CO2 and start to foam, which is how these pinholes appear once sprayed.
• Humidity. If you’re working in an environment with relatively high humidity, the moisture in the air can react with the coating after it’s sprayed and while it’s curing.

Solutions

The best way to avoid bubbles or blisters after applying a polyurea or hybrid coating is by following the manufacturer’s instructions. Double-check your equipment to ensure it’s proportioning the correct mix ratio before spraying.

If possible, work in a temperature-controlled environment. The best application temperature for most polyurea and hybrid coatings is between 65-100°F. Avoid coating in direct sunlight, high humidity, or rain to minimize moisture-related issues.

Performing a moisture vapor test on porous surfaces that may contain moisture is also recommended. Thoroughly clean and dry your application surface before coating to prevent adhesion issues. The method of cleaning you use will depend on the type and level of contamination on your surface. This includes solvent cleaning, power washing, or mechanical cleaning.

Another important step for porous surfaces is applying a primer. This can create a barrier that helps prevent trapped air and moisture from reaching the coating to cause bubbles. Primer not only seals the surface but also promotes better adhesion between the surface and the coating, which also prevents delamination. The surface should be coated as soon as possible after preparation to avoid further contamination.

Some blisters can be repaired by identifying the cause, removing them from the surface, preparing the surrounding area, applying a primer, and reapplying the coating.

Contact VFI if you have other issues with your polyurea or hybrid coating. Our technical team is available to help troubleshoot and find solutions to your problems.

How to Create Durable Foam Halloween Decorations

Since most Halloween and holiday décor or facades are meant for the outdoors, they must be strong enough to withstand the elements. The best way to create durable, weather-resistant props is with foam and a hard coat.

It is the combination of the lightweight, cost-effective foam and the durability of a hard coat that is so desirable for holiday attractions. The coating will resist weathering, chipping, and cracking in extreme conditions, keeping your foam projects intact through the holiday season.

What Kind of Foam Is Used for Holiday Props and Attractions?

Because most holiday props are only utilized once a year and not year-round, fabricators will typically want to use the cheapest materials possible while keeping up the durability of the piece to be used year after year. This is where EPS foam comes in.

It’s an easy-to-use and customizable material for various theming projects. Because you can shape it how you want, you can create realistic, life-like designs for haunts and haunted houses, Christmas extravaganzas, or other holiday events.

What Can I Use to Give the Foam a Hard Outer Surface?

The one additional thing you must consider when using foam is how you plan to protect it. Some DIYers might go straight to painting their props, but this can harm the foam, especially if you use solvent paint that could melt it.

Due to the environment your props may be situated in, you’re going to need a material that can protect them in harsh outdoor conditions. A polyurethane hard coat is the best material for the job due to its hardness, physical properties, and adhesion to EPS foam.

When the foam is sealed with a hard coating, it makes the piece resistant to weathering, water, impact, and other damage. These features keep your holiday props and decorations lasting for many seasons, whether they’re placed indoors or outdoors.

VFI has several hard coats to choose from, and while most small scene shops and set builders would choose a brushable coating due to its extended pot life and low equipment costs, there is a better alternative. Many people think that the only way they’ll be capable of spraying a urethane hard coat is with an expensive high-pressure spray rig, but there is a low-pressure version that works just as well and provides similar benefits.

VFI-6171 70 D Qwik Spray Hard Coat is a hard coating compatible with the VFI-7500 Qwik Spray Gun. These two items make up the Qwik Spray System, which is a low-volume, entry-level option for hardening foam. The coating can be used in indoor and outdoor environments as it is ASTM E84 Class A fire-tested.

A benefit of hard coats that some other materials fail to do is hold up to thermocycling. Because holiday seasons can be so unpredictable with temperature, you need to use a material that isn’t affected by such drastic changes. VFI hard coats are capable of enduring temperatures that go from high to extremely low without cracking. This not only keeps the hard coat intact, but it also protects your piece.

Benefits of Using a Cartridge-Based Hard Coat

While brushable and high-pressure hard coats offer their own benefits, there are several reasons why a cartridge-based system might benefit your project more.

• Fast-setting. Since cartridge-based coatings are sprayable, they come with similar benefits to high-pressure spray coatings. They offer curing speeds almost as fast as a high-pressure system, which is an advantage over roll and brush-on coatings. If you were to use a brush-on coating, it may provide you with an extended working time, but it will also extend the cure time as well. You won’t be able to start sanding or painting until the hard coat has fully hardened. A cartridge-based coating like VFI-6171 cures to handle in 5-7 minutes for same-day sanding and painting.
• Ease of use. As a cartridge-based system, VFI-6171 is easy to load into the applicator and start using once connected to an air compressor. VFI has even put together instructions on assembling and loading the applicator to make the process go even smoother. The applicator itself is portable, lightweight, and easy to maneuver.
• Minimal waste. There is virtually no clean-up necessary because the cartridges can simply be thrown away once empty. There are no spray lines to worry about flushing either since the static mix tips can be discarded as well. The only clean-up you need to be concerned with is potential overspray. You also don’t need to worry about mixing up material you don’t need since the exact ratio is contained in the cartridges. We’ve even made it easy to figure out how many cartridges you need by viewing the Qwik Spray coverage chart on the product page.
• Smooth, consistent finish. Bare, carved foam is notoriously hard to paint. A sprayable coating will provide a smooth, rigid surface that makes it much easier to paint the piece. Hard coating also makes it easier to create a more realistic, professional look when you paint over it. Since the coating is sprayed, you have more control compared to brush or roll-on applications. There’s always the risk of creating brush strokes or using too much material in certain places, which causes the coating to drip. Due to these defects, brush-on coatings will need extra post-work to achieve the finish desired.
• Minimize bubbling. A unique downside of urethane is that it is a moisture-sensitive material. This moisture sensitivity makes it harder to use in humid environments without causing bubbling on the surface, resulting in extra post-work after cure. However, when you use a spray coating, you reduce the risk of bubbles forming in the curing process because the material sets faster than a brushable coating.
• Lower long-term costs. If you’re a small fabricator and you’re using a brushable hard coat, you might want to consider upgrading to a cartridge-based system. Over time, material costs for a brushable hard coat are more expensive than the upfront costs for Qwik Spray equipment. If you’re consistently working on projects, you’ll make the upfront costs back in no time.

What Holiday Décor Can I Create with Hard Coated Foam?

With EPS foam as your base, there’s no limit to what kind of holiday décor and props you can create. Since sprayable coatings conform to the surface without diminishing details, you can create hyperrealistic pieces for all seasons, including:

• Set pieces – We’ve seen our hard coat used to protect large castle facades, architectural shapes, and archways, which work as spooky entrances to haunted houses and mazes.
• Small indoor or outdoor props – Small gravestones, pumpkins, snowmen, mushrooms, and more can make great accents to a larger themed space.
• Large indoor or outdoor props – Big, life-like props of skeletons can frighten guests in a haunted house, or giant ornaments can invite them into your winter wonderland.
• Photo opportunities – Larger-than-life statues of pumpkins, elves, reindeer, Easter bunnies, and more can make lovely photo opportunities for an entire family.

Contact VFI for more information on our hard coats for your next EPS theming holiday project.

Do I Need a Protective Coating for My Trailer?

Because trailers take a beating in transport, a protective coating is essential to keep them in good condition for the long haul. If you work with trailers daily, you know how quickly they can start to deteriorate.

Regardless of what you’re using the trailer for or the distances you’re going, several factors can damage the equipment over time. These damages can result from road hazards, weather conditions, accidental spills, or cargo wear and tear.

While it may be nice to keep the original steel, aluminum, or wood finish that most trailers have, it’s more cost-efficient to prevent repair or replacement down the line with a protective coating.

Best Coating Options for Trailers

Plenty of trailer coatings on the market can offer support, but the ones that provide unmatched protection are polyurea and polyurea hybrids. Each protective coating has its own benefits and drawbacks. Which one you choose depends on your needs and the type of trailer you’re protecting.

Polyurea

The type of coatings that everyone looks to first are typically polyureas. These are advanced materials with premium properties due to the raw materials used to make them. Due to their extremely fast cure speed, they are sprayed through high-pressure equipment. The benefit of this is you have a quick return to service once your trailer has been sprayed.

VFI’s most recommended polyurea for trailer protection is our general-purpose VFI-201 50 D Polyurea Coating. It has great adhesion with prepared surfaces and can be sprayed vertically and horizontally without sagging. With excellent physical properties, it’s made to last and hold up in the roughest conditions.

Polyurea’s moisture insensitivity is one of the factors boasted about the most. While that is important to consider, it isn’t always necessary. Their features and properties may seem worth the uptick in price, but they’re not the be-all and end-all for protection. They also aren’t the easiest to work with if you don’t have experience with them or high-pressure equipment.

Also, some manufacturers might say their coatings are polyureas, but it’s more likely that they’re polyurea hybrids in disguise. Check out our blog on how to tell the difference between a polyurea and a hybrid coating.

Polyurea Hybrid

Before you’re set on polyurea, determine if your trailer even needs it. If you’re not working in an environment where moisture is an issue, you can usually switch to a polyurea hybrid coating.

A perk of polyurea hybrids is they are a combination of polyurea and polyurethane, so they provide a good balance of performance, properties, and price. They also offer more application options depending on your processing needs. While they are typically sprayed through high-pressure equipment, they can be used in low-pressure and cartridge-based systems as well.

Like polyureas, hybrids have rapid cure times, allowing you to return your trailer equipment to service in as little as 4-24 hours. These spray-on coatings will typically also offer the same Shore hardness (around 40-60 D) for durable yet flexible protection. The only real negative effect of using them is that they are more moisture-sensitive. This means that they may bubble if exposed to too much moisture.

VFI manufactures several polyurea hybrid coatings for trailers:

• VFI-542 High Pressure Spray Bedliner is a standard high-pressure coating with a fine, durable texture for abrasion, impact, and slip resistance. It is almost 60 D Shore hardness with high tensile and tear strength.
• VFI-543 Low Pressure Spray Bedliner is the low-pressure version at a 40 D hardness for more flexibility to withstand cracking, warping, and peeling in extreme temperatures. It will provide a less fine texture on surfaces.
• VFI-544 Qwik Spray Bedliner is the economical Qwik Spray version used with the VFI-7500 Qwik Spray Gun to allow for easy, portable spraying. It will also provide a larger, less consistent texture on trailers.
• VFI-206 60 D Polyurea Hybrid Coating is a polyurea hybrid. It’s similar in hardness to VFI-542 but provides higher tensile strength, elongation, and tear strength for properties like a polyurea. Like other hybrid coatings, it protects against chemicals, impact, abrasion, and more. It sets very fast using high-pressure equipment, allowing you to spray it on vertical, horizontal, and even overhead surfaces.

Benefits of a Protective Coating

Both polyurea and hybrid coatings offer plenty of benefits for trailers, including:

• Extended service life. Probably the most important benefit of these coatings is their ability to extend the working life of your trailers. Because they are formulated to be durable with impact and abrasion resistance, they’re strong enough to ward off daily wear that causes cracks, tears, and peeling. Daily wear includes extreme weather like rain, heat, or snow and road hazards like rocks, dirt, salt, or chemicals.
• Rust and corrosion-resistant. These are the best coatings to protect trailer parts from rust and corrosion because they create a seamless, watertight barrier. The coating prevents water and other contaminants from reaching the original surface and causing deterioration. They also have chemical resistance, which prevents oil, fuel, and other chemicals from causing corrosion, stains, and more. This feature is especially useful if you are hauling livestock or sensitive cargo.
• Anti-slip protection. Applying a textured protective coating on the floor of any trailer can help prevent slipping and skidding. When you constantly haul cargo in and out of the trailer, you want the utmost safety for workers to decrease slip and fall accidents. The textured surface provides more grip, which also helps prevent cargo from moving around too much in transit. Some of VFI’s products provide increased anti-slip protection with a larger, more coarse texture.
• Sound dampening. The original wood and metal surfaces trailers are made of can be loud with cargo clinking around on the drive. A softer, rubbery coating will mute the sounds of shifting cargo and eliminate vibration noises. It will also help protect your cargo from bumps in the road.
• Improved aesthetics. While painting your trailer might improve the aesthetics, it will scratch and fade more easily than a protective coating. Not only is a protective coating functional, but it’s also fashionable. These coatings can transform new and worn trailers with a customized finish and various color options. Because they are scratch and abrasion-resistant, your trailer will also be protected from future scrapes, dings, and dents.
• Higher mils = better impact resistance. These materials are used as sacrificial coating as well, because of the amount that can be applied compared to a standard industrial coating. This allows for more resistance to wear and tear and greater impact resistance, providing more protection for the metal.

What Types of Trailers Can Benefit?

Because these coatings are sprayable, they can be applied to just about any prepared surface, no matter the shape or size. We’ve seen doors, floors, sidewalls, frames, wheel wells, and even entire trailers sprayed. The most common trailers that use protective coatings include:

• Open
• Enclosed
• Tag along
• Gooseneck
• Flatbed
• Boat
• Etc.

Contact VFI if you’d like more insight on the best protective coating for your specific trailer project.

Why Isn’t My Polyurea or Hybrid Coating Adhering to the Surface?

If you notice your polyurea or hybrid coating isn’t adhering to the surface, several factors could be the cause. Surface preparation, the environment, the application process, and recoating can all be reasons for adhesion failures.

Knowing how to work with these coatings is important for optimal performance and adhesion. Due to rapid cure times and the use of high-pressure equipment for most applications, it’s easy to make mistakes. Read the material technical data sheet (TDS) before you begin working to avoid issues.

Reasons Adhesion Failures Occur in Coatings

One of polyurea and hybrid coatings’ most desirable traits is their ability to create a strong, long-lasting bond. When they adhere, they provide long-term protection to the surface underneath. When they don’t adhere, they will peel off prematurely from the surface, negating any effect you should have gotten.

1. Poor Surface Preparation

The most common reason for adhesion issues is failure to prepare the surface before application. If you have a lot of ground to cover, it might seem easier to skip surface preparation and go right to applying the coating. A good application is completely reliant on the surface preparation that was done in advance.

If you don’t ensure that the surface is clean and free of contaminants, you may see bubbling and blistering in those areas. These defects will cause bonding issues and delamination.

Some surfaces have extra preparation requirements, which include sanding, grinding, shot blasting, making repairs, etc. Failure to properly prepare the surface will result in adhesion failure.

Also, not all surfaces are compatible with polyurea and hybrid coatings. Some require the use of a primer as a bonding agent to promote adhesion. Porous surfaces that contain moisture and aren’t primed can also cause adhesion issues through bubbling and blistering.

2. Environmental Extremes

While many manufacturers boast about polyurea’s moisture insensitivity, it is sensitive for adhesion. Just because it can cure over a block of ice does not mean that it can stick to the block of ice. And because polyurea hybrids are partly composed of polyurethane, they are even more sensitive. Most coatings require a dry surface to adhere effectively. Excessive moisture on the surface can cause blisters, pinholes, and peeling, which weaken the coating.

This is why it’s essential to make sure the environment and application surface have low or no moisture content. Moisture compromises the integrity of the coating and will cause adhesion issues.

Another environmental factor that can cause adhesion issues is temperature. It plays a big part in the coating’s ability to cure. If the surface, environment, and material temperatures are not in line with the manufacturer’s guidelines, issues will arise. The coating might not cure correctly in extreme hot or cold temperatures. Curing issues lead to bubbling, pinholes, peeling, and delamination.

3. Application Issues

Some coatings are fast-setting and harder to apply consistently without training. Coating speed is directly related to how long a coating has to bond to the surface to provide adhesion. The faster the coating the less time for adhesion to occur. To combat this issue, you can use a slower version with low-pressure or cartridge-based equipment that grants higher adhesion. Additionally, the thicker you spray or apply a coating the faster it will cure reducing your adhesion.

As two-component materials, polyurea and hybrid coatings have to be mixed at a specific ratio to cure. If the incorrect mix ratio is used, it will affect their strength and physical properties. A weakened coating will lead to poor adhesion. Inadequate mixing can also cause curing and adhesion issues. These are problems with the spray equipment that need to be corrected.

4. Missed Recoat Window

Apart from surface adhesion failure, there is also intercoat adhesion failure. Intercoat adhesion failure can occur when adding another coat to the surface. Failure typically occurs because the applicator has missed the recoat window. Once the window closes, you must apply a primer to promote adhesion between coats; otherwise, failure will occur.

Solutions

If your coating isn’t adhering to the surface, you will have to restart the application process. Always read the manufacturer’s instructions before working with polyurea or hybrid coatings. Ensure temperature and humidity levels are suitable for application, which is dependent upon your product. We typically recommend working between 50-90°F. If you’re working with a porous surface, it should be free of moisture or have a low moisture content.

Use a compatible cleaning agent or detergent to remove dirt, dust, oil, films, and more. Sometimes, a degreaser or pressure washer is used to make the process easier.

Specific surface preparation is going to depend on what surface you are applying the coating to. Some metal and wood surfaces might need to be sanded or scuffed. 40-grit sandpaper or a wire cup brush sander are recommended for applications like truck beds. For harsher surfaces, roughly sanding or sandblasting to SP6-SP10 to remove rust, mill scale, dirt, and more is essential. Repair damaged or cracked areas to ensure a smooth surface for coating.

For increased adhesion, use an approved primer. VFI’s recommended primers are VFI-#11 9:1 Epoxy Primer, VFI-1016 Steel Primer, and VFI-1017 Porous Surface Primer. Which one you use will depend on the surface type. They will form a bond between the surface and coating to ensure a strong and durable finish.

Optimize your adhesion based on your application. There are specific instances where speed is not as critical, and you are able to use a slower coating. Anytime you can go slower you will gain more adhesion. VFI does have formulas that are optimized for adhesion, and they will usually be slower than a 10 second gel time.

When spraying the material, ensure that your equipment is calibrated to the correct mix ratio. Also, ensure that it can get up to the recommended temperature and pressure outputs. This will ensure a smooth application and promote better adhesion.

It should then be applied in a continuous, even layer. Stay within the recoat window if you are applying layers to build thickness. If you miss the recoat window, prime or prep the surface to ensure adhesion based on recoat instructions.

Contact VFI if you are experiencing other issues with polyurea and hybrid coatings.

Why Is My Urethane Rubber Mold Sticky?

Some urethane rubber users have come to us and are confused as to why their rubber is sticky after waiting for it to cure. Others have mentioned having a hard time removing it from the mold box or form as well.

If the material itself is sticky, it may not have been mixed thoroughly enough before it was poured. If it’s clinging to the mold box or form, then not enough mold release was used to prevent it from sticking to the surface.

Reasons Rubber Molds Might Be Sticky

Mixing is typically where the biggest mistakes are made. Just because the material might look fully mixed in the bucket doesn’t mean it is. Poor mixing generally occurs because users are concerned about the pot life of the material, so they’re not mixing for long enough.

Some mold makers use large amounts of rubber with short pot lives, and that causes them to rush and skip vital steps. They end up with a bad mix, which wastes time and material.

Also, scraping the sides of your mixing container while pouring the rubber into a mold can cause these sticky spots. It’s harder to thoroughly mix material that is stuck on the sides or at the bottom of the container, which creates excessive amounts of the A or B side material.

Excessive amounts of A side material will cause sticky or tacky spots that may dry eventually. However, if they dry, that doesn’t mean the rubber will last as long as it normally should. It might feel softer in these areas and could tear more easily in the casting process. Excessive spots of B side material will never dry.

On the other hand, if your material is sticking to the mold box or even the master models, it probably wasn’t released or sealed properly.

Non-porous surfaces always require the use of a release agent. If you’re casting urethane rubber over porous surfaces, those surfaces have to be sealed and released to prevent adhesion from occurring.

If adhesion does occur, it could potentially break the master. Keeping the master intact is important, especially if it is delicate. Using enough release should prevent this from happening. Release is also needed when casting into the urethane mold as well. Check out VFI’s release tech piece for more information.

Note: Cure inhibition can also cause stickiness, but it is unlikely that this is a cause for liquid urethane rubber molds. Cure inhibition is a much bigger problem for tin-cured silicone rubber.

However, one material that should be avoided when making any rubber mold is sulfur-based clay. Anywhere the clay touches will not dry, so it will be sticky.

Solution

If your initial mix has already been left to dry at room temperature for days and it’s still sticky, there’s nothing you can do to fix it. The best thing you can do is restart with a new batch of material.

The important thing is that sticky spots in your urethane rubber will typically not ruin the master models. If the rubber ruined your master, it would create even more work for you. It’s much easier to purchase more material and start over than it is to make another master.

Use the double bucket mix method. After mixing in one container, transfer the material into another clean mixing container to mix again. Doing this will ensure a thorough mix, so you won’t have to worry about your molding rubber being sticky.

Always scrape the bottom and sides of the container while you are mixing. Unmixed material can cling to those hard-to-reach areas.

For mixing larger amounts of material, use a mechanical mixer. If you try to hand mix more than a gallon of material, you will be unable to mix it thoroughly enough before the pot life ends.

Using a release agent will protect and extend the life of your mold. Always use the correct type of mold release and the right amount.

If you’re molding over a porous surface, VFI recommends using a mixture of 80% mineral spirits to 20% petroleum jelly by weight to seal it. Then, you should also spray the entire molding surface with a silicone-based release agent like Chem-Trend Mr-515 Aerosol to further prevent the rubber from sticking to the mold.

Contact VFI if you have further questions on preventing urethane rubber issues. If your urethane rubber mold is not drying, read our other tech piece here.

Liquid Rubber for Concrete Stone Molds

Ensuring you have the right liquid rubber material to make concrete stone molds is important to the success of your project. If you choose just any rubber to make your mold, it may result in damage to your casting or even the mold itself.

Artificial stone castings are not like any concrete project. You wouldn’t use the same rubber for a large formliner or stamping project. Because these materials are more delicate and detailed, they require material that can accommodate the complexity of the original design.

Polyurethane rubber is one of the best molding materials for these applications because of its abrasion resistance. It will hold up to repeated concrete casting without deteriorating quickly. However, as a versatile material, there are many formulas to choose from. You’ll need to look into the material properties to determine the best one for your concrete stone project.

What Properties Affect the Rubber You Choose?

Urethane rubber comes with a handful of important properties that you should look into, including:

• Shore Hardness – A standard tool called a durometer is used to determine a material’s resistance to deformation or indentation. The number tells you whether the rubber will be very soft, hard, or somewhere in between. Typically, for concrete stone projects, you will want to look at rubbers with a Shore hardness below 55 A. If you tried removing a delicate piece from a harder mold, you would most likely see some breakage from the force used to remove it. This force could ruin your casting and your mold. It could also break your original model when removing the mold from the mold box. While hardness is an important property, it’s not the only one that affects the function of the mold.
• Tensile Strength – This property determines how much force it takes to stretch a material before it breaks. Concerning Shore hardness, tensile strength tends to increase as the hardness increases. Having high tensile strength is important when making larger molds so the mold will hold up to large pours of abrasive materials. Molding rubbers with a hardness between 25-55 A will have a lower tensile strength. This isn’t as much of a concern for concrete stone molds, as the mold must be made with thicker walls to ensure durability.
• Elongation – This property determines the length the material can be stretched before it breaks. The elongation of a material is closely related to how flexible it is. Typically, lower durometer rubbers will have better elongation than higher durometer rubbers because they have better flexibility and stretchability. Since concrete stone molds need good flexibility, this would be an important property to consider.
• Tear Strength – This property determines the force needed to initiate a tear. It can be important for some molds if they are roughly handled in the demold process. Big molds or formliners that make concrete panels can tear more easily due to the pulling force initiated by the removal of the casting, which is why they require good tear strength. Because smaller concrete stone molds aren’t normally put through as much stress when demolding, tear strength is less important.
• Flexibility – This isn’t a property with standard testing; it is more so determined by the results of other properties, such as tensile strength and elongation. It’s also related to Shore hardness because if the rubber has a lower hardness or is softer, it will be more pliable. The most desirable thing about a flexible rubber is that it is better at capturing finer details that rigid molds might not be able to. The flexibility is also directly related to how thick you are pouring the rubber. A thinner pour will make a harder rubber more flexible. This is an important feature for most stone mold projects.

Why Use Urethane for Concrete Molds?

Urethane is a desirable material when casting concrete because it has a good variety of properties. These molds will typically be the most durable because of better tear strength and elongation. They also take less skill to make since they are a pourable formula.

They’re a more cost-effective alternative compared to making pourable molds out of materials like silicone. They are extremely reusable, as they can handle the abrasive effects of concrete. You can produce exact replicas of hundreds of artificial stone pieces from a single mold as long as the mold is properly cared for. You also don’t have to worry about shrinkage like you would with a latex mold.

Some silicone rubbers are more desired because they can be brushed onto surfaces to produce the highest detail possible and do not require release from stone. The problem is that it takes a lot more time to make these molds. Plus, they will always need to be backed with a mother mold for support when casting. So, if your concrete project doesn’t have certain requirements that prevent urethane and release from being used, a urethane mold is the way to go.

What Can Low Durometer Concrete Stone Molds Produce?

Liquid rubber is prized for being a versatile material because it can meet your design specifications. There’s not really a limit to the kinds of concrete elements you can produce, including:

Cast Stone

These elements produced from urethane molds are architectural building materials made to look like natural stone. They will typically be 3-dimensional decorative blocks, flat pieces, or other ornamental structures. They add beauty and dimension to homes, commercial buildings, gardens, parks, and plazas. Cast stone is only made for decorative purposes and will not usually offer structural support.

The rubber mold is produced from original stone pieces in the shape of quoins, keystones, cladding, window surrounds, corbels, columns, pillars, coping, capping, and more. Liquid rubber allows you to create a number of the exact same casting and is great for highly customized projects too.

VFI typically recommends using a rubber with a durometer between 25-40 A. Using a softer rubber is crucial for these projects because it ensures easy and complete removal of the casting from any intricate details, shapes, and undercuts without tearing or sticking to the mold.

Manufactured Stone

Manufactured stone castings are 3-dimensional, but typically flat-looking architectural elements. They are also called stone veneers as they are a thin layer of concrete used to decorate the exterior or interior of a building or structure.

These are not stand-alone products. They are applied to a surface like a concrete or wood wall, fireplace, or outdoor kitchen to create or match a desired aesthetic. They can easily be pigmented and will mimic the details of slate, limestone, granite, and other natural stones.

VFI typically recommends using a rubber with a durometer between 30-60 A. These molds are best for mass production of artificial stones. Unlike natural stone, these molds create a standard, repeatable pattern for homes, buildings, and other structures.

Architectural restoration

Architectural restoration projects are the replacement of natural stone pieces on historic buildings. They are extremely delicate, which is why most mold makers choose to use latex or silicone. These rubbers can be brushed onto surfaces to make a mold and do not adhere to the surface like urethane would.

However, VFI has developed Max Release Urethane Rubbers for these exact projects. In the past, you would have had to use enough release to ensure the rubber would demold from the architectural element. With this new formula, less release is required, and you won’t have to worry about damaging the original piece.

Apart from best-in-class release characteristics, the Max Release line also offers premium properties. These rubbers range in durometers from 25-50 A and help minimize damage during the casting process. They put less stress on the casting, allowing for breakage rates as low as 2-3%. So, you protect your castings and make the mold last longer for less material waste.

How Do You Prepare Concrete Stone Molds?

Models used to make urethane rubber molds typically need to be prepared differently than silicone or latex due to their release characteristics. Determine if your model needs to be sealed before you begin the molding process. Porous surfaces will need to be sealed with something stronger than release.

Since most models used to make stone molds are porous, you must seal the stone beforehand. VFI recommends using a combination of 80% mineral spirits to 20% petroleum jelly by volume. Several layers of the sealer should be applied before pouring the molding rubber.

Also, a release agent must always be used on any surface to ensure urethane demolds without issue. Apply the release agent to your model, mold box, and mold when casting.

Contact VFI if you need help choosing the best rubber for your concrete stone mold project.

Why Is My Urethane Mold Deforming?

So, you’ve done everything right in the process of making your mold, but after you’ve demolded it, it’s begun to deform. We’ve seen this happen to urethane rubber users periodically, and there can be several reasons this defect occurs. The biggest reason is time. You’re either demolding your mold or casting into it too quickly.

How you make the mold, use it, and store it can also affect its ability to hold shape over time. Once a mold becomes deformed, its usability is greatly reduced. This leads to a shortened lifespan, which increases production costs and downtime from having to remake the mold. The best way to maintain your mold is by reading the technical data sheet (TDS) and adhering to the instructions and guidelines listed by the manufacturer.

Reasons Your Mold is Deforming

1. Demolding Too Early

Many factors affect how fast your mold cures, including temperature, mold wall thickness, mold size, etc. If you don’t adhere to the recommended guidelines when making your mold, the pot life and demold time can change. If you lose track of them, you may run into issues.

If you demold too soon, the rubber might not have hardened enough to maintain its shape, causing it to warp or deform when you remove it from the mold box. Early removal can also cause damage because it is soft and prone to tearing. Even if the mold seems cured on the surface, it probably hasn’t cured internally.

At this point, since the mold is distorted, your future casting probably won’t be an accurate representation of the original object. If you want to demold it faster, you’ll have to use a faster material.

2. Casting Too Soon After Demolding

Many newer polyurethane users think that once the mold can be demolded, it’s ready to use. However, if you use it right after you pull it out of the mold box or form, you can deform or distort it.

Urethane initially cures after 16 hours and can be demolded, but it still needs to develop the necessary strength for various casting scenarios. Most manufacturers will recommend an additional waiting period after demolding before you use the mold. For products with demold time of 16 hours it is recommended to wait 72 hours.

Note: The longer you wait to cast into your newly made mold, the stronger it will be. Urethane develops full physical properties after 7 days. If you don’t want to wait, heating the mold can typically increase its physical properties faster.

3. Not Storing the Mold Properly

If you aren’t casting into your mold for a length of time, you’ll probably want to store it for later use. Do not store it vertically or on its side. Urethane can distort if it’s not stored on a flat surface. If a corner is curled, the mold is on top of another object, or something is lying on top of it, it may never go back to its original shape.

Also, don’t store it outside or in direct sunlight. Elevated temperatures and UV rays can negatively affect the mold. This may prevent you from getting accurate castings the next time you use it because the mold may have shrunk, expanded, or degraded.

4. Using the Mold in Extreme Temperatures

The type of deformation extreme temperatures cause will not ruin your mold, but it will change its shape. These extreme temperatures cause the mold to change because the rubber will expand and contract with the weather.

In most cases, this change might only be temporary. If the mold has expanded, it’s probably due to high temperatures, but if it has shrunk, it’s probably due to low temperatures. Dimensional changes often occur because you are not using the mold in the same conditions that you made it.

If you are constantly working in extreme temperatures, your mold may never return to its original size. This results in your castings being an inaccurate representation of the original model(s).

Note: Some solvent and oil-based release agents can also cause your urethane mold to expand. Unlike temperature, this will deform the mold permanently and cannot be reversed.

5. Mold Design Does Not Accommodate the Casting Material

Before you even begin to make your mold, you need to consider the design, what materials you are using to make it, and what materials you will be casting into it.

The thickness of your mold walls plays a big part in preventing your mold from distorting. We know you want to save money on material costs, but if you don’t make your walls thick enough, they may bulge in the casting process. Molds with complex shapes are prone to warping as well.

If you’re making a mold with thin walls, you must be sure it will hold up to the material you’re casting into it. Materials like concrete are heavy, and if your mold isn’t strong enough, it will distort during the casting process.

The hardness of the mold can also determine how it might deform if not designed well. If you use a softer rubber (25-45 A), you cannot pour the walls thinner than ¾ – 1 inch thick. Otherwise, it might not accommodate the weight of the casting material, especially if you are casting something big.

Also, thinner areas of the mold can take longer to cure. You might think you’ve given your mold enough time before casting, but it takes a little longer for thinner parts to gain the strength necessary to do so.

Solutions

Take your time, and don’t rush when demolding your newly made mold or casting into it. Check the manufacturer’s TDS to be sure you are following recommended cure times and temperatures.

When making the mold and casting, do so at room temperature (77°F) for the best results. All VFI products are tested with properties obtained at room temperature. Anything outside of that temperature will change the pot life, demold time, and dimensional stability of the rubber.

VFI recommends leaving your demolded urethane mold on a level surface at room temperature (77°F) for an extra 3 days. This will maximize the performance of the mold and allow it to gain enough properties for casting. You’ll be able to repeatedly cast into it without worrying about distortion.

A good rule of thumb is to use a harder rubber when making large castings. This way you can make the mold walls thinner because the rubber will have more tear resistance and can support heavier loads. On the other hand, if you use a softer material, make the mold with thicker walls to help cure it quicker and to give it additional structural support.

Urethane will cure quicker in thicker areas. Be sure you’re following the thickness requirements recommended by the manufacturer to withstand the pressure of casting materials. VFI’s recommended wall thicknesses are listed on every TDS. If you’re pouring under what’s recommended, you’ll need a rubber with a higher Shore hardness.

Since urethane rubber is meant to be reusable, you want to do everything you can to keep using it. The best way to extend the life of your mold is with proper care and storage. That means when you’re not using the mold, you want to store it flat, in a dry, temperature-controlled location, away from direct sunlight.

Do not stack urethane molds on top of or underneath other molds. They might stick to each other, which will require force to tear them apart and weaken the rubber. If you store them in contact with molds made of different materials, this can cause swelling, shrinking, and distortion from the transferring of oils or plasticizers.

Contact VFI if you are still having problems with your urethane mold distorting or if you have other technical issues.

Why Can’t I Remove My Casting from My Urethane Mold?

Some urethane rubber users have run into issues with being unable to remove their concrete casting from their mold. Major reasons this occurs is because a release agent was not used or not enough of it was used to prevent unwanted adhesion.

The casting will stick to the mold, which may lead to the piece breaking or the mold tearing if you have to use excessive force during the demold process. Overall, this results in increased breakage rates, material waste, production loss, and possible loss of the mold.

Reasons Why Your Casting Isn’t Demolding Properly

Reason #1: Not Using Mold Release

Urethane rubber is a unique molding material because of its adhesive characteristics. Unlike silicone or latex, it will adhere to anything. You need to create a barrier by using a release agent so it won’t bond with the surface of the casting.

If you do not use a release agent, you probably won’t be able to get your concrete casting out without breaking it. The adhesive effects of the concrete will also wear or tear your mold making it unusable.

Reason #2: Not Using Enough Mold Release

There’s a fine line between using too much and too little mold release. If you give your surface a light coat or mist of release, it might not be enough to prevent adhesion from occurring. If the mold has complex details or undercuts, you might miss some spots, which allows certain parts of the concrete piece to get stuck.

A torn mold can result from not using enough release because the concrete sticks to and pulls on the mold during removal. If your mold tears when you are demolding, you’re using too much force and stretching it beyond its limit to break the bond.

It’s also important to wait for the release agent to dry before you start casting. Once it is dry, it creates a smooth, effective barrier on the mold surface. If you don’t wait, the release agent might mix with the concrete, preventing the release agent from forming a barrier. Waiting also prevents residue from transferring onto the concrete, which could cause imperfections.

Reason #3: Using the Wrong Mold Release

If the specific release agent you have chosen is incompatible with your polyurethane mold or the concrete you’re casting, it can cause demolding issues. The casting may stick to the surface, tear the mold, or cause imperfections on the surface. Most release agents specify which materials they are compatible with, so it’s important to read the manufacturer’s instructions. Most solvent or oil-based releases will cause issues with urethane.

Reason #4: Choosing the Wrong Mold

Some key things to consider for your concrete casting project are the rigidity or flexibility and the complexity of the mold, including shape, size, details, etc.

You will typically have an easier time removing concrete castings from flexible, less complex molds. If you choose a firm rubber for a project with intricate details or undercuts, you might have trouble removing the casting, resulting in breakage. While most liquid rubbers stretch, over-stretching can cause tears in your mold.

Reason #5: Demolding Too Soon

Sometimes, issues with demolding are as simple as not waiting long enough for the concrete to cure. If the concrete doesn’t have enough time to gain its inherent strength before you demold it, it may be fragile and could break in the process. It also might still be sticky and leave residue in the mold that needs to be cleaned out.

Reason #6: Pigment

Depending on the casting, you may need to use pigment, and depending on the pigment, it can make it harder to demold. There are two styles of pigment, a powder and a liquid pigment. VFI always prefers the use of powder pigment over liquid pigment, because the liquid pigment is usually used for stamps and contains solvents that will attack the urethane rubber. Once the liquid pigment attacks the urethane rubber it will bind the concrete to the mold surface.

Note: Liquid pigment in concrete does not cause the same issue as applying liquid pigment to the surface of the mold.

Solutions

Always read the manufacturer’s instructions before using a product. They can be found on any product page or technical data sheet.

• Make sure you apply a release agent and use the correct kind. Using one will extend the life of your mold and decrease breakage rates. When casting concrete into a urethane mold, VFI recommends using one of Chem-Trend’s water-based releases specifically designed to release these materials from each other. We’ve seen great success with the dilutable CR-19597. The release agent should be applied before each cast to ensure the next one will demold without issue. Do not use an oil-based or biodegradable release, as these can cause the rubber to expand.
• Make sure you’re evenly coating the surface with a release agent, especially in complex and detailed mold areas. You need to find a balance where there’s enough on the surface to make the casting demold with ease but not too much so that it will make the surface shiny. VFI recommends spraying a few coats of a light mist over the mold. Allow the release agent to dry in between each coat and before casting. Consistent reapplication will also help prevent underuse.
• Use a Max Release urethane molding rubber. VFI released a series of low-durometer rubbers that have enhanced release abilities comparable to silicone. The benefit of using these rubbers is that you don’t need as much mold release on the rubber, and less effort is required to demold your casting. Since their hardness ranges from 25-50 A, they also provide better flexibility, allowing you to make more detailed castings without worrying about breakage. Check out the press release for more information.
• Allow the concrete to cure fully before removing it from the mold. The longer you let your material sit in the mold, the longer it has to gain strength. It can typically be removed within 24-72 hours.
• Go slow when removing your casting. People want the demold process to be quick and easy, but depending on the size of your casting, it might take more time and effort to get it out. Additional care should be taken if your casting is extremely detailed because you don’t want those details to break off when you pull the rubber away. Carefully work the edges of the mold to reduce the stress put on the rubber. Do not pull or twist the mold harshly.

Note: For increased reusability of your concrete mold, clean it after each use. Warm, soapy water is typically the best way to clean a urethane mold. It will remove residue and particle buildup, so you start with a clean surface when you’re casting next.

Contact VFI if you’re still having trouble demolding your concrete project so we can assist you.

Why Is My Urethane Rubber Mold Not Drying?

VFI has had customers using two-component urethane rubber come to us saying their material is not drying or curing. From experience and testing, we know this is typically an issue with mixing, mix ratios, or temperature.

To dry or harden liquid urethane, you must measure and combine a precise amount of each liquid component (A and B sides) before mixing thoroughly. The exact combination of materials is the mix ratio, which also helps the material achieve its formulated properties. It can be expressed by weight and/or by volume.

After mixing and once poured into a mold box or form, the material should be left to dry for at least 16 hours at room temperature (77°F) for best results.

Reasons Liquid Rubber Might Not Cure

Do not assume all mix ratios and mixing instructions are the same. The mix ratio varies per product because each material’s precise mixing formula provides the desired performance characteristics and allows it to dry.

If you mix with too little Poly (B side), the material can feel brittle and not as strong. If you mix with too little Iso (A side), the material can feel too soft, tacky, or gooey to the touch.

A change in final properties may occur from using too much or too little of one material. The off ratio mix may also be softer (lower hardness) than it was formulated to be.

Insufficient mixing can also cause drying issues. While some areas of the rubber may harden like normal, you may see tacky or soft streaks that are excessive amounts of A side material or excessive amounts of B side material. Also, it’s important to always premix your B side material to ensure you have an even weight per gallon. This makes it easier to achieve a uniform mix overall.

Also, temperature can play a huge role in the material’s ability to dry. Urethane rubbers cure best at room temperature (77°F). If your material, work area, or molding models are too cold, the mold rubber will take more time to dry. In some cases, it may not dry at all.

It’s important to read the product technical data sheets (TDS). The TDS includes mix ratios, mixing instructions, and molding guidelines. This information helps ensure you’re using the correct amount of each component, working in the best conditions, and mixing thoroughly to prevent drying issues.

Solutions

The best thing you can do if your urethane rubber isn’t drying is to start over. If it hasn’t dried after at least 3 days sitting at room temperature, odds are it never will.

One of the things you can do to limit issues is to pour your A side (Iso) first. It’s better to add more Iso than it is to add too much Poly (B side). If your mix is heavy on the Poly, you’ll never get the rubber off the master or out of the mold box.

An important thing to note is that tacky or sticky material should not ruin your master if the rubber is Iso-rich, and it will be reusable. You won’t have to restart the entire mold making process, which is a win.

To ensure that your material will dry in your second attempt, adhere to precise mix ratios. If you deviate from the suggested mix ratios, whether by volume or weight, your material will not solidify or reach its formulated properties.

Depending on your application, you may benefit from using a mix ratio by weight over a mix ratio by volume, or vice versa. Measuring by weight can have more accurate results as long as you use a working scale.

Bring the material to at least 65°F before use. Work in room-temperature environments with room-temperature equipment when possible.

VFI also recommends using the double bucket mix method when combining liquid rubber. Rather than mixing in a single container and then pouring, you should mix in one container and then pour the material into a clean container to mix again. This is the best way to ensure that unmixed material in the first mixing container will not appear in your final product.

The material should be left for a minimum of 16 hours before demolding. After demolding, allow the rubber to sit for 3 days before use. It will take at least 7 days for the material to develop final formulated properties. If the material is left to dry at lower temperatures, it may take longer.

Sticking to these guidelines will provide the best, most consistent results when pouring urethane molding materials. Plus, it will save you time and money if you don’t have wasted, unusable material.

Contact VFI if you have any further questions on the urethane rubber drying process. If you’re wondering why your urethane rubber mold is bubbling, check out our tech piece here.

Do I Need to Use a Release Agent with Urethane Rubber?

Release agents are required for any application when making a two-part urethane rubber mold to prevent the materials from adhering together. Urethanes have inherent adhesion, which means they stick to just about anything. They will chemically and mechanically lock without release. You would have to use extensive force to break them apart, which could likely tear the mold and break your masters.

A release agent will create a barrier between the liquid rubber and the molding surface. This allows the mold to release easily from the mold box and masters.

What Can You Use as a Release Agent?

The release agent you use when making a mold will depend on the materials you are working with. The release should be specifically formulated for your molding application. Most will be labeled with a list of materials they are compatible with.
When the appropriate material is used, it aids in the demold process, helps produce quality molds, and increases the working life of the mold. There are several types available, including:

• Water-based – environmentally friendly and suitable for a wide range of materials.
• Solvent-based – ideal for use on molds exposed to high temperatures and pressures.
• Silicone-based – versatile and compatible with various materials. When making urethane molds, silicone-based agents are typically used.
• Silicone-free – preferred if silicone interaction is a concern.

How Can Your Rubber Mold Benefit from Using Mold Release?

• Release agents make it easier to remove a newly made mold from a mold box or form. This ease prevents your mold from tearing in the demold process, preventing rework and material waste. An intact mold is important for manufactured stone and advanced detail form liner projects.
• You can also preserve the masters you are using, as these may be more delicate than the material you will be casting to make replicas. The release prevents breakage of the original piece for future use if you have to make new molds.

What Are Some Best Practices for Releasing a Mold Box?

First, use adequate personal protective equipment when making your mold. Gloves, safety glasses, and long sleeves can prevent skin and eye irritation. Follow safety guidelines and instructions provided by the manufacturer.

When making your molds, ensure that your molding surface is clean and dry. Dirt, debris, and other contaminants can affect the function of the mold release and the quality of the mold. The contaminants can transfer over to the finished surface when you begin casting.

Prepare the model(s) you are molding around. Determine if you need to use a sealing agent. Porous surfaces like wood, concrete, stone, plaster, etc., must be sealed first. This will prevent the urethane from penetrating the porous model(s). Allow the sealer to dry before applying release.

Different mold releases can be sprayed, brushed, or wiped onto the mold box or form. Typically, the best method is spraying (aerosol), especially when coating large mold boxes or forms. Brushing on liquid release can be suitable for small projects and detailed areas. However, it’s easy to overapply using this method.

You’ll want to apply several coats to ensure your mold releases from the details on the model(s) with ease. Allow the release to dry before applying another and before you begin pouring the rubber. Also, avoid touching the surface until it has dried, as this could cause defects in the mold.

After demolding, clean the mold with detergent or solvent to remove residue from the mold box or form. This will ensure that is ready for use when you begin casting.

What Are Common Issues When Making the Mold?

When making a urethane mold, do not use a water-based release, as urethane is sensitive to moisture and will bubble. We also recommend avoiding the use of shellac. We’ve seen issues with this material where users will also apply another solvent or mineral spirits, which makes the shellac soft. When the rubber is poured, it will bond with the shellac and fail to demold.

Avoid overapplying the release to the point where it is dripping or pooling. Using more is not better and can affect the quality of the mold. Common problems with overuse include air bubbles and a glossy finish. That glossy finish will then transfer over to your future castings.

What Release Agents Does VFI Recommend When Making the Mold?

VFI recommends the silicone-based MR-515 Mold Release for non-porous surfaces when making urethane molds. Sprayable materials are the easiest and least time-consuming to use.

Shake the can and hold it about 8-10 inches from the molding surface. Spray evenly in a sweeping motion to prevent unwanted adhesion. Generally, you should apply a few coats before pouring the rubber. This will protect and extend the life of your mold.

If your models are porous, use a sealer before the release agent. We recommend a combination of 80% petroleum jelly to 20% mineral spirits by weight to seal those surfaces. Apply several coats of the sealer with a chip brush. Wait for each coat to dry before applying another. Then, apply a light mist of MR-515 over the model(s) and the non-porous areas of the mold box or form.

Some polyurethane rubbers require less release. This is a desirable feature for projects like architectural restoration since using a certain amount can diminish intricate details. VFI offers a line of lower durometer urethane rubbers with enhanced demold characteristics. They are the closest you can get to silicone release properties in a urethane.

Check out our press release for more information.

Contact VFI if you need further assistance with mold release for urethane rubber.

Why Are There Bubbles in My Urethane Rubber?

We’ve come across urethane rubber users in the past who have wondered why there are bubbles in their molds. Bubbles can present themselves in urethane rubber for various reasons, with the biggest one being moisture.

Polyurethane is a very moisture sensitive material, so if it finds its way into your mold-making process, it can create issues. The good news is that most moisture sources that cause bubbles can be controlled.

Reasons Bubbles Form in Urethane Rubber

Bubbles that appear in your finished piece can diminish details and transfer over to future castings, which is why it’s important to prevent them from forming. The following should be avoided:

1. Humidity

Working in a hot, humid environment is not good for your rubber material. The second you open the A (Iso) and B side (Poly) containers, moisture will try to find its way in. The longer these materials are left to sit, even when unmixed, the more they will absorb moisture.

Humidity can be especially detrimental if the material has a long working time. If your rubber is left to cure in these conditions, the material will continue to react with the moisture in the environment, which will lead to foaming or bubbling. These defects will then remain in the rubber once it has dried.

2. Wet Molding Surface & Porous Masters

Again, because urethane is moisture sensitive, if you see bubbles on the surface of your rubber once you’ve demolded it, it means that something was on the surface that caused it.

If your molding surface is wet or you’re using porous masters (plaster, concrete, gypsum, etc.) without properly sealing them, you might discover bubbles on the surface of the rubber.

3. Wet Mixing Equipment

If your mixing equipment (buckets, mixing sticks, etc.) is wet when you pour your material into it, a moisture reaction will occur. You will notice air bubbles begin to form while you’re mixing.

Air bubbles can also form based on your mixing procedures. If you mix too quickly or for too long, you may introduce more air into your mix. If this happens, pour your material slowly in a thin stream to allow those air bubbles to pop, or degas the material before pouring.

4. Excessive Mold Release

If you see surface defects like tiny pinholes or champagne bubbles in your rubber, you may be using too much mold release. You may also not be waiting enough time for the release to dry before you start casting.

Alternatively, the mold release you’re using could be past its expiration date or poorly mixed, but this will appear as indentations in the rubber and not air bubbles.

Solutions

Always check the technical data sheet for recommendations before using the material. The best thing you can do to avoid bubbles in your material is to work in a room temperature-controlled (77°F) environment. You want the relative humidity to be as low as possible.

While vacuum degassing and pressure potting can be useful in certain mold-making scenarios, it’s not always possible, depending on how much material you’re casting and the size of the mold you are trying to make.

Before you mix and pour the material, make sure your forms and masters are properly released and sealed. VFI recommends sealing porous surfaces with a mixture of 80% mineral spirits to 20% petroleum jelly.

Some people have used polyvinyl acetate (PVA), or Shellac, to seal their masters. However, it is easy to remove it from the surface accidentally. So, if you forget to reapply it, your masters will not be sealed, leading to various issues.

Once any porous surfaces are sealed, you must apply a compatible release agent. VFI recommends Chem-Trend MR-515 or a similar silicone-based release for urethane rubber. Do not use a water-based release agent.

Avoid using too much release and allow it to dry before you pour your rubber. If you use too much release, bubbles may form, or the surface might appear glossy, which will then transfer over to future castings.

Use dry mixing equipment. Plastic and metal mixing equipment is less likely to hold moisture. Mix slowly so you don’t generate more trapped air in the mixture. Once fully mixed, pour it slowly in a thin stream into the lowest point of the form to minimize the formation of air bubbles. Let it flow naturally into the rest of the form.

Avoid repeated opening and closing of the containers as this can also introduce moisture into the A and B side materials. If you plan on storing unused material, you must nitrogen purge each material and close the containers as soon as possible after use. Store the containers in a cool, dry place.

Contact VFI if you have other mold-making issues or check out our other tech pieces.

How Much Liquid Rubber Do I Need to Make a Mold?

Before making a mold, the most important thing to consider is how much liquid rubber you’ll need. Several factors will affect the amount, including the complexity, depth, width, and length of your model(s). Also, consider how thick you want to make your mold to ensure longevity and reusability.

If you use too much rubber, you’ll end up wasting material, but if you use too little, you may run out during the mold-making process and have to scramble to mix up more.

Before you can begin estimating, the first step is making a mold box or form. You must determine how far apart to place your models if you’re molding over multiple objects and the overall mold wall thickness. Then, you’ll have a better understanding of the empty cavities that need filling.

Why Mold Thickness Matters

Mold wall thickness is a critical element in the design of your urethane mold. It considers the thickness of the sides and bottom of the mold. How thick you should pour the rubber is determined by if the mold is going to be supported in a mold box and the number of incuts and intricate details that are present.

All VFI molding rubbers have a minimum pour depth that can be found on our TDI specification sheet or the individual technical data sheet (TDS) for each product. Follow these specifications to have the necessary tear strength of flexibility for proper demold and use of the mold.

Lower durometer rubbers (20-60 A) are softer and more flexible, which is why they must be poured thicker. If they are poured too thin, they can be weak and prone to tearing. They are recommended to be poured ¾ of an inch to 1 inch thick. Molds made of these rubbers are typically used for cast stone and manufactured stone projects.

A thicker mold will prevent the mold from deforming during the casting process and increase tear resistance. Thinner walls might make a flexible mold bulge from the pressure of the casting material. The castings created will not be exact replicas of the original. To prevent this, you would need to build a mold box to keep the mold from deforming.

As the rubber’s durometer increases, the minimum pour thickness decreases. The material is less flexible but will have good tear strength. These higher durometer rubbers (70-90 A) are typically best for larger precast concrete projects like formliners, stamps, or rollers.

Thinner pours (between 3/8 of an inch to ½ an inch) use less material, which also keeps material costs lower. They can be very large, which is why mold makers want them to be as light as possible for easier handling during the casting process.

Note: Thinner pours of urethane can take longer to cure. When less material is used in certain areas, it creates a smaller exothermic reaction. The less heat generated, the slower the material will cure.

Also, as a rule of thumb, we generally recommend pouring at least half of an inch above the tallest point on your master. This will create a thick enough mold bottom that withstands the abrasive effects and weight of materials like concrete.

How To Calculate Mold Size

Once you’ve determined how thick you need to make your mold walls, you can assemble your mold box and find out how much material you need to fill it.

There are a few calculations used to determine how much material you need. First, you need to find the volume of the mold box in cubic inches. Most molds are square or rectangular in shape, so we use the simple math formula length x width x height to determine the volume.

• Formula: L x W x H = volume (cubic inches)

Ex.) Box dimensions: 11 ½ inches x 5 ¾ inches x 2 inches = 132.25 cubic inches (in3)

Once you find your mold box volume, you also have a model(s) inside that will take up space. This will reduce the amount of material you need to fill the space. You can calculate the volume of your model(s) using the same formula.

Ex.) Stone dimensions: 9 ½ inches x 3 ¾ inches x 1 inch = 35.625 in3

If you’re using multiple models, you’ll need to determine the volume of each. You can then add each model volume together to get an overall total model volume.

Once you have both volumes for your mold box and model(s), you’ll need to subtract them from each other to figure out how much of the space needs to be filled.

• Formula: Box volume (cubic inches) – model volume (cubic inches) = total volume of material needed (cubic inches)

Ex.) 132.25 in3 – 35.625 in3 = 96.625 in3

The next thing you’ll need to do is convert your volume into a weight measurement, like pounds (lb). The information you’ll need to do this is specific volume. VFI provides this property for all our products under liquid properties on each product page and technical data sheet. We typically recommend using 26 in3/lb. because it will accommodate some extra material in the event that waste occurs.

You’ll need to divide the cubic volume by the specific volume to determine the total weight of material needed, which means the combination of both A and B side materials.

• Formula: cubic volume ÷ specific volume = weight (pounds)

Ex.) 96.625 in3 ÷ 26 in3 = 3.7 lb. (Part A + Part B)

We would then round that number to a whole number (4 pounds). You would then look at mixed liquid density, also known as weight per gallon, to determine how much material to order. Most of VFI’s rubbers, with the A and B sides combined, are 8-9 pounds per gallon. Because VFI’s rubbers come in 1-gallon kits, 5-gallon kits, drums, or totes, we’d recommend a 1-gallon kit of material for this specific project.

Note: Many people have poured water into their mold box to determine how much material they need. However, this can be risky because urethane is sensitive to moisture. Getting your mold box and models wet can cause adhesion, curing, and bubbling issues. Some models will be very porous, so ensuring they are dry and sealed properly before pouring the rubber is essential.

Accounting for Waste

Material can be lost through accidental spills or as it clings to the sides of mixing containers and mixing equipment. Since waste occurs, it is recommended to add 5-10% more material to your estimate.

In most cases, having more material saves time and money when accounting for this waste. If you don’t have enough material, it might disrupt the mold-making process and create more waste than anticipated.

Contact VFI if you need further assistance determining how much rubber you need to make your molds.

Qwik Spray vs High Pressure Spray for Hard Coat: Which to Use?

The two most common spray methods VFI hard coat products utilize are Qwik Spray and high pressure spray. Spraying, in general, provides applicators with several advantages – speed, uniformity, and reduced labor costs – compared to roller and brush applications.

Those new to spraying can benefit by starting with a cartridge-based applicator. However, it can also be hard to know if it is the best application method for you. There may come a time when your production line could benefit from upgrading to a high-pressure spray rig. Maybe you started making small displays and signs for retail stores but have recently been contracted for bigger work by theme park and attraction companies. VFI has excellent technical and customer service support to guide you when making this important decision.

Note: Always wear proper protective equipment (PPE), including an approved respirator, regardless of what equipment you’re using. Also, utilize a well-ventilated spray booth where necessary.

Qwik Spray Gun Requirements

VFI-6171 70 D Qwik Spray Hard Coat is the cartridge-based polyurethane formula VFI recommends for protecting smaller EPS theming elements. To use the material, you will need a VFI-7500 Qwik Spray Gun capable of holding 750 mL dual cartridges, an air compressor that supplies clean, dry air at a minimum of 100 psi and 10 cfm of constant pressure, and GS-15 Static Mix Tips.

VFI-6171 is stored in cartridges with two separate chambers for the A (Iso) and B side (Poly) materials. The design of the cartridges ensures a precise 1:1 mix ratio by volume that achieves a quality protective finish. Once the trigger is pulled, the components are pushed into and mixed through the static mix tip, which initiates a chemical reaction that cures the material after it exits the tip. The GS-15s have an 11-inch mix tip with a 3/8-inch inner diameter, which creates a fine texture on surfaces.

High Pressure Spray Rig Requirements

VFI-6170 70 D Spray Hard Coat is the high pressure polyurethane formula VFI recommends for protecting larger EPS theming elements. To use this material, you will need a two-component air, electric, or hydraulic sprayer that runs at a minimum of 150-155°F and 2,500 psi of constant pressure, with heated lines. Some spray rigs that accommodate these requirements are:

• Graco A-XP1 air sprayer
• Graco Reactor 2 E-XP2 electric sprayer
• Graco Reactor 2 H-XP2 hydraulic sprayer
• Graco Reactor 2 H-XP3 hydraulic sprayer
• PMC PHX-2 hydraulic sprayer
• PMC PHX-25 hydraulic sprayer

Advantages of Using the Qwik Spray Gun

1. Portability

A big reason the Qwik Spray System is so desirable to many users is because all you need is the lightweight applicator and enough cartridges to cover your piece at the desired thickness. Since this method is typically recommended for smaller projects (under 90 square feet), you’ll probably only need a kit of material, which is just 6 cartridges. With improved portability of the material and equipment, you can go from job to job much easier and aren’t held down to a single location for spraying. Note: This will also be dependent on the size of your air compressor.

2. Cost-effective for Small Projects

If you’re spraying small sculptures, custom signs, scenery, or props for a museum, retail store, theater production, etc., the VFI-6171 formula is preferable. Small projects typically include pieces 4 feet x 6 feet and under. Anything over this size will generate a large amount of overspray. Other small jobs this material can help with are if you need to repair an existing hard coat that has become damaged or adhere large EPS pieces together for a larger project.

The Qwik Spray Gun is more affordable, and while the material might cost more, you’ll save a lot on equipment if you’re not hard-coating massive theming projects. If you want a quality spray rig, they can cost upwards of $20,000-$80,000 or more. The higher end would be for mobile rigs with compressors and generators, so your spray equipment is easier to transport.

3. Better for Minimal Spraying

Many applicators can’t justify the price that comes with high pressure machinery if they are not spraying frequently. The Qwik Spray System is a great alternative if your production only calls for spraying a couple of times per month. However, there are situations where applicators have justified upgrading even if they only spray once a month.

Someone might eventually switch to high pressure if their spray load increases substantially, as they would save upwards of 60% in material costs if they switched from Qwik Spray. Two cartridges are just under a gallon of material and are significantly more expensive than purchasing in gallons or drums.

4. Limited Training Necessary

Another reason users desire the cartridge-based applicator is due to ease of use. Because the machinery is less advanced, applicators don’t need as much training to use it. If you’re new to the Qwik Spray System, check out our how-to-use guide with pictures for easy assembly and tips on spraying.

VFI recommends this spray applicator to get users started when they don’t have any previous experience. It allows applicators who are used to applying coatings with brushes or rollers to experience a low pressure version of spraying. Note: If you’ve never sprayed before, it will take some practice to achieve a consistent, desirable finish.

5. Low Maintenance

A big perk about cartridge-based spray application is that there are no spray lines to clean after spraying. Empty cartridges and static mix tips can be thrown away after use, so there’s limited mess and maintenance. The cartridge-based applicator does not require frequent use to keep it in working condition.

On the other hand, high pressure spray equipment requires a lot of maintenance to prevent downtime from chemical buildup, corrosion, and other factors. You have to clean spray nozzles, pumps, lines, etc. frequently. VFI offers VFI-8005 Pump Flush for cleaning spray lines to prevent material from clogging the equipment. It also has more parts that can wear over time, so it’s important to inspect and replace them to ensure your equipment is in working order.

Advantages of Using a High-Pressure Spray Rig

1. Better for Increased Project Volume

If you’re suddenly spraying almost every day vs a couple of times per month, it may be time to upgrade to a high pressure spray rig. As mentioned, the material costs for a cartridge-based system are more substantial. When you start to notice that you’re buying cases upon cases of cartridges, switching over to drums or totes can make a huge difference.

Note: High pressure spray rigs must be used often to keep them in working condition. If you do not have plans to use the spray rig, you should flush the spray lines so that coating residue is not left to solidify or crystallize.

2. Better for Versatile Spraying

When you have a high pressure spray rig, there’s no limit to the types of jobs you can work on. Whether your carved EPS structure is small, medium, or large, the spray rig will accommodate it.

Another thing that makes high pressure rigs so versatile is that they can be used with different materials. Polyurethane and some hybrids are typically the only material that can be used with cartridge-based equipment. If you’re looking for a material that’s a bit softer than a polyurethane or hybrid coating for your theming project, high pressure polyureas have been used in their place.

3. Better for Fixed Location Spraying

While the portability of the Qwik Spray Gun is desirable, if you’re not going on-site to spray a hard coat, that portability doesn’t always matter. Many theming designers have workshops where they do it all: carve shapes and forms, spray hard coats, and paint over them. These shops typically also have a designated spray booth to contain overspray and protect their work environment and workers from harmful spray fumes.

4. More Control While Spraying

A negative part of the application process when using a Qwik Spray Gun is once you start spraying, you’re not supposed to stop. Continuous spraying is necessary because if the flow is stopped, the coating will clog up in the static mix tip. You need to plan your spray route ahead of time for a consistent, uniform finish. If you want to stop, you’ll have to switch applicator tips before you start again.

With a high pressure spray rig, you can start and stop when you need to. Having control also reduces the amount of material used, so there’s less waste.

5. Improved Cured Surface

Something that tends to be insignificant to some applicators but can save on time and labor costs is how the coatings cure. The high pressure hard coat formula comes out smooth, seamless, and free of blemishes due to the pressure and speed at which the coating exits the applicator. It has less time to interact with the environment, which could cause potential issues.

The Qwik Spray formula, on the other hand, is slower and doesn’t come out of the applicator with as much force. This gives it more time to interact with the environment, which creates a foaming effect from moisture in the air. While the surface irregularities aren’t that noticeable, it will be more textured. This might create more post-work, such as sanding before the application of a top coat can occur.

Contact VFI if you’re still trying to determine whether the Qwik Spray or high pressure hard coat is better for your unique project.

How to Use a Brushable Hard Coat + Testing for Recoat Window

Knowing how to use a brushable hard coat can save you money on labor costs and material waste. Before you begin working with new materials, always read the labels on the supplied containers. If it is difficult for you to read the labels, VFI offers technical data sheets with thorough instructions on every product page under resources.

If you’ve never worked with a brushable hard coat, you can also check out our detailed how-to video here.

Through this article, we will provide various tips for using one of these products. An important aspect of using a brushable hard coat is adhering to the recoat window. So, we also wanted to show you how we test for that.

Preparing Your Foam for Hard Coating

Typically, users apply these coatings to EPS foam. We recommend 2 PCF foam for the best cost-to-quality ratio. Allow the foam to age for 30 days minimum before coating it.

After carving the foam, it must be free of particles that might disrupt adhesion. Clean off the piece with a vacuum or compressed air. Also make sure the piece isn’t damp as this could also affect adhesion.

PPE for Applying Brushable Hard Coats

VFI recommends using personal protective equipment, including gloves, long sleeves, and safety glasses, when working with these materials. Please see the material SDS for more information.

Even though the coating is not sprayed, a respirator is required when sanding. Inhaling or ingesting these materials as particles can be toxic.

If you have a spray booth, it’s a good idea to work inside it while sanding. The fans will help keep the sanded hard coat particles inside the booth and away from your facilities.

Preparing Your Workspace

First off, these materials are sensitive to moisture. It is highly recommended that you work in a temperature-controlled environment around 72°F with low humidity.

If you don’t, bubbles will accumulate during mixing and application. These bubbles will then cure on and in the finished surface. The entire piece will require sanding and a new coat, depending on your desired finish.

Measuring the Materials

These are two component materials with a mix ratio of 1A:3B by volume. Since the B side is thicker and more of it is needed, we recommend measuring that material first. It’s much easier to pour the A side into the B side when ready.

We also recommend measuring how much of each material you need by weight rather than by volume. To do this, you will need an accurate gram scale. It helps you avoid making errors that could occur when measuring by volume.

Another tip when using these coating materials is to never use a full kit of material. Doing so will shorten the working time, which includes the time it takes to mix and apply it.

• VFI-2519 75 D Brushable Hard Coat has a mix ratio of 1A:3.44B by weight. To make calculations easier, we recommend using 100 grams of A side to 344 grams of B side. For an even smaller amount, use 50 grams of A side to 170 grams of B side.
• VFI-2626 65 D Brushable Hard Coat has a mix ratio of 1A:3.55B by weight. To make calculations easier, we recommend using 100 grams of A side with 355 grams of B side. For an even smaller amount, use 50 grams of A side to 175 grams of B side.

Note: when you’ve set aside the material you will be using, nitrogen purge both containers before closing them to extend the life of the unused material. You can find nitrogen purge kits on Amazon if you don’t have one readily available.

Mixing the Components

The second the materials touch, a reaction occurs, and the pot life begins. You’ll want to mix them using the double-bucket mix method. We recommend using a 1-gallon paint stir stick. You can find them at any home improvement store. Make sure to scrape the sides and bottom of the mixing container. Once you are done mixing in one container, pour the material into a new, clean mixing container and mix again.

It’s somewhat easy to tell when you’re done mixing because of how different the materials look. The Iso (A side) is very dark, and the Poly (B side) is very light. When the combined material is a uniform, neutral color, you’ve probably mixed it thoroughly and can begin applying it. You don’t want streaks of either material in the mix; otherwise, areas in the coating will be tacky and may never cure.

Applying the Brushable Hard Coat

When applying the material, use a non-shedding chip or foam brush. You can use a roller if you desire, but it must be a sponge roller, not a nap roller.

If you’re applying it to non-horizontal surfaces, you’ll want to wait a few minutes for the material to thicken so it doesn’t drip. If the coating does sag, you must sand it for a smooth finish.

Apply at least 60 mils to ensure a uniform film. Use a mil gauge to test the thickness of the layer.

If you plan to apply additional coats, you must stay within the recoat window. VFI-2519 has a recoat window of 4 hours at 50 mils. If you apply it at a greater millage, it may affect the recoat window. If you miss the recoat window, you must sand the coating before applying another layer.

Setting up to Test VFI-2519 for Recoat Window

While on the topic of recoat windows, we wanted to explain how we would test for this property. The test method is arbitrary, so there is no industry standard.

A recoat window is the time after an initial coating has been applied that a secondary coating can then be applied, ensuring a strong bond between the two layers.

For the test, we mixed up small batches of the VFI-2519. To ensure we had a sufficient amount of material, we used 206 grams of Poly (B side) and 60 grams of Iso (A side) by weight.

We applied the coating to a pre-sanded board of VFI-2538 70 D EPS Form Hard Coat, which is a similar urethane hard coat. We spread the brushable coating onto the board at 50 mils thick with a square film applicator.

The temperature was 75°F with a relative humidity of 70%. Because the humidity was so high, we immediately noticed bubbling in the mixing cup and the coating as it started to cure on the surface. This wouldn’t affect what we were testing for, but it is something to avoid if you want a smooth, bubble-free finish.

We didn’t think we would get good results if we tested the material in half-hour intervals at the start, so we applied a second 50 mil coat after the first had cured for 1 hour and 2 hours. These second coats were applied at 79°F with a relative humidity of 66%.

We also coated a second board to test in half-hour intervals from 2.5 to 4 hours. The first coats were again applied at 50 mils with the square film applicator. The temperature was around 71°F with a relative humidity of 70%. With the humidity still around the same as the first board, we noticed bubbling in the coating again.

We then applied another 50 mils on top of the first coat after it had been curing for 2.5 hours, 3 hours, 3.5 hours, and 4 hours. Note: A 5-hour test was also tacked on since we had room on the board.

The temperature was between 70-71°F with a relative humidity between 70-76%. The new layers also started to bubble. Increased bubble formation may have occurred because the previous coating was still off-gassing as well.

Testing Adhesion for Hard Coat Recoat Window

We left the boards to cure for the rest of the day before we could prepare them to test their intercoat adhesion for the recoat window.

The surface was sanded before we applied dollies from the Elcometer 106 Pull-Off Adhesion Tester to each test section with an epoxy adhesive. We left the adhesive to cure for 3 days to ensure the dollies were firmly attached to our testing surfaces.

With the dolly cutter (bimetal hole saw), we cut around the base of the dolly so lateral bonding wouldn’t interfere with the test. We then removed the excess coating and adhesive shavings.

The base support ring was placed over the dolly to ensure a flat surface. The tester claw was then clamped onto the dolly, and the wheel on top of the tester was tightened to apply a perpendicular force that would pull the dolly off. The indicator on the tester retains a PSI value at which the coating separates from the surface.

Results of the Recoat Test

We wanted to see two things from the pull-off test:

• An acceptable PSI for tensile strength
• The two coatings still adhered together

If we only saw one layer of coating and/or a low PSI, that would be a failure.

The 3.5-, 4-, and 5-hour samples failed at 200 PSI, while the 2.5- and 3-hour samples failed at 400 PSI. The 2.5- and 3-hour samples maintained intercoat adhesion, which was a success. While the 5-hour sample failed at 200 PSI, it maintained intercoat adhesion.

That’s how we determined that a second coating could be applied at 50 mils up to 4 hours after the first. We also determined that reapplication 1-2 hours after applying the first coat is not recommended. The recoat window can always change depending on the film thickness, application surface, and temperature.

Applying VFI-2519 after 4 hours will compromise the adhesion between coats. After this time, the initial coat would have to be sanded and/or primed before another could be applied.

Contact VFI if you need more assistance when applying multiple coats of a brushable hard coat.

Why Is My Hard Coat Cracking?

Hard coats are supposed to be durable protection over surfaces like EPS foam for theming, so why are customers experiencing cracking? Cracking is a stress-related failure, which stems from substrate movement, lack of flexibility, extreme temperatures, and improper application.

Reasons Hard Coats Crack

Reason #1: Substrate Issues

Using the incorrect substrate for a hard coat can cause future issues. A general rule of thumb is you cannot apply a rigid coating to a surface that is softer or more flexible than the coating.

Hard coats are high on the Shore hardness scale. VFI’s hard coats are 65-75 D, which makes them feel very plastic-like, similar to a hard hat. Since these coatings have higher hardness properties that limit their flexibility.

Certain surfaces are more flexible and will expand and contract in extreme environments. Because the coating is rigid, it won’t be able to bend and flex with a surface that is more flexible than itself. This lack of flexibility makes them more susceptible to cracking from substrate movement.

Reason #2: Environmental Factors

Your hard coat’s ability to handle stress is closely associated with the environment. If your theming project is exposed to extreme temperatures, sunlight, humidity, and impact, it will degrade eventually.

Hard coats traditionally do not handle thermocycling or weathering very well. Our hard coats have a heat deflection temperature of 107°F, which means they will start to distort under stress at that temperature. This is a reason they need to be supported by a surface. The good thing about using EPS foam underneath is that the coating will hold strong unless the foam fails.

However, if you are installing the project in a location like Las Vegas where temperatures are high year-round, expect cracking to occur over time on dark surfaces. While substrates like EPS foam have good thermal stability, once they reach above 170°F they will start to fail. The failure of the substrate is what causes the coating to also fail and crack.

Reason #3: Improper Application

Coatings can fail if they aren’t applied correctly. If the surface is dirty or contains contaminants before the coating is applied, it can affect adhesion. If the coating is not properly adhered to the surface, it can delaminate, peel, or crack.

Applying the coating outside the recommended thickness range can also cause issues. If the coating is applied too thick or too thin, it has a greater chance of cracking. It will be very brittle unless it reaches a certain thickness.

Solutions

No one wants their hard coat to crack. These failures lead to extra costs, material waste, and project delays. The best way to prevent cracks is to use the right coating system and substrate for your environment.

If temperatures get above 170°F, a hard coat over EPS foam is not the recommended material. For a hard-coated project to last as long as possible, it should be placed in a relatively temperature-stable environment.

There is an alternative to using a hard coat. You can use a softer, more flexible coating. Softer coatings provide the needed flexibility to accommodate stresses and impacts without affecting the underlying surface. You may also need to use a different substrate.

VFI offers several products that will work for various application needs. VFI-3119 70 A Polyurea Hybrid Spray Coating is a softer coating that can be applied to flexible surfaces like flexible foam. It offers great resistance to thermocycling and outstanding durability in diverse climates.

We’ve also seen theming fabricators use other substrates to create more durable structures. EPS foam is only going to get you so far with its thermal stability. If you created your structure from a material like metal or wood, it would have better thermal and structural stability.

VFI typically recommends a polyurea hybrid coating like our VFI-542 High Pressure Spray Bedliner for metal surfaces. It’s a cost-effective material in comparison to some polyurea and polyurethane coatings on the market. At 40-50 Shore D, our bedliners have more of a rubber-like feeling. They also have the ability to withstand cracking, warping, and peeling in extreme hot and cold temperatures.

A few other tips to remember to prevent cracking include:

• Ensuring proper surface preparation and application of your coating.
• Following the manufacturer’s instructions listed on the technical data sheet.
• Remember that if you apply paint as a topcoat, it has to be more flexible than the coating beneath it, otherwise it will crack.

Contact VFI if you need assistance finding the right hard coat material for your specific theming project. We also have recommendations for what you should and should not use to repair hard coat cracks.

How to Fix Holes or Cracks in Urethane Hard Coat?

Accidents can happen when using urethane hard coats over EPS foam shapes, signs, and props. We’ve had customers call in about cracks, holes, and dents on their sprayed hard coat layer and are looking for a fix. While we’ve heard of many DIY options, such as Bondo, plaster, and other polyester resins, the best repair material is a brushable urethane hard coat.

What Is the Problem with Other Repair Materials?

The biggest reason you shouldn’t use other materials to repair a hard coat is because they won’t be as compatible. A brushable material like VFI-2519 75 D Brushable Hard Coat has similar capabilities as a sprayable material like VFI-6170 70 D Spray Hard Coat.

At their core, these coatings are both polyurethanes. When properly prepared, a new coat of urethane bonds extremely well to a previous coat. The brushable hard coat can create an effective seal on the old hard coat, so the repair appears seamless. The ability to sand and paint the hard coats is comparable as well, so it’s easy to blend the repair in with the rest of the coating.

Patching materials like Bondo or plaster won’t be able to behave exactly like a hard coat. Bondo is commonly used for autobody, boat, and home repairs on surfaces like wood, metal, concrete, and more. Plaster is typically used as a building material or to patch cracks and small holes in walls and ceilings. These materials may not adhere well to polyurethane coatings.

Another reason to use a brushable urethane hard coat is that it will be able to match the properties of the existing coating. At around the same hardnesses (70 D vs 75 D), they offer similar abrasion, impact, and wear resistance. While they are formulated to be rigid, they also have good flexibility to prevent cracking. They offer these benefits whether you apply them by spray or by brush.

While Bondo and plaster are very rigid after they have cured, they won’t allow for the same amount of movement. If the hard-coated foam surface moves when temperatures are elevated, the repair material will move with it. Eventually, the Bondo or plaster repair will crack or fail over time, which defeats the purpose of using it as a repair. Also, polyester can melt the foam underneath, which is more trouble than it is worth.

Because the hard coat is meant to be painted, Bondo will cause issues with the topcoat. When paint is applied to the polyester resin, it will off-gas and wreck your paint. If these repairs are large, your overall piece might not look good.

Ultimately, these materials are too dissimilar to the original polyurethane hard coat to stay bonded together and undamaged. A urethane-based material will offer better adhesion, durability, and flexibility for repairs.

Solution

So, while you can use Bondo or other materials to repair cracks and holes in your coating, it’s better to use a brush-applied hard coat repair like VFI-2519 or VFI-2626. VFI-2626 has fire retardant in its formula, so it’s the better choice for indoor projects.

How to Use the Repair

When repairing an existing hard coat, you will need to remove any broken-off pieces in or around the damaged area. You will also have to sand in and around the damaged area to ensure adhesion of the repair material to the previous coating. Once the damaged area is prepared, mix up your repair material by weight or volume.

Before using the repair material, it is best to let it sit in the cup and heat up a bit so it gets thicker. This will make it easier to fill the hole or crack. An alternative to this method is to add fumed silica to your mix. This addition will make your mix very thick, like a paste, so it fills holes or cracks even better.

Fill the crack or hole until it is level with the rest of the hard-coated surface. We recommend using a rubber scraper to smooth and remove excess material when it’s still in a tacky state. Allow the patch to cure before sanding or painting it for theming purposes.

Contact VFI if you need assistance using a brushable hard coat repair or if you have any other questions.

Why Is My Hard Coat Project Failing?

In the past, we’ve had customers think they could use a hard coat in a casting capacity for theming projects. They spray the hard coat into a mold and demold it once cured to create a lightweight part without adding support beneath it. The most likely explanation for why the coating is failing is that it was left in high temperatures without support.

Reasons Unsupported Hard Coats Fail

By definition, coatings are materials designed to create a layer over or cover the surface of an object or substrate. Hard coats are best at creating durable, protective films over EPS foam. They are not made to be a casting material or to create hollow shapes to save money.

You might think that since hard coats are hard and durable, they can create three-dimensional shapes without a supportive surface underneath. However, they lack the structural rigidity and strength to support themselves. Without a support structure, they are thin, slightly flexible, and won’t last long due to various conditions.

An unsupported hard coat will eventually weaken and deform when exposed to high temperatures and UV rays. This can lead to a ruined project or noticeable imperfections in the piece. A support structure can help the coating maintain its dimensional stability, preventing warping, cracking, and distortion.

Outdoor temperatures can surpass the coating’s heat deflection temperature (HDT). HDT is a property that measures a material’s resistance to distortion under a given load at an elevated temperature. In other words, it will tell you how well your coating can handle a high-heat environment before it will deform.

Hard coats with a lower HDT than the environment they are being installed in will need to be fully supported. An example of this would be if you were to use an EPS hard coat in an outside environment. The hard coat gets structure from the EPS at high temperatures. If you are installing your project in a location where temperatures get above the HDT and you are not supporting it, that hard coat is not recommended.

Depending on what it is used for, a hard coat can also deform from impacts. They’re sprayed thin (up to 120 mils or a 1/4 of an inch), so they can be susceptible to cracking under impact. A support layer will absorb some energy from the impact, reducing the risk of damage to the hard coat.

Solutions

Polyurethane is a versatile material that can accommodate a variety of applications. Its properties can be adjusted to make it hard or soft. Depending on the raw materials used, it can be made into a foam, coating, rubber, or plastic. Hard coats have a similar feeling to plastic, which is why they may be useful in some casting scenarios.

• The first solution to prevent your hard coat from deforming is to spray over a surface that will support the coating. These coatings are typically sprayed over EPS foam to harden it. They create a durable, weather-resistant finish without diminishing the details of the underlying structure. EPS foam has good heat and thermal stability, so the hard coat shouldn’t fail unless the foam fails. Using foam also doesn’t add too much weight to the piece. Plus, it is cost-effective, so it won’t increase the price too much, either.
• Another solution is to spray the urethane coating into a mold, treating it like a fast-setting plastic. It must be backfilled with expanding foam once it has cured. A material like urethane foam is lightweight like EPS and will provide the support the hard coat needs. There is a range of urethane foam options with varying densities to accommodate your specific project.
• Rather than use a hard coat, you could use a urethane plastic with a high heat deflection. These high-performance plastics are good for high-impact applications and can be exposed to environmental temperatures up to 205°F (96.1°C) without deforming. The only downside is that you’d need more material to make these castings, so they will cost more.
• One last option would be to use a urethane plastic capable of being rotocast and then backfill it with expanding foam for support. Using this material will depend on your intended application. Not all plastics have high heat deflection temperatures, so you’ll want to be aware of that, too.

Contact VFI for more information on our urethane sprayable plastic coatings and plastics.

Why Isn’t My Urethane Hard Coat Drying?

Customers of urethane hard coats have called VFI asking why their urethane hard coat isn’t drying. Mix ratio, poor mixing, application thickness, and temperature can all cause urethane to not dry.

Urethane coatings can sometimes be hard to work with if you’re new to the material. Read the material technical data sheet (TDS) before you begin working to avoid errors.

Reasons Urethane Hard Coats Might Not Dry

Issue #1: A hard coat customer reached out about the coating not drying correctly over EPS foam. After talking through his issues, we discovered the problem. He was trying to use the hard coat more like paint. He sprayed in several thin passes at less than 20 mils per pass.

For a urethane hard coat to dry properly, a minimum amount must be applied to the surface. When applying to EPS foam, it must be sprayed thicker, or it won’t fill the foam in and will have a popcorn-like finish.

Issue #2: Another issue we’ve seen urethane hard coat users run into is using the wrong mix ratio. This is typically not an issue for those using spray rigs with proportioners. It is more likely for brushable hard coat users.

If you’re measuring the material by volume, you can mistakenly read the lines on your measuring cup wrong. Using too much of one material or not enough of another can result in your hard coat not drying.

Issue #3: You may notice the coating has some sticky spots after allowing it to dry for a few hours. The tackiness is unmixed material. Failure to thoroughly mix the material creates these spots.

Again, this is typically a problem for brush-applied coatings. However, off-ratio spots can happen in sprayed coatings if the proportioner becomes off-ratio at any point. When using cartridges, the mix may be off-ratio at the beginning or end of the tube as well.

Poor mixing can occur because users are worried about the working time and are in a rush. If you are using large amounts at once, your working time is reduced, which can also cause mixing errors.

Issue #4: Another factor that controls the drying time of a hard coat is temperature. This means temperature of the environment, application surface, and material. If you work in cold conditions, it can take your coating much longer to dry. In freezing conditions, the hard coat may never dry correctly.

Solutions

If your coating isn’t drying, you may have to start over or do large-scale patches. Follow the manufacturer’s instructions on the technical data sheet. Surface preparation, mixing, application, and drying instructions should all be included.

Work in a temperature-controlled (77°F) location. Warming up your material to at least 65°F can help it perform to standards. Avoid storing or applying in very cold or hot conditions for optimal results.

When weighing out your material, VFI recommends using the mix ratio by weight instead of volume. It’s easier to notice if you go above or below the amount of the material needed on an accurate scale.

Mix up your material in smaller amounts. This will help you avoid poor mixing by extending the working time of the material. Mix the material in one container until it is a uniform color. Scrape the sides and bottom of the container while mixing. Pour it into a new, clean container and mix again to ensure all parts are sufficiently mixed.

If you are using hard coat cartridges, make sure to spray on a disposable surface before spraying onto your piece to ensure no off-ratio material is used. When your cartridge is almost empty, spray onto the disposable surface again.

VFI recommends applying urethane spray hard coats at a minimum of 40 mil passes to create a uniform film that protects the piece. The minimum application rate for a brush-applied hard coat is a little higher at 60 mils. Depending on the application, you may want to increase the thickness for better impact resistance.

Increasing the temperature after application can help the material cure faster. Make sure the relative humidity is low so the coating doesn’t bubble.

Contact VFI if you have more questions about troubleshooting hard coat issues.

Why Should You Hard Coat EPS Foam Props?

There are several reasons that you should hard coat EPS foam props. If they are being used or moved around frequently and are getting dinged, dropped, or even smashed in the process, they won’t last.

If these props are meant for outdoor use, they will wind up broken and damaged from weather conditions, including rain, sunlight, and extreme temperatures.

Even if your props aren’t meant for close human interaction, accidents can happen. If you plan to reuse your props or need them to last the entire production, they can’t be left unprotected.

A way around this has often been with fiberglass, but this material is expensive and time-intensive to use. An alternative is to harden your foam props and set pieces with a high-strength, protective EPS theming hard coat.

What Is EPS Foam?

EPS foam is often called styrofoam by many prop designers, but they are not the same. Styrofoam is a brand name for extruded polystyrene (XPS), whereas EPS is expanded polystyrene. While they use the same polystyrene base, the manufacturing process for each type is different.

Other foams can be used for props and set pieces, but EPS tends to be the easiest to work with, making it the most desirable. Compared to other materials like wood, metal, or concrete, it is also more affordable. It can be purchased in blocks or sheets at varying densities if it needs to be tougher for the desired project.

It is most recommended for props if they are to be moved around, which is frequently needed for movie, television, and theater productions. The lightweight nature of the foam makes it the obvious choice for creating large, oversized props. It allows productions to be more dynamic and efficient for smoother movement and transitions between scenes.

How Do You Make EPS Foam Props?

These days, most of what we see on our screens in terms of movie props and sets is computer generated. CGI took the industry by storm, but audiences are reverting to the desire for authenticity in media. Physical sets and props can bring back that authenticity. Making physical props is more affordable and easily customizable when you hard coat EPS foam. The prop making process goes like this:

• Designers and prop artists typically start by creating and mapping out a design using a computer program. They can be as creative as they want, which is helpful for designing realistic or imaginative props and set pieces.
• Following the creation of the prop design, foam is then carved using a number of methods, including CNCing, milling, hot wire cutting, etc. Shaping the foam is the most delicate part of the prop making process because of how fragile the foam can be, especially when adding extreme detail.
• Once you’ve gotten through the hard work of carving or machining the foam, a hard coat should be sprayed or brushed onto the surface. As a coating, the material adapts to the contours, curves, and edges of the foam without diminishing the details.
• After the hard coat has cured, the surface is sanded to a smooth finish to accept paint or a topcoat. Painting is the part of the prop making process that allows designers to enhance the aesthetic appeal of the prop to look real and life-like. It can even make the prop look like other materials, including wood, metal, and stone. Even with a lower budget, prop masters can make high-quality props with foam and hard coats.

Best Hard Coating Material for Foam Props

While there are several ways to harden EPS foam props, VFI has seen the most success with polyurethane hard coats. At 65-75 D Shore Hardness, these coatings create a strong, seamless shell over foam props. Hard coatings come with many benefits, including:

• Fast cure – Other hard coating materials for foam props can take much longer to apply and dry. For example, fiberglass is durable, but epoxy or polyester resin has to be applied by hand. The resin then dries slowly, so projects take time to finish. Urethane sprayable plastic coatings are applied quickly and cure after a few hours, which makes them better for quick project turnarounds.
• High durability – Foam can be pretty fragile on its own. When hard-coated, it’s shielded to resist scratches, dents, chipping, etc., from movement or actors interacting with the prop. The coatings are also flexible enough to not crack from environmental extremes. They can be formulated with varying physical properties for long-term protection of the prop.
• Versatility – Urethane hard coats are versatile in many ways. They can be applied to large and small props made of various materials, including other foams like XPS and polyurethane. They can also be applied in different ways for different application needs. VFI specifically offers brushable, high pressure, and Qwik Spray hard coatings. These coatings can be used for indoor or outdoor projects as well, depending on if they have fire testing.
• Fire testing – Because many props and set pieces are used indoors, they may need to adhere to strict fire safety regulations. VFI’s urethane hard coats can pass ASTM E84 Class A fire testing. Class A is the highest classification these coatings can achieve under this test. In the event of an accident, the coating will not add to flame spread and can minimize damage.

What Kind of EPS Foam Props Can You Hard Coat?

Handheld props are often the most common props made of EPS foam. Since they are small and can be held, a brushable hard coat is typically the preferred coating to protect them. The only issue is that you must work in an environment with low humidity when applying brushable urethane to prevent bubbling.

If you are only making handheld props, the cost of a high pressure spray rig may be out of the question. Otherwise, if you’re making small props frequently, you might want a hard coat that can be sprayed through a cartridge-based gun.

On the other hand, the best way to hard coat oversized props and large set pieces is with a high pressure spray coating. If your set needs a rocky landscape, sculptures, or furniture, a brushable hard coat will not be able to accommodate the size of the piece. It’s also more cost-effective for a company that creates a lot of large foam props to get a high pressure spray system or a Qwik Spray Gun.

Hard coats can even adhere large foam pieces together, so brushable and spray applied coatings can be used in conjunction. Even if you are mostly spraying, it can be a good idea to keep some brushable hard coat around in case you need to make repairs.

Other props that designers may not realize could also be made of hard coated foam are architectural accents and custom signs. Foam makes an excellent alternative to stone and wood when making these features. We’ve even seen success with foam columns, trim, molding, shutters, corbels, signs, and more on the outside of actual homes. If these materials are used for decorative architecture, you know they’ll be able to withstand various conditions on movie and theater sets.

Contact VFI if you’d like to learn more about our hard coatings or need help determining the best one for you.

Why Is My Urethane Hard Coat Bubbling?

Customers of polyurethane coatings have called VFI about bubbles forming while mixing their material or when the material is curing. Bubbles can form for a handful of reasons, but when it comes to urethane, it’s usually due to moisture.

Urethane is a two-component material, and its A side (Iso) is very sensitive to moisture or water. Wherever there’s moisture in the environment, it will react with the coating and form carbon dioxide gas, which causes foaming or bubbling.

Reasons Bubbles Form in Urethane Coatings

Bubbles can occur regardless of your application method (high-pressure spray, Qwik Spray, or brush-applied). Some methods with a longer application time will be more sensitive than those with a shorter gel time. In most cases, bubbles are usually small and not always visible. However, it is best to avoid the following:

1. Humidity

Sprayable coatings don’t have much time to react with moisture in the air, but if the humidity is relatively high, you might experience bubbling. This is also true if you apply the coating while temperatures are fluctuating.

Brushable coatings like some urethane hard coats are a slowed-down version of a typical sprayable urethane. Their longer pot life and cure time allow for more moisture absorption to occur during the mixing, application, and curing process. When you start mixing the components in a humid environment, bubbles will form and continue to form as the material is applied and left to cure.

Spray coatings formulated to be sprayed through cartridge guns can also experience moisture issues. The material reacts slower and comes out at a lower pressure, so it can’t avoid a moisture reaction.

Products like VFI-6171 70 D Qwik Spray Hard Coat and VFI-2538 QS 70 D EPS Form Hard Coat are known to create a finish that is lighter in color and with more of a surface profile. That texture is a result of the material foaming as it interacts with moisture, even at a lower humidity.

2. Wet or Porous Surface

If you put a non-breathable coating over a wet or porous surface, any moisture underneath will be trapped. Hot temperatures can cause the surface to expand and increase pressure, and the coating will form bubbles or blisters.

Allow the surface to dry before application. If you’re working with a porous surface, you may need to seal it with a primer. For example, wood surfaces should be dry and contain less than 11% moisture; otherwise, they should be primed or mist-coated.

However, the coating may bubble if the foam isn’t allowed to age for 30 days after it has been manufactured. By coating the foam too early, you might seal gases within it, which could cause it to bubble as it cures.

3. Wet Application Equipment

For spray coatings, be cautious about water getting trapped in the spray hoses. A moisture reaction could occur if water gets in from humid or cold weather. The A side will react with the water and cause it to cure in the line. The B side will take in the water causing a foam interaction when sprayed. When the mixed material comes out of the gun, you’ll notice bubbling defects in the finish.

If the formula allows it, some applicators use chip or foam paint brushes to apply hard coats. Make sure that the application equipment doesn’t absorb moisture from the environment.

Solutions

Work in temperature-controlled conditions with low relative humidity. We recommend applying the material around 72°F. Cold weather can slow the coating’s cure, which could allow more bubbles to appear in the finish.

Avoid using hard coatings over wet or damp substrates. Make sure your surface is dry and prepared. Porous surfaces like wood might need to be primed. If you apply it over wood, it should contain less than 11% moisture. If you’re working with foam, allow it to sit for 30 days for any gas to escape.

If you’re spraying, ensure your lines are clear of moisture contamination. They should be cleaned after each use with a compatible pump flush or lube like VFI-8005 or VFI-8011. For brush applications, it’s best to use non-shedding chip brushes to avoid moisture absorption that could occur in foam ones.

If the coating is hard enough, bubbles can be sanded to achieve a smooth, uniform finish. Work with 120-grit or finer sandpaper to scuff-sand the bubbles. You’ll want to apply another coat to cover those defects after sanding.

Contact VFI if you need other technical assistance with urethane coatings.

Differences Between Silicone, Latex, and Urethane Molding Rubber

Learning the differences between silicone, latex, and urethane molding rubbers can help you determine which material is best for your next project. Regardless of the material you choose, they are all flexible and capable of producing highly detailed, durable molds. Their unique features can make one better for a certain application compared to another.

What Is Silicone Rubber?

Silicone is a synthetic rubber used to make brush-on or pour molds. It is a two-component material, and these parts are combined to cause a chemical reaction that converts the liquid into an elastomer.

Its main structure is composed of siloxane chains (silicon and oxygen). The manufacturer can adjust these chains to enhance the rubber’s properties for a desired project.

It is the most expensive rubber molding material. There are two common catalysts used to cure silicone:

Platinum-based

This type of silicone is also known as addition curing and uses a platinum catalyst. It’s a premium molding rubber that lasts longer than tin-based silicone but is also the most expensive.

This material can be formulated for various uses, including brush or pour application, skin-safe application, or food-safe projects when needed. Little shrinkage occurs when making molds, plus the material has great temperature stability and chemical resistance.

Tin-based

This type of silicone is also known as condensation curing and uses a tin catalyst. The tin catalyst makes it less expensive than platinum silicone.

It is used for general mold-making and prototyping, but it is not as long-lasting as other materials. As it ages, it will wear, lose elasticity, and become brittle.

Unlike platinum-based silicone, it is not prone to cure inhibition and can be used with most materials. It can create fine and intricate details for polyester, epoxy, gypsum, wax, concrete, and plaster casting. However, it is not suitable for skin application, even after curing.

It is prone to shrinking over time and as it cures. Its shrinkage partially comes from the release of methanol during the reaction. So, the bigger the mold, the less stable it will be. Fillers can make it more stable, but it will lose tear strength and become heavier.

Benefits of Silicone Rubber

• Its most appealing feature is that it does not require a release agent, so it demolds easily from most materials. It will also be able to withstand several casts without wearing significantly.
• Silicone can have varying properties, including Shore hardness, elasticity, working times, and curing times. This versatility makes it easier to choose one that meets your needs.
• Silicone is mostly formulated on the Shore A hardness scale. A lower hardness and ability to replicate details make them a great choice for historic restoration. There is a reduced chance of damage to the original or master.
• Regardless of where you need to make your molds, silicone works well for molding on or off-site. Various formulas offer fast cure times for easier in-field molding.
• It is not sensitive to moisture, so you can work in various conditions without worry of bubbles forming in your mold.
• It is desirable as a brush-grade material because it gets thicker better than urethane. Brushable formulas also replicate complex designs for specialty projects more easily. It is best for creating what’s known as a skin or glove mold. These molds will need wood or plaster backing.
• If you need your mold to withstand high temperatures, silicone works better in these environments.

Cons of Silicone Rubber

A downside to using silicone molds is that with repeated use, they will not last very long. Depending on the mold, they start to disintegrate or tear. They also lose their detail over time.

Because of cost, silicone molds are usually made with mold boxes or additional support, which will take added time and experience to develop.

These molds have poor abrasion resistance, so they’re not always recommended for casting concrete or materials like it. If you cast concrete, they work for low-volume production.

What Is Latex Rubber?

Latex is naturally sourced from rubber trees and was the first widely used rubber. It’s typically composed of rubber particles, water, proteins, and sugars, which all work together to provide a unique set of properties.

Compared to other molding rubbers, it is a thin material that can be brushed onto surfaces or sold as a sheet good. A brush-on mold can be desirable compared to solid molds as it saves on material costs.

Unlike other room-temperature vulcanizing rubbers, latex cures by evaporating the water and ammonia in its formula. Once cured, it leaves a highly elastic, durable mold that replicates perfect detail.

Benefits of Latex Rubber

• It’s the most affordable molding rubber and is extremely durable, so you benefit from a more cost-effective, long-lasting product.
• It has good strength, tear resistance, and flexibility, which all contribute to its longevity. It will last a long time in production if maintained and stored properly.
• In terms of ease of use, as a single-component material, it does not require measuring and mixing. Like silicone, little or no release agent is required to prepare the molding surface. It’s also water-based, so cleanup is easier and faster.
• Due to its abrasion resistance, it is good for casting abrasive materials like concrete and cement as well as wax and plaster. It is perfect for making flat molds for ornamental concrete projects like stone veneer and two-dimensional architecture. It can also be used for limited resin casting.
• Like silicone, it makes a good thin-walled glove mold but cannot be applied to the skin during or after application. By applying it with a brush, you can create molds with irregular shapes or very intricate molds with fine details.
• It is biodegradable, which makes it more environmentally friendly. This also means that, over time, when exposed to the elements, it can rot, degrade, and crumble.

Cons of Latex

Latex has a strong ammonia smell, which is undesirable during the extensive application process. When it’s not in use, it has to be stored at room temperature. If it freezes, it is unusable and must be disposed of.

While latex is strong, it has a high shrinkage rate as it cures. It can shrink as much as 10-20%, which causes it to lose fine details. It’s generally not recommended for casting urethane, polyester, or epoxy resins.

Because this material is used to make thin-walled glove molds, it requires rigid backing or a support mold. An unsupported latex mold will deform and stretch out of shape while casting.

Like silicone, certain materials can inhibit its cure like Vaseline and sulfur-based clay. Touching the surface of one latex layer before you add another can prevent it from curing. It’s also known to cause allergic reactions in some people upon skin contact.

Even though it is the cheapest molding rubber option, its multiple thin layer application method increases labor costs. Since only one layer can be applied at a time, and many coats are needed, it may take several days or weeks to make a single mold.

What Is Urethane Rubber?

Urethane rubber is another synthetic molding material for use in a variety of molding and casting applications. Like silicone, it is 2 part rubber that must be measured and mixed accurately. The chemical reaction occurs between an isocyanate and a poly. It is best for concrete casting.

Polyurethane is an affordable molding material. It is also more versatile because it can be formulated into different materials like plastics, foams, and coatings. It ranges between the A and D Shore hardness scale to accommodate various application needs.

Benefits of Urethane Rubber

• It has excellent physical properties that make it tougher than other molding materials. High properties include elongation and tensile strength for extended wear and tear, which are also customizable to meet specific performance requirements.
• Urethane is more dimensionally stable than silicone or latex, which means low shrinkage when making molds. It also maintains stability after substantial pressure is applied for consistent castings.
• It is more versatile than silicone or latex. Due to its range of property options, it’s used for a wide variety of projects. It can be formulated harder than other rubbers, which is better for tooling projects like stamps and formliners.
• Because it is highly durable, it can be reused over and over, especially in abrasive applications. Its reusability makes it the best material for high-volume production.
• Its ability to transfer pigment is better than other molds, which makes the color of the casting more vivid. It’s also more friendly to in-mold coatings and other modifications like painting. This ability is important to enhance the look of casting materials.
• Since urethane molds are thicker and solid, they typically don’t need rigid backing like silicone and latex glove molds. However, wood backing can be beneficial for large, flat molds to prevent shrinking in extreme temperatures.
• While release is required to prevent urethane from sticking to other surfaces, VFI offers a line of urethane rubbers that demold more easily. They have best-in-class release characteristics and are proven to lower breakage rates by 80%. This can be especially beneficial when demolding from delicate undercuts and details.

Cons of Urethane

The biggest downside of urethane rubber is that it requires a release agent before casting. It is highly adhesive and will bond to any surface. When making the mold, porous surfaces, including wood and natural stone, also have to be sealed properly.

Another downside of urethane is that it is moisture-sensitive in its liquid form. This can make it hard to work in warm and humid environments. If moisture finds its way into the mixture, it causes bubbles to form, which may affect your final mold surface.

Which Molding Rubber Should I Use?

What material you choose depends on several factors, including:

1. What is your budget?
2. What is your model or master made of?
3. What properties do you require? (i.e., high tear strength, high hardness)
4. What level of detail do you require? (i.e., extreme vs simple detail)
5. What material are you casting into the mold?
6. How many castings do you need to produce, or how long do you need your mold to last?

Molding Material Comparison Chart

VFI Coatings to Protect Flexible Surfaces

Volatile Free, Inc. has formed a niche line of softer coatings that provide certain applications with much-needed flexibility and strength. Almost 30 years ago, we started offering a diverse line of polyurea and hybrid coatings for the protection of various surfaces.

These coatings are versatile and used by industry experts across North America. Since they are softer, they have higher elongation, which means they have a better ability to stretch and flex. Due to this property, they withstand various conditions without breaking, protecting surfaces in the long term. On the other hand, they will have lower tensile strength.

The Versatility of a Flexible Polyurea Coating

Polyureas are desirable due to their adaptability and high properties. VFI’s two-component VFI-270 70 A Polyurea Spray Coating is no exception. It is a high-quality material with excellent abrasion and chemical resistance. Like most polyureas, this coating is fast-setting for high builds on vertical surfaces without sagging. The quick cure also allows for quick turnarounds on projects.

While polyurea can be used over a handful of surfaces, VFI-270 is best applied to flexible surfaces like a flexible foam. This is because the material itself is flexible and rubber-like at 72 Shore A hardness. The lower hardness also lends itself to resisting impacts better than harder coatings. Over foam, the coating creates an elastomeric surface without adding too much weight to the entire piece. Unlike other polyurea coatings, the film can be applied smoothly with no texture.

Typically, this material is used instead of other coatings due to its low moisture sensitivity. It can be used in various conditions, including high temperatures and high humidity. The only benefit it doesn’t provide is UV stability.

Uses: VFI-270 makes an incredible protective skin for foam parts and pads. This product has been used for artificial rocks, walls, and tree bark, amusement ride pads, spray-on cushioning, and to reinforce self-skinning foam. Depending on the thickness at which it is applied, you have control over what poundage of foam you back it with. It takes tint incredibly well, so you can color it to your desired aesthetic.

Polyurea Hybrid Flexible Coatings with High Properties

While polyureas are great, they don’t work for every situation. That’s where polyurea hybrids come in. Hybrids are a combination of polyurea and polyurethane, so they behave like a balance of both. Many of VFI’s flexible coatings are polyurea hybrids, including VFI-3119 70 A Polyurea Hybrid Spray Coating.

This coating works in a similar capacity to VFI-270. It is rather unique as a hybrid due to its higher tensile strength, tear strength, and elongation compared to the polyurea. It is rubber-like with a hardness of 70 A but it is incredibly tough and durable against impacts and cuts over soft or flexible surfaces. VFI-3119 is unique because it sprays like polyurea but wets out and flattens for a non-textured surface.

Like polyureas, it is fast enough to be applied vertically without dripping. Once applied, it sets quickly and provides a soft yet durable protective film. It has outstanding durability in diverse climates, whether used indoors or outdoors, with a UV-stable flexible top coat.

Uses: This coating can be used in high-impact applications with foam as the substrate. Surfaces requiring high rebound with good structural strength can also use this protective coating. It has been used as a wear and waterproof membrane and protective skin on furniture and seat cushions. Other potential applications include artificial tree bark, flexible brick panels, and faux animal skins.

VFI Flexible Coating Property Comparison

A coating’s properties strongly influence its performance in various applications. Because the coating may be subject to physical stressors over its lifespan, it needs a good balance of properties to withstand extensive damage. Below is a comparison of the mentioned coatings for more insight into their capabilities.

Benefits of Using a VFI Flexible Coating

Polyurea and polyurea hybrids can be formulated to achieve a range of properties. They are desirable for many reasons, including:

• Flexibility. The most special attribute of these coatings is their inherent flexibility, even at low temperatures. They will expand and contract with the surface due to temperature variations or vibrations, unlike thin, less flexible coatings. This ability allows them to flex, bend, and stretch without cracking, peeling, or delaminating from the surface for long-lasting protection. They accommodate movement without compromising their structural integrity.
• Durability. How durable a coating is will be one of the most important properties to consider when formulating it for protective purposes. These coatings should have the necessary properties to resist breaking, deforming, wearing, and tearing from high mechanical loads and stresses. These stressors can be caused by abrasion, impact, weather, and chemicals. Their toughness and strength ensure the longevity of the structure.
• Weather resistant. Humidity, low temperatures, and rain can degrade, crack, and discolor bare surfaces. These coatings are seamless once applied, creating a barrier to protect surfaces from substantial damage. The coating prevents water and other debris from passing through, reducing the likelihood of surface damage. Also, if moisture were to get through to the substrate, it could cause mold, mildew, and rot.
• Rapid cure. Because these coatings set up quickly, projects can be placed into service the same day. This is very desirable for applications that require quick turnaround times. Other materials, such as hand-applied polyurethane and epoxy, take much longer to cure, with epoxy taking days to be ready for service. VFI coatings dry within 4-6 hours and can withstand heavy-duty use within 24-48 hours, reducing downtime. The rapid cure also allows adequate coating thickness to be built in a single pass.

Contact VFI for more information on flexible industrial coatings. We can help you figure out the best material for your unique project.

Understanding the Properties of Industrial Polyurea and Hybrid Coatings

Understanding the properties of industrial polyurea and hybrid coatings is essential for proper use. Some industrial coatings enhance or protect surfaces, while others improve something as simple as aesthetics. Polyurea and hybrids are used almost solely for their protective purposes. VFI compiled information about the most important properties of these materials so you are better equipped to choose the right one for your project.

What Physical Properties Are Important?

When it comes to properties, there is a bit of a difference between polyurea and polyurea hybrids. Pure polyureas tend to have consistently higher physical properties than hybrids. However, both vary by formulation.

There are certain applications where polyurea is more desirable, such as environments where moisture is a concern. If moisture isn’t a concern, hybrids still have advantages and can be more cost-effective. The following physical properties are important to know regardless of coating type:

Shore Hardness

Test method: ASTM D2240

Definition: Shore hardness tests the resistance of a material to localized deformation or indentation. The material is tested using a durometer tool and is ranked on different scales between 0-100. Which scale is used is determined based on the material’s qualities.

Importance: Hardness is an adjustable property. Materials can come in different hardnesses to suit a customer’s needs. Industrial coatings will protect underlying surfaces when the correct hardness is chosen based on the specific application.

Polyurea or hybrid coating hardness is typically measured on the Shore A or Shore D scale between 40 A and 80 D. Materials on the A scale are typically softer, while materials on the D scale become much harder. For example, VFI-270 70 A Polyurea Spray Coating will be more flexible and rubber-like, while VFI-2622 68 D Polyurethane Spray Coating will be more firm and almost plastic-like.

A harder material is desirable for its resistance to scratches, dents, or gouges from abrasion. This is important in applications that experience daily wear and tear, such as truck bed liners, secondary containment, speaker boxes, table edging, and more. Lower hardness provides more flexibility and is desirable for applications like reinforcing foam for amusement ride padding due to higher impact resistance.

Polyurea and hybrids typically offer a good balance between hardness and flexibility to prevent cracking. They can bear weight or maintain their shape under various stresses. They will also resist punctures and penetrations.

Note: Most VFI products will have their Shore hardness in their name, specifying whether they are on the A or D scale, to make it easier to find what you’re looking for (ex. VFI-200 50 D Slow Polyurea Coating vs. VFI-3119 70 A Polyurea Hybrid Spray Coating).

Tensile Strength

Test method: ASTM D412

Definition: Tensile strength is a property that tests the maximum pull a material can withstand without tearing or breaking when being stretched. It is expressed in pounds per square inch (psi).

Importance: High tensile strength increases a coating’s ability to resist pulling forces, providing a higher tolerance to stress.

Good tensile strength is essential where surfaces experience impacts, expansion, contraction, or vibrations. In the instance of impacts, high tensile strength will help absorb the impact energy and prevent damage or deformation from occurring on the surface.

Like hardness, tensile strength also works with flexibility. A highly rigid coating could be prone to cracking, even with impressive tensile strength. That’s why polyurea and hybrids often offer a balance between all these properties to prevent failure. Certain hybrids might have a lower tensile strength, but this can be the trade-off for other desired properties like increased elongation.

Elongation

Test method: ASTM D412

Definition: Elongation is tested with tensile strength by stretching a material and measuring the increase in length it will achieve before breaking. It is expressed in a percentage (%) of the original length.

Importance: Industrial coatings can have high elongation, which is important for applications that encounter impact. Polyurea’s inherent flexibility is a factor that contributes to its ability to elongate and move with the surface without cracking or losing adhesion. They are formulated to be strong and flexible, which is dissimilar to other coatings that may break from movement or vibration. Elongation can also help absorb impacts, which is beneficial for applications like truck beds, recreational vehicles, trailers, or work trucks.

A higher elongation will mean a lower tensile strength, which makes it more elastic than rigid. If it is highly elastic and stretches easily, it might lack the hardness needed for certain applications. Polyurea offers a good balance of elongation with other properties to provide desired flexibility and durability. Hybrids might have lower elongation, but this can be made up with other higher properties.

Tear strength

Test method: ASTM D624 C

Definition: Tear strength tests the maximum force required to start a tear in a direction perpendicular to the stress. It is also known as tear resistance and is expressed in pounds per linear inch (pli).

Importance: Tear strength is another critical property for coating users. It tells you how well a coating will resist tearing and maintain its integrity as a protective barrier. High tear strength will prevent small punctures and abrasions from turning into large tears that could compromise the coating’s ability to protect the surface.

Even in an application with abrasive wear, the higher tear strength will prevent minor abrasions from turning into large tears that expose the underlying surface. In the event of impact damage, tear strength prevents the development of tears from a forceful blow.

Polyurea provides good tear strength and flexibility. Hybrids may have lower tear strength, but what they lack in one property, they can make up for in another one.

Water Absorption

Definition: Water absorption is the amount of water absorbed by a material. It is measured as a percentage (%) of the weight of water absorbed to the weight when dry. It can also be called moisture absorption or water swelling.

Importance: One of the most desirable uses for industrial coatings is waterproofing. They produce a seamless, impermeable barrier, preventing moisture from reaching the underlying surface. You will see a low percentage (under 5%) of water absorption if the material works well as a water-resistant barrier.

Polyurea and hybrids are non-porous, which helps prevent them from absorbing liquids. If water is absorbed and then freezes, it will expand and cause the coating to crack. High water absorption can also cause swelling, which results in dimensional change, loss of strength and adhesion, delamination, or fracture.

Water absorption will also tell you if a coating is suitable for interior and exterior use. A low absorption rate is necessary in outdoor applications, especially in climates with heavy rainfall or freeze-and-thaw cycles. If it has low water absorption, its strength and durability will be maintained over time with water exposure.

Water Vapor Permeability or Permeance

Definition: Water vapor permeability is the rate at which a material allows water vapor (water in its gas form) to pass through. It is stated in perms and is often also called permeance or breathability. Lower numbers indicate a lower permeability. It is not directly related to water absorption.

Importance: Along with water absorption, permeability can impact the performance and durability of coatings in waterproofing applications. A high permeability controls the rate at which water vapor passes through, preventing moisture build-up that could lead to mold growth, blistering, bubbling, and delamination.

Low permeability can also prevent corrosion, discoloration, and other forms of damage. If a coating with high permeability is applied to a metal surface, trapped moisture could accelerate the formation of rust. If the coating is breathable, the water vapor can escape, reducing corrosion.

Permanent Set

Definition: Permanent set refers to a point where irreversible deformation of the material occurs even after stress is removed. The property is recorded as a percentage of the total deformation compared to the original length.

Importance: Permanent set can be affected by various factors, including the type and amount of stress applied, temperature, and stress duration. Knowing a material’s permanent set will help you understand its behavior and properties under stress. It can be reduced by using materials with higher strength and stiffness and by controlling the temperature and duration of stress.

Cold Temperature Flexibility

Definition: Cold or low temperature flexibility is the ability of a material to resist cracking when flexed in low temperatures. This property is not listed for every material but will receive a pass or fail as a test result.

Importance: Though temperature and weather are out of our control, manufacturers can control how well their products hold up in these conditions. Polyurea and polyurea hybrids are unique because they withstand the fluctuating temperatures of various climates. Even in low temperatures, these coatings can maintain their durability and properties. Other materials might have impressive strength, but they can become brittle at low temperatures, which leads to cracking or failure.

Good cold temperature flexibility means the coating has enough flexibility and elongation to stretch without breaking over a mandrel bend. Flexibility is essential for the coating to expand and contract with the surface in low temperatures.

Adhesion Strength

Definition: Adhesion strength measures a coating’s resistance to separation from a surface when perpendicular tensile force is applied. It may also be called bonding strength. It is expressed in pounds per square inch and is typically tested for prepared steel and concrete surfaces.

Importance: Adhesion is one of the most, if not the most, important properties for a coating. It ensures that the material will adhere to the surface for long-term protection. It will do so even in the most aggressive conditions.

Polyurea or hybrids have excellent adhesion to several substrates, including concrete, steel, foam, and wood. Bonding increases with proper surface preparation. Cleaning the surface is always necessary to prevent adhesion failure. While not always necessary, priming the surface can provide the best adhesion results. Factors that may cause poor adhesion include temperature, cure time, moisture, and inadequate surface preparation.

Poor adhesion can cause peeling, flaking, blistering, and delamination, allowing substances to penetrate underneath. It can compromise the coating’s effectiveness in waterproofing, impact resistance, chemical resistance, and other properties. These problems can be costly to fix, so you’ll want to find a coating with good adhesion to your specific surface.

What Liquid Properties Are Important?

Unlike most manufacturers, VFI differentiates between physical and liquid properties. This differentiation helps tell you which properties pertain to the coating when it is in its liquid state vs its solid, cured state. Liquid properties help more during the application process, while physical properties tell you how it will perform throughout its lifespan. The following are important liquid properties:

Solids by Volume

Test Method: ASTM D2697

Definition: Solids by volume is a measure of the total volume that remains on the surface once the material cures, expressed as a percentage (%).

Importance: Low solids content means there is solvent within the product. Solvents evaporate as the coating dries and can be harmful to applicators since they may be volatile organic compounds (VOC). The evaporation of the coating significantly reduces the amount of material that cures on the surface. That’s why several coats must be applied to have the same thickness as a 100% solids coating.

A coating with high solids will have a higher concentration of solid components. They are more environmentally friendly because little to no solvents are emitted during cure. Also, they maintain the same level of thickness once cured. Not having to apply multiple coats means less material and less time are needed during application. There’s also a reduced risk of adhesion problems if extra coats are not required.

A great characteristic of polyurea and hybrids is that most are 100% solids. This makes applying them much easier because you know the amount of material you are putting down is the amount of material that will remain. You don’t have to worry about applying or buying more material to make up for the thickness that would evaporate if you used a low solid coating. Also, because there are no solvents, this contributes to a faster cure for reduced downtime and quick turnarounds.

A common misconception is that all solvents are VOCs. A common solvent that disproves this is water and it contains no VOCs. A solvent is part of the total solution and acts as a carrier for the entire system.

Mix Ratio by Volume

Definition: A mix ratio is assessed for liquid materials that require two or more components to be mixed together to produce a chemical reaction that will allow them to cure. Mix ratio by volume uses exact proportions, expressed as a ratio (ex. 1A:1B), measured using equal-sized containers.

Importance: Some coatings may have a mix ratio by weight, but due to the speed of polyurea and hybrids, there is not enough time to mix them together before they cure. They are applied by high-pressure spray rigs where the material is pumped through lines and mixed right at the gun tip so the reaction can occur without clogging the lines or gun.

Exact mixing proportions must be followed for proper curing. Too much or too little of one component can inhibit the cure. It might feel too soft or sticky and won’t offer the desired properties to protect a surface. It might never develop full physical properties, which wastes time and material if reapplication is necessary. Being off ratio could also affect adhesion and lead to peeling, flaking, or delamination from the surface.

Viscosity

Test method: ASTM D2196

Definition: Viscosity measures the resistance of a liquid to flow, or rather, the relative thickness/fluidity of a liquid. It will be listed on a technical data sheet in centipoise (cps) for each liquid component and sometimes for the mixed material. To better understand viscosity, below is a list of household items and their relative viscosities:

Importance: Viscosity can directly affect how a coating behaves during application. Because polyureas are applied by high pressure spray, they are most desirable at a lower and similar viscosity. The lower viscosity is desirable because it enhances the workability of the coating and makes application easier. The speed at which they are applied and their low viscosity can also reduce the amount of trapped air in the finish.

Low viscosity is also needed to evenly distribute the coating for smooth and uniform application. A higher viscosity would be desirable for brush applications because it prevents dripping and sagging.

Polyureas will not typically list a mixed viscosity. It’s hard to assess the combined viscosity while it is still a liquid because it cures quickly once combined.

Gel Time

Definition: Gel time is the time it takes for a material to stop flowing or become gel-like. A tack free time might also be listed for some products. Tack free is when the material is no longer sticky.

Importance: Polyureas and hybrids are incredibly fast setting, so their gel time typically happens within seconds of application. The speed is desirable for most users because the faster they gel, the quicker they cure and can be placed into service.

Their fast reaction time also means they are less likely to react with humidity and moisture in the environment. Low sensitivity to moisture allows them to be applied over cold or damp steel, concrete, wood, or foam surfaces.

Gel time can also affect the surface finish. As the material is sprayed, the gel time can make it come out fine and smooth or heavily textured. The texture can be further altered by adjusting the air pressure or gun tip size.

Their speed can also be a bit of a hindrance. Because they are so fast, they are a bit harder to work with. They are typically only sprayed through high-pressure rigs, and you must have adequate training to apply them effectively. The quality, thickness, uniformity, and texture may vary depending on the applicator’s experience. Sometimes, they can be slowed for a smoother flow on intricate surfaces.

Recoat Time

Definition: Recoat time is specific to coatings and is the time frame an applicator has to apply a subsequent coat or topcoat with ensured adhesion. It can also be called the recoat window.

Importance: Some coatings are applied in single passes, but multiple coats must be applied to build thickness. You must apply those extra coats within the recoat window. The longer the first layer cures, the less likely a subsequent coat will adhere to it.

If the recoat time passes, using a primer can ensure adhesion to the original coat. In some cases, roughing up the surface by sanding or grinding before applying the next coat can also increase adhesion. If you don’t adequately prepare the recoat surface, it can lead to peeling, cracking, or delamination between layers.

Place into Service

Definition: Place into service tells you the amount of time needed for a material to cure before it is ready for use.

Importance: For polyurea and hybrid coatings, the place into service time frame can be the same day (within 4-8 hours) or the next day (at least 24 hours). This is due to the speed at which they cure. Once they cure to a point where they have enough of their properties, they can be used.

The place into service time can vary based on application. If the coated surfaces will be in contact with chemicals, the material may need more time to cure. In other circumstances, such as truck bed liner, the coated surfaces might be ready for light use in a shorter amount of time, which can be desirable for faster turnaround.

Full Cure

Definition: Full cure is the time it takes for a material to develop full strength and properties for repeated daily use.

Importance: No material develops full properties upon initial cure. Most have to sit for a few days at room temperature to obtain full strength, hardness, and other properties listed on technical data sheets. This property is typically listed so users understand that failure can occur if too much pressure is put on it before it obtains its properties. Once the full cure time has passed, the material will perform as per the properties listed. Full cure can be affected by many factors, including temperature.

Where to Find Material Properties?

Once rigorous testing has been conducted on a product, our lab staff generates the physical and liquid properties. It’s important that customers can easily find properties for all our products. We list them on all technical data sheets and product pages. To find the technical data sheet, you can navigate to any product page, and it will be off to the right-hand side under the resources tab. For mobile users, the resources tab is at the bottom of the product page.

Contact VFI for more information on properties so you can find the best material for your project.

When to Upgrade a Qwik Spray Gun to a High Pressure Spray Rig

For those who have been spraying two-component polymer coatings for a while, you may be wondering if it’s time to upgrade your Qwik Spray Gun to a high-pressure spray rig. The Qwik Spray Gun is VFI’s cartridge-based spray equipment for use with specific coatings that have been on the market almost since the beginning of the company. In fact, we were one of the first to sell a cartridge-based spray system for spray on truck bedliner and EPS theming hardcoats. It has been desirable to many due to low maintenance, portability, and ease of use.

Even though the pneumatic cartridge gun comes with many benefits, there might come a time when you’ll need something else. There are several things to consider that can make the decision to switch to high pressure much easier.

Why Switch to a High-Pressure Spray System?

1. Better for Spraying Large Pieces or Areas

Maybe you started spraying small props, custom signs, truck beds, or other equipment but have since been offered bigger projects. VFI’s Qwik Spray Gun and similar cartridge-based equipment on the market are recommended for small to medium-sized projects. If you’re spraying a piece or area larger than 4×4 or 4×6 feet, a cartridge-based system will not be as efficient. The size of the project can be extended, but it is not recommended. These projects are also pretty flat, with a limited amount of detail.

Those who do use cartridge-based equipment on larger projects accept that they will encounter a lot of overspray. That overspray will cause more required post-work as the piece will probably need to be sanded, depending on the desired finish for the project. Otherwise, this can be avoided by spraying in smaller passes, but the application will be more labor-intensive and time-consuming.

2. Better for Increase in Project Volume

Another reason applicators typically stick to the Qwik Spray System is due to the amount they are spraying. This equipment is desirable for custom jobs where applicators work on one small project at a time or are only spraying a couple of times per month. It doesn’t make sense to spend money on an expensive spray rig. However, if you’re spraying more than you initially were, purchasing high pressure equipment can save you money in the long run due to material costs.

For example, businesses that spray less than 10 truck beds a month would benefit from spraying cartridges of VFI-544 Qwik Spray Bedliner, but if you’re seeing more traffic come through, you’ll probably need an upgrade to accommodate. VFI-542 High Pressure Spray Bedliner sprayed through high pressure equipment is recommended if your business is growing and you’re taking on more projects.

Also, high pressure equipment, because of the increase in pressure and temperature, cures coatings faster. A faster cure is extremely desirable for applicators who need to spray at high volumes so they can get onto the next project quicker.

3. Better if You’re in a Fixed Location

With the Qwik Spray Gun, as long as you have air pressure, you can take the equipment anywhere. However, if you’re not taking your spray gun to various locations for spray jobs, you don’t need portable equipment.

High pressure equipment is not as easily transported, which is why it’s not the go-to for many new sprayers or those who do low-scale, low-volume jobs. Once you know that the location you’re spraying at will be permanent and you have enough space, upgrading your equipment is ideal.

4. Increased Control

A downside of the Qwik Spray Gun is the lack of control when spraying. Once you pull the trigger, you must keep going until the cartridge is empty. If you were to stop midway through the application, the material would become clogged in the static mix tip because it is mixing the material as it exits.

While training is required to use high pressure equipment, once you get the hang of it, you have complete control while spraying. The trigger on the spray gun allows you to start and stop when needed. This is because a mechanical proportioner is typically used to meter out the correct ratio of material and mixes only what is necessary. It’s also desirable because it can pump, mix, and apply coatings with short pot lives very quickly.

5. Increase in Material Options

Not every material is offered in a cartridge-based format; in fact, most materials aren’t. The cartridge-based system, due to its low pressure outlet, is typically used for polyurethane and polyurea hybrid materials. However, urethane and polyurea hybrid formulas will not all work in the Qwik Spray Gun either. If you’re itching to try something new, you may need to get the application equipment to accommodate it. When you switch to a high-pressure spray rig, you get access to more materials and more formulas.

Polyurea is an incredibly fast setting material and requires high-pressure, high-temperature equipment to apply it. Cartridge-based spray guns typically only spray at a maximum of 100 psi and 10 cfm of constant pressure to push material through a static mix tip. If you use a fast material like it in a pneumatic, air-driven gun, the material wouldn’t provide a good mix without gelling and clogging the tip, so it would not have enough time to exit the gun.

6. Improved Cured Surface

While not exactly a catalyst for switching from a cartridge gun to high-pressure, there is also the benefit of having a more uniform, smooth surface. A downside of the Qwik Spray equipment is that you’ll never get as desirable of a finish as you would with high pressure equipment. Due to the lower pressure and atomizing tip on the cartridge, the material reacts more as it exits the gun. The Qwik Spray System’s reaction occurs slower, which allows the moisture in the air and the environment to create foaming. The foaming is the reason it comes out less smooth, with a bit of texture.

For example, the VFI-6171 70 D Qwik Spray Hard Coat is lighter and has a subtle splotchiness in its finish. In comparison, the VFI-6170 70 D Spray Hard Coat, sprayed through high-pressure equipment, comes out more uniform and slightly darker.

As mentioned before, if you are spraying VFI-6171 on larger projects, it will require more post-work than a high pressure spray. If the foaming reaction is not an issue for you, it’s best to stick with the Qwik Spray Gun, especially if your project size and spray volume have not increased.

High-Pressure Equipment Recommendations

VFI manufactures polyurethane, polyurea, and hybrid materials that are mostly applied using high-pressure industrial spray equipment. We recommend finding a high-pressure, plural component spray rig that can run at 130-155°F and 2,500 psi of constant pressure with high pressure heated hoses and 10ft whip hoses. Gun tips will vary by the project and will need to be adjusted on-site. The following machines are capable of meeting these specifications:

• Graco A-XP1 air sprayer (up to 3,500 psi, 170°F, 1.5 gal/min output, & 210 ft hoses)
• Graco Reactor 2 E-XP2 electric sprayer (up to 3,500 psi, 190°F, 2 gal/min output, & 310 ft hoses)
• Graco Reactor 2 H-XP2 hydraulic sprayers (3,500 psi, 190°F, 1.5 gal/min output, & 310 ft hoses)
• Graco Reactor 2 H-XP3 hydraulic sprayers (3,500 psi, 190°F, 2.8 gal/min output, & 410 ft hoses)
• PMC PHX-2 or 25 hydraulic sprayers (up to 3,000 psi, 190°F, 2 gal/min, 210-410 ft hoses)

Graco equipment can be used with Probler P2 or Fusion guns. PMC equipment can be used with AP-2 Air Purge, PX-7 Mechanical Purge, or Xtreme Spray Gun.

Whether you’re using the Qwik Spray Gun or high-pressure equipment, you must always wear proper personal protective equipment. Also, spray in a well-ventilated spray booth whenever possible.

Contact VFI if you need technical assistance when deciding if you should make the move to a high-pressure spray rig.

Understanding the Properties of Urethane Hard Coats

Understanding the properties of urethane hard coats is essential to picking the best material for theming projects. They are designed to harden surfaces like Styrofoam or EPS foam to protect architectural shapes and forms, custom signs, and props. If you’re new to hard coatings, you may not know what properties are essential to look at compared to other coatings. VFI has put together a comprehensive guide to help you learn more about them and how they function due to their properties.

What Physical Properties of Urethane Hard Coats Are Important?

Physical properties will tell you how the material will perform when cured. Most users look at these properties to help them decide if the coating will withstand the demands of their unique project. These properties are tested using standardized methods from the American Society for Testing and Materials (ASTM). The most prominent ones listed can include:

Shore Hardness

Test method: ASTM D2240

Definition: Shore hardness is a material’s resistance to indentation or compressive forces. It’s measured using a tool called a durometer and rated on various scales depending on the characteristics of the material. The most common scales for polymer materials are Shore A, which rates softer materials, and Shore D, which rates harder materials.

Importance: Hardness is a property that will tell you a lot about a urethane hard coat’s wear resistance, strength, and service life. It directly impacts the material’s ability to protect an underlying surface from scratches, abrasion, and other physical damage. A harder material will give more strength, while a softer material will give more flexibility.

Polyurethane hard coats most often use the Shore D hardness scale. They will typically be in the 65-75 D range, which has a similar feeling to a plastic hard hat. When they drop below this range, they feel more flexible or rubbery. When they go above this range, they will have high resistance to deformation but can also be brittle unless they reach a certain thickness.

Achieving a good balance of hardness and flexibility while also maintaining good weathering characteristics is important. Coatings with a higher hardness have less flex and can be more susceptible to cracking when applied to surfaces that expand and contract as temperatures change. Because they have less flex, they have a limit on substrate usage and are best applied to EPS foams for theming projects. Hard coats are not recommended for surfaces softer than themselves. However, other properties can contribute to them having more flex, even at a higher hardness.

Note: All VFI EPS theming hard coats list their hardness in the product name (ex: VFI-6170 70 D Spray Hard Coat) to help you find what you’re looking for.

Tensile Strength

Test method: ASTM D638

Definition: Tensile strength is the maximum amount of stress that a material can withstand before it fails when being stretched. It subjects a test specimen to an applied force or load until it reaches its breaking point. That force is then measured and expressed in pounds per square inch (psi).

Importance: Tensile strength is an important property that determines if a urethane hard coat is suitable for your application. It can tell you a lot about structural integrity and durability. Coatings with high tensile strength should be capable of withstanding significant force without breaking or deforming. They are often used to protect and support delicate substrates from heavy loads. Demanding applications that would require high tensile strength include EPS foam projects within touching distance of people.

The strength of a hard coat helps it maintain its integrity under stresses such as wind, vibrations, and pressure to prevent deformation. Even small impacts can cause stress, but high tensile strength helps it absorb those forces, preventing damage from occurring.

Elongation

Test method: ASTM D638

Definition: Elongation is a property that measures the percentage (%) increase in length of a material before it breaks when stretched. It has an inverse relation with tensile strength and uses the same test method (stretching force).

Importance: Elongation is a very important property for urethane hard coats due to their rigidity. Their job is not necessarily to resist stretching force, which is why they will have high tensile strength and low elongation. However, this property ensures some flexibility and complements the strength offered by hardness and tensile strength. It is the balance of all of these properties that allows hard coats to perform the way they are designed.

Elongation will provide some necessary give to the hard coat to resist cracking even with high tensile strength and hardness. It will absorb some energy from impacts and distribute stress more evenly. Elongation with a high tensile strength also provides thermocycling capability that would not be possible with high tensile alone.

Tear Strength

Test method: ASTM D624

Definition: Tear strength or tear resistance is measured by assessing the maximum force required to tear a material in a direction perpendicular to the direction of the stress. More simply put, it is a measure of how well a material can resist tearing. It is expressed in pounds per linear inch (pli).

Importance: Tear strength is another property that can tell you about the durability and lifespan of lower durometer urethane hard coats. In a hardcoat, tear strength is a hard property to obtain unless the coating is under 65 D, but it is a good sign for thermocycling if the tear strength is high with good elongation.

After damage has been endured, the tear strength will tell you how the material will hold up. It will also tell you about its resistance to rips, punctures, and cracks. Minor nicks, scratches, and cracks can be a starting point for bigger issues if tear strength is too low. Tear strength makes the coating more resistant to damage, preventing a problem from occurring that compromises its ability to protect the underlying substrate.

Elastic Modulus

Definition: Elastic modulus is a material’s resistance to elastic deformation when stress is applied. Elastic deformation is the temporary change a material goes through when under stress, so the material will return to its original shape or size once the stress is removed. This property is expressed in pounds per square inch (psi).

Importance: Elastic modulus is a material’s ability to bear loads without significant deformation (temporary bending or indentation), which can be very important for urethane hard coats. The stiffer the coating, the higher its elastic modulus will be.

A high elastic modulus will allow it to perform effectively by handling impacts and other forces without cracking, scratching, or denting. This is because these coatings can store more elastic energy before deforming. So, the hard coat will absorb the impact energy from a blow and prevent it from transferring to the substrate.

A lower elastic modulus will allow a coating to deform rather than crack. This is useful when an object might be kicked or something sharp will hit it. It will also allow the coating to deform and not break to protect the foam. This is also important if water and outdoor elements are a concern.

Impact Resistance Unnotched/Notched Izod

Test method: ASTM D256

Definition: Impact resistance is a test that measures a material’s resistance to impact from a swinging pendulum. Unnotched Izod tests do not make a premade notch in the test specimen, so the impact energy is focused on the entire test piece. Not creating a notch will test the overall toughness of a material. The value, in pounds per inch (lb/in), will be a less accurate representation of real-world impact situations and give an elevated number. An alternative test method is a notched Izod impact resistance test with a preset notch to accurately direct the force.

Importance: Urethane hard coated projects, especially ones placed outdoors, may experience sudden forces, shocks, or blows throughout their lifespan. Impact resistance provides an understanding of whether the material has the toughness needed to protect theming applications long-term. High impact resistance will help shield the substrate from damage by absorbing the blow, preventing the coating from cracking or chipping.

Softer coatings are better at taking impacts because they have more flexibility but have a low impact strength. Usually, softer coatings will not have an impact strength tested because they will flex out of the way and provide a low number as a result. However, impact resistance is only one property that will help determine the material’s toughness. Consider the tensile strength, hardness, and elongation for a better understanding of the material’s strength.

What Liquid Properties of Urethane Hard Coats Are Important?

Not all manufacturers divide up their properties between liquid and physical. VFI does this so our urethane styrofoam hard coating users know which properties apply to the material when it’s in a liquid state versus when it has fully cured. The following are liquid properties we typically list:

Solids by Volume

Test method: ASTM D2697

Definition: Solids by volume or volume solids is the percentage (%) of the total volume of a material that remains once cured. In the context of coatings, it’s how much material will remain on the substrate and how much will evaporate into the air.

Importance: The amount of volume solids lets applicators know how much material they’re actually putting down, which is important when trying to build it to a certain thickness. Some manufacturers specify a millage that must be applied to achieve optimal protection, so making sure you know what you’re putting down is that much more important.

Luckily, most urethane hard coats are 100% solids, meaning no material evaporates during cure. The amount of material you apply to a surface is guaranteed to be the amount that remains once cured. Because of this, you also don’t have to worry about calculating wet and dry film thickness using the solids by volume.

Note: Be careful of shrinkage on extremely long parts as it can change depending on your thickness causing your part to warp.

Mix ratio

Definition: A mix ratio is a ratio that entails the exact measurements needed from multiple components to be mixed to produce the needed chemical reaction for a material to cure (ex: 1:1 or 2:1). A mix ratio can be expressed in two ways:

• By weight: Uses an accurate scale to measure the amounts of each component needed to cure. This property will typically only be listed for hard coats that can be applied by brush or roller.
• By volume: Uses same-sized mixing containers to measure the amounts of each component needed to cure. This property will typically be listed for sprayable and brushable hard coats.

Importance: Urethane is a very touchy material. If you don’t follow the mix ratio properly, then it might not cure to the desired effect. Adding too much or too little of one component can make the coating feel sticky or goopy rather than plastic-like when it sets. Typically, when this happens, it won’t develop physical properties, so it cannot effectively protect the substrate it is applied to. Affected physical properties can include hardness, adhesion, and resistance to abrasion or impact. The coating might be softer and not adhere to the substrate, leading to peeling or flaking.

Incorrect mixing of the components can also lead to material waste. Not only are you wasting material from each mixed component, but you may also have to scrap the entire project you’re working on and start fresh. This problem can be costly as these foam pieces take time to carve, so you don’t want to mess up.

Off ratio material will also affect the final finish of the project. When you try to paint over a hard coat that has iso-rich spots, you might be able to get away with it. However, the paint might peel off more easily when placed in the sun. When you try to paint over a hard coat that has poly-rich spots, the paint might react more with the sun and cause the paint to bubble because it is not breathable.

Viscosity

Test method: ASTM D2196

Definition: Viscosity is a fluid’s resistance to flow or change in shape and describes the internal friction of a moving fluid. It is often referred to as the thickness of a liquid and is measured in centipoise (cps). Viscosity can be listed for each component (A and B sides) and the material when combined. To understand viscosity, here is a list of household items and their relative viscosities:

Importance: Viscosity will tell you a lot about how a urethane hard coat will perform. It determines how easily the coating can be brushed, rolled, or sprayed onto a surface. With a very high viscosity, they can be hard to spread evenly but prevent dripping or sagging. On the other hand, a material with a very low viscosity might not provide adequate coverage because it is too runny.

The ideal viscosity will depend on the application method and desired film thickness. When a material is applied by brush, the viscosity will be higher to allow easy application without excessive dripping or running. The higher viscosity also allows for better control when using this application method. When using spray equipment, lower viscosity coatings are required for even distribution, fine atomization, and a desirable finish. A similar viscosity A and B side is also highly critical to maintaining a nice even spray. Not considering the viscosity when choosing your application method can result in surface defects, such as brush marks, orange peel texture, or uneven coverage.

Viscosity affects the final thickness of cured coatings. Higher viscosity materials will generate a thicker film build, while lower viscosity materials will have thinner builds. A lower viscosity also ensures that the material can level and flow effectively to minimize imperfections in the surface finish.

Air bubbles are also typically generated in the application process. High viscosity materials are more prone to trapping air bubbles, which can create imperfections in the cured finish. Low viscosity materials allow more of the trapped air to come to the surface and escape before cure. Because the bubbles leave easier, you’ll achieve a smooth, uniform finish.

Pot Life

Definition: Pot life is the length of time a material can be used. Depending on the material, pot life can be as quick as seconds or as long as hours.

Importance: Pot life is not a property that is listed for every urethane hard coat. Since a chemical reaction happens much faster for spray coatings, you’ll see it as a property for brushable ones. It’s specific to these coatings because you need to know how much time you have to brush or roll the material onto the surface before it becomes unworkable.

Within the pot life window, your mixture maintains a viscosity for smooth and efficient application. Once the pot life ends, viscosity increases, making it hard to spread. Ensuring you have adequate time to apply the coating will minimize defects in the finish, such as orange-peel texture, air bubbles, and incomplete coverage. Also, mixing more material than can be used within the pot life leads to material waste. In some cases, mixing less material can even extend the pot life. Finding a coating with an acceptable pot life for your project is crucial for optimal protection over your theming project.

Tack Free

Definition: Tack free determines the amount of time after mixing that a material will no longer feel tacky (sticky). Depending on the material, this can happen in seconds or minutes.

Importance: Unlike pot life, this property is usually listed on sprayable coatings because it tends to happen shortly after the pot life. After a hard coat is sprayed, it needs some time to cure and become tack free so it will no longer adhere to dust, debris, or other objects that come into contact with it.

This property is essential to know for handling and assembling a coated project. If it is still tacky, it can pick up contaminants that compromise its appearance and performance. These contaminants can come from airborne dust or someone touching the surface before it has solidified enough. The material then traps these particles, marks, or smudges once cured.

Most users will want a fast tack free time. The speed will allow further processing, such as sanding or painting, to occur much sooner. It also helps if the coated component needs to be assembled with other parts. The faster an applicator can post-work their project, the faster their production cycles are. However, a fast tack free time can limit the working window, especially for larger projects.

Note: A long tack free time also creates a great window for recoating and will help with better adhesion. Always check your technical data sheet (TDS) for recoat windows to prevent bad adhesion or additional sanding.

Cure to Handle

Definition: Cure to handle is the time until a material can be handled after application. It usually comes between the tack free time and the recoat window since the material has not completely cured. Most cure to handle times happen minutes after application.

Importance: Cure to handle time directly affects how soon you can handle a coated object after application. It can also tell you how soon it is ready to be sanded, painted, or assembled without compromising the final properties.

It needs sufficient time to cure and develop its properties. If you handle the coated project too early, the surface can crack or become damaged by touch. Handling it too soon can also lead to uneven curing, weak spots and inadequate protection of the underlying surface. Different urethane hard coats will have different cure to handle requirements.

Recoat Window

Definition: The recoat window is a property specific to coatings as it is the time frame between which a previous application can receive a subsequent coat or topcoat. Depending on the coating, a recoat window can extend from minutes to hours and may have different requirements based on the specific formula.

Importance: Some urethane hard coats must be applied in layers to build the thickness. Adding layers is usually done for more adequate protection of the underlying surface. During the recoat time, you can be sure the subsequent coat will have excellent adhesion with the prior one. This property is also important if you must paint over the coated surface for theming purposes. You can be sure that the paint will stick to the hard coat.

If you apply a new coat outside the recoat window, there will be weak adhesion between the coats. That weak bond can compromise the overall integrity of the coating, making it more likely to peel, crack, or delaminate. Poor adhesion can also compromise scratch resistance, impact protection, and other properties. In some cases, the initial coating can be sanded or scuffed to create better mechanical adhesion for the second coat. A strong bond between them will allow them to perform consistently across the entire project.

How to Find Urethane Hard Coat Properties

Because material properties are so important for users to know before they purchase a product, we display them accurately after meticulous testing and review. They can be found on technical data sheets or product pages of any product. Technical data sheets can be found under the resources tab on any product page.

Contact VFI if you would like more information on properties to determine the best product for your project.

Sprayable Plastic Coatings for Theming & Attractions

The main job of a sprayable plastic coating for theming and attractions is to protect foam surfaces from various environmental elements. When you create a new themed environment out of EPS or Styrofoam, you’ll want it to last. That won’t happen unless you have the proper protection. Even though this part is unseen by the audience, it’s one of the most important steps. This step also prepares the surface for priming and painting to create a more uniform and professional finish. So, you need to find the best material to do so.

What Is a Themed Environment?

Themed environments are physical spaces that should transport guests and visitors to different times and places. An effective way to do this is by creating an immersive world using architectural sets, lighting, sound, and technology. If done right, your environment should invoke emotion, engage the senses (sight, hearing, touch, etc.), entertain, and give your audience a reason to want to come back.

These themed environments can help businesses differentiate themselves from the crowd. An environment like this can also foster a good work culture. Businesses can even get brand exposure from people taking pictures or videos and sharing them online, helping bring in more people. Themed environments are not limited to theme parks like Disney World and Universal Studios; you can create a unique experience for showrooms, restaurants, stores, and more as well.

What Makes up a Themed Environment?

Just about every part of queue areas, theme park rides, and even the streets of a theme park can be themed. Theming elements can be as simple as faux rocks and trees or as extravagant as large 3D sculptures. The following are used to add to the overall theme in amusement parks:

• Sculptures: While not always directly surrounded by an environment they’re meant to be in, theme parks can use larger-than-life 3D character sculptures throughout the park to further connect with guests, elicit nostalgia, and generate photo opportunities.
• Props: Many theme parks, as added entertainment, put on stage productions that use various stagnant and handheld props. These props create much-needed visual elements for stories. Without props, costumes, and sets, much is left up to the imagination. When props are used, it further enhances the imaginative experience.
• Scenery: The architecture is meant to engulf your audience in a new world with visual elements that captivate them the second they enter. Setting a scene can include a handful of things, including simple architectural elements like columns, shutters, crown molding, etc. or, memorable objects, sets, and characters that tell a story.
• Signage: Signs are typically the first thing an audience sees as they approach a building. They may even help them decide if they want to continue into a location, whether that be a shop, restaurant, or ride. It also directs them where to go since they’re high up in places everyone can see.

How to Design a Themed Environment?

The type of materials you use to create a themed environment will depend on several factors, including:

• What is your budget?
• Will the project be for indoor or outdoor use?
• Will people be able to touch it?
• Is it a one-time project or long-lasting?
• What are your safety requirements?
• Is there a weight requirement?

While various materials have been used to create themed environments in the past, it has become much more common for designers and artists to use foam to make massive landscapes, sculptures, signs, and more. This material is desirable because of its cost-effectiveness and lightweight nature. Compared to other building materials like natural stone, wood, and metal, foam is much more affordable and easier to move or transport to a permanent location.

The most common foam used in these instances is EPS (expanded polystyrene). XPS/Styrofoam (extruded polystyrene) and polyurethane foam have been used as well. EPS is much easier to cut, shape, and mold using CNC, hot wire cutters, and wire brushes, among other tools. This method allows designers to create pieces with less skilled artistic labor and more easily than if they used heavy, solid, and expensive materials.

How to Protect EPS Foam Theming Projects

While foam is an excellent material for theming, it can’t be placed in an environment without a protective shield because it’s not very durable. Without protection, it would be exposed to the sun, wind, rain, and other weather conditions that could cause damage. The foam could also become damaged from transport or during installation if unprotected. Also, if you want to be able to sand, prime, and paint the foam, a rigid material that creates a smooth surface is needed. The best thing to do would be to harden the foam.

A sprayable plastic coating like urethane is a good material that hardens and protects foam for indoor and outdoor use. It is versatile and can be formulated with varying properties, including Shore hardness and tensile strength. The recommended durometer is around 65-75 D and will provide a plastic-like appearance and feeling while not being able to shatter or crack.
When undertaking large-scale projects or many small projects, the best application method is by spray. There are two distinct spray methods VFI recommends:

• High pressure – For high volume projects, artists and applicators use a sprayable plastic coating through a two-component high pressure spray rig on large projects. VFI recommends VFI-6170 70 D Spray Hard Coat, as it provides a durable shell over large structural shapes made with EPS foam. A benefit of this material is that it is Class A fire tested to meet strict indoor and outdoor safety standards.
• Qwik spray – An alternative to expensive spray equipment is to find a sprayable plastic coating formula that is applied with a cartridge-based applicator gun. This method is best for portability if you must take your projects on the go. It is also only recommended for smaller projects under 4 feet. Otherwise, you’ll have to spray in much thinner passes and must be comfortable with the overspray it will generate. VFI-6171 70 D Qwik Spray Hard Coat is VFI’s cartridge-based hard coat compatible with the VFI-7500 Qwik Spray Gun.

Interested in a brushable hardcoat? Check out VFI’s blog for more information.

Benefits of Using a Sprayable Plastic Coating

While foam is lightweight, the coating is also fairly light, so it doesn’t add too much weight to the entire piece, making it just as easy to move and transport finished objects. This solves a lot of logistical problems with large pieces that have to be hung up or mounted above the ground.

Because the coating forms a seamless finish, it is able to withstand damage from weather, which is essential if the foam piece is placed outside. Its hardness makes the foam incredibly strong and resists cracking, so it’s capable of lasting long-term. It is also impact and abrasion resistant, so it holds up in the event that people are constantly touching, leaning against, or sitting on it, which is expected in theme park environments where children are present.

Polyurethane, as a sprayable coating, is incredibly versatile in what it can be applied to. It conforms to curves and does not diminish details as long as it is not sprayed on too thick. While the finish typically comes out smooth, it can be sanded to enhance aesthetics before applying a paint or top coat.

Contact VFI if you are interested in any of our EPS theming hard coats and need assistance choosing the best one for your project.

What Is Polyurea Hybrid?

Polyurea hybrids have been closely confused and mistaken for a polyurea. While they have some components of polyureas, they are vastly different in some major categories, including price, properties, and moisture sensitivity. They are generally two-component systems where a blend of polyols and amines react with an isocyanate.

The chemical backbone of a hybrid is composed of both urethane and urea linkages. These linkages are made of a reaction of amines with isocyanates (urea) and polyol with isocyanates (urethane). However, not all hybrids are equal. Some formulas can be 99% urea linkages to 1% urethane mix, while others can be the complete opposite at 99% urethane to 1% urea. These content variations will change the properties and other features substantially.

Urethane linkages contribute to a more favorable price point compared to polyurea. The amine content, linked to polyurea, makes it less sensitive to moisture compared to urethane, because it does not require catalysts to promote a water reaction. Pure formulations are very limited in the compounds they can use for the B-side. A hybrid’s urethane side allows for more versatility.

They can be specially formulated into tough, elastomeric coatings for industrial and commercial applications. They can handle complex designs over surfaces, such as metal, foam, and concrete when applied by spray. Most are aromatic in nature, which means they do not resist UV rays.

Hybrid vs Polyurea vs Polyurethane

Hybrid Advantages

• Their fast-setting ability makes them suitable for spraying on horizontal and vertical surfaces. Some formulas are also capable of being sprayed overhead without sagging. This fast-curing time also provides projects with a quick return to service.
• These coatings are tough and durable, with properties that allow them to resist impact, abrasion, wear, and tear. Other properties that help them resist damage include chemical and corrosion resistance.
• Using a spray-applied method, the material creates a seamless film. Since there are no seams, the coating prevents water penetration that could cause damage to the underlying surface.
• Since these coatings are very versatile, they can be adjusted to fit the needs of the application. Hardness can range from 40 to 75 D on the Shore Hardness scale, which is rubber-like to extremely hard.

How Is It Applied?

Proper preparation of the substrate is important to ensure the coating will perform how it should. Moisture and humidity should be monitored as they could cause issues in the application process.

The two-component materials are typically mixed through a proportioner. With either high-pressure, low-pressure, or cartridge-based spray rigs, the coating is sprayed directly onto the surface to protect it from external damage. Temperatures and pressures of the machines must also be taken into consideration.

• High-pressure spray rigs are the most common application method. They are plural component machines capable of heating the material and maintaining a specified psi. This equipment is best suited for high-volume and continuous coating applications. Vehicle producers, film-set creators, and theme-park sculptors typically benefit from these systems.
• Low-pressure spray rigs are used when coatings have slower gel times and longer cure times. The longer cure time allows easier spraying when going through a machine, using less pressure to push the material. Sometimes, it’s not necessary to have an expensive high-pressure rig, especially if you have flexibility in your project timeline.
• Cartridge-based spray systems offer the benefit of being able to spray while being less of an investment. The cartridges make the application portable and suitable for lower-volume applications. Based on frequency of use, a vehicle repair shop would benefit from cartridge-based coatings, whereas a vehicle manufacturer would probably need a high-pressure system. The maintenance on the machine is also much easier than a high-pressure system and does not require skilled labor to maintain.

Common Polyurea Hybrid Applications

Since hybrid coatings are highly customizable, they are the best choice for a wide range of applications. With a good cost-to-benefit ratio, they’ve been used in the following commercial settings:

• Below-grade waterproofing. The coating creates a seamless, leak-free membrane, which makes it a suitable option for waterproofing surfaces. With fast-curing properties, it is much faster and easier to apply than other materials. The barrier not only protects a building’s foundation against moisture but also against other contaminants in the ground.
• Tank pad coating / secondary containment. Hybrids work to create impermeable barriers in areas where preventing hazardous materials from reaching an environment is critical. These coatings are highly resistant to chemicals and solvents, so in the event of a spill, they keep the material contained. They work great over EPS foam for tank pad coatings.
• Truck bedliner. At a relatively low cost, hybrids form a durable, water, and air-tight barrier for exterior protection of pickup trucks, dump trucks, and utility vehicles. These spray-on coatings are easy to clean and maintain with the bonus of abrasion, scratch, and skid resistance. They are your best bet for vehicle part protection, especially from rust and corrosion.
• Theme park and decorative design. The coatings can form hard shells over EPS foam, wood, and other structures that need long-term protection from abrasion and physical wear. Sculptors and set makers have used them to make characters, artificial rocks, themed environments, and more.
• Joint filler. They also make great materials for filling concrete joints in industrial and commercial settings. Rather than spraying, they are injected into the cracks between concrete panels and cure quickly for a fast return to service. They are excellent at protecting concrete joint edges from damage due to heavy traffic.

VFI High Performance Polymers

VFI manufactures a handful of coatings for industrial and theming projects. From our bedliners (VFI-542, 543, and 544) to our specialty coatings like VFI-206, we have options for any circumstance. Also, ask about our polyurea coatings for other industrial applications. If you don’t see something you’re looking for, contact the VFI team for assistance.

Cast Stone vs Manufactured Stone Veneer: Which Should You Use?

You may think the architectural elements you see on commercial and residential buildings are made of real stone, but it is becoming more common for them to be made of concrete. It is hard to tell if an accent wall in a lobby or the columns on a front porch are made of natural stone because man-made products are so realistic.

For years, natural stone was upheld as a premier building material for its beauty and stability. The reason why people are turning to other building materials is due to cost, weight, and sourcing difficulties. Manufactured stone and cast stone were created as solutions to these problems.

What is Natural Stone?

Natural stone is a durable material that is obtained from the earth. It has been used for centuries due to its strength and longevity. To make it an effective building or decorative material, it is cut down, shaped, and finished for an assortment of projects. Though, it is much more difficult to cut than man-made products.

A desirable feature of natural stones is their uniqueness. As a product of nature, no stone will have the exact same pattern, look, texture, or coloring. There is an abundance of natural stone types, including limestone, granite, marble, slate, etc. While each natural stone’s distinct graining and coloring give it character, it prevents uniformity and consistency throughout a project.

What Is Natural Stone Used for?

• Natural stone was once used to create some of the most famous historic structures, monuments, and sculptures around the world, and still is.
• It can be used as decorative architecture on interior or exterior floors and walls. An example could be an accent wall or a fireplace.
• For larger outdoor projects, it can be added to your landscape when designing fishponds, patios, outdoor kitchens, or boundary walls, among other things.
• Natural stone can even be used for furniture like countertops or showers to give your home a makeover. Granite and marble are most favored for these projects as they create elaborate displays that are easy to clean and maintain.

What Is Cast Stone?

Cast stone is a man-made concrete building material whose main purpose is to replicate natural stone at a lower cost. It is used to create complete architectural elements. Cast stone is often mass-produced, meaning you’ll likely find identical pieces across one project, which creates a uniform appearance with consistent quality. Its availability is also not limited by geographical factors, which means it is accessible wherever you are.

It has unmatched design flexibility as it can be molded into various shapes and sizes to achieve your desired aesthetic. It can also be pigmented to match and blend with other building elements. Cast stone can have intricate details, replicating diverse textures, shapes, and patterns without the need of skilled labor carving the shape each time.

Because it’s made of a synthetic material, it often costs less and is lighter than natural stone. As a lighter-weight material, transporting and maneuvering concrete pieces on a site is much easier, especially for larger projects. The manufacturing and installation processes are easier, with less time and labor needed. And even though it is lighter, it is still durable and has high strength as a concrete product.

How Is Cast Stone Made?

Cast stone can either be wet-cast or dry-cast concrete. The wet cast method is commonly used for casting large, structural, and complex elements. A mixture of Portland cement, aggregate, and pigments is combined and poured into molds. The texture of the material will be similar to natural stone and produce finishes that are difficult to distinguish from the original material.

Cast stone can be molded using various materials, including wood, fiberglass, plastic, or rubber. The material you should use depends on the architectural element being replicated and the amount of detail required.

One of the best mold materials is liquid urethane rubber due to its abrasion resistance and tear strength. It handles concrete well without breaking the cast piece and can produce as many as 100 pieces in a single mold with the same consistent detail.

By first casting over an original model, these molds will easily replicate the original piece’s features into the concrete. Due to their flexibility, they are also great for elements with deep undercuts. For most cast stone projects, a 20-30 A material is recommended to obtain desired shapes and details.

What Is Cast Stone Used for?

• It is often used in architectural restoration projects because it is able to replicate and replace the old and deteriorated stone on historical buildings.
• It is popular for decorative elements, trim, ornaments, or facings for buildings and other structures, such as columns, porticos, balusters, pier caps, copings, watertables, window surrounds, door entries, and more.
• It makes great concrete furniture and décor, including tables, benches, plant pots, etc.
• It is found on and in homes, condos, churches, banks, courthouses, and more.

What Is Manufactured Stone?

Manufactured stone veneer is often called a handful of other names, including faux stone, artificial stone, or cultured stone. Like cast stone, it is a man-made material designed to replicate the look of natural stone at a lower price and weight. It differs from cast stone because it is veneer, a thin layer of molded concrete applied to another surface, like wood or flat concrete. It is often used for non-load-bearing decorative detailing, as it does not provide any structural support.

Stone veneer products offer an array of shapes, sizes, and color options that are indistinguishable from natural stone unless closely inspected. As a concrete material, they are strong and durable to be used in indoor and outdoor spaces.

They are not the same thickness and weight that a natural stone would be, making them easier to install in hard-to-reach places. A faux stone can be 15 pounds or less with no support needed when applied to various surfaces.

How Is Manufactured Stone Made?

Manufactured stones are typically pre-cast using wet-pour concrete. Like cast stone, they are made of water, cement, superplasticizers and lightweight aggregate materials. This mixture makes them durable and able to withstand the elements. It is the coloring and molding of the concrete that makes them look like natural stones. When poured into molds with pigment, the concrete mixture is able to resemble marble, granite, limestone, and other desirable stones.

The actual process begins by making a mold. The mold is typically created as the negative of a real stone, so the concrete can mimic the look and texture accurately. When urethane molds are used, the veneer stone will pick up all the details of the stone it is replicating. When making the molds, a 30-50 A urethane material is recommended, as it provides more strength than a lower durometer rubber would.

A small mold of one stone can be made, as well as a large mold with multiple stones that vary in size, which are then packaged together. As a veneer, it is typically cast at about 1 inch thick. Some of the stones will have repeated textures and designs, but that ensures your project will be consistent in quality and appearance.

Manufactured stone veneer will have a flat back for easy installation over a variety of surfaces. While cast stone is typically custom-made, manufactured stones can be laid out and cut to suit the project.

What Is Manufactured Stone Used for?

• The main use of manufactured stone veneer is to create exterior facades and unique statement walls.
• They can be used both indoors and outdoors to elevate the architecture and appearance of office buildings, restaurants, roadways, hotels, medical facilities, etc.
• Due to their flat-back nature, they can be installed over metal, wood, masonry, brick, or poured concrete to add a decorative element to various spaces.
• They are used to elevate the architecture and appearance of various buildings. They can be placed around fireplaces, fire pits, outdoor kitchens, water features, walkways, patios, and more.

If you’re interested in cast stone or manufactured stone, VFI makes a variety of 2 part urethane rubbers that make perfect molds for these projects. Contact us today for assistance in finding the best material.

Urethane Molding and Casting Materials

Industry professionals can greatly benefit from various molding and casting materials when it comes to making structural and architectural concrete elements. Among some of the best materials to use are urethane rubbers.

They are very versatile two-component kits that can be used to make molds, formliners, and stamps for sturdy, functional, and artistic concrete projects. Their versatility comes from the ability to be formulated with varying properties, including a range of Shore hardnesses, which allow the materials to be used for small, detailed projects as well as large structural projects.

What Is a Concrete Mold?

Concrete molds, also called forms, are a type of molding and casting material used to shape fresh, liquid concrete. Once hardened and left to strengthen, these concrete pieces are demolded to be used as building components, decorative elements, or artistic displays.

A concrete mold must be sturdy and abrasion-resistant to ensure it won’t deform during the casting process and the concrete will demold without damage. Molds can be made of various materials, including rubber, plastic, silicone, latex, wood, and metal. Urethane rubbers are among one of the most robust materials for concrete casting. These molding and casting materials can be made into a range of shapes and sizes with various designs and textures. These details are transferred into the wet concrete to influence the final finish of the piece.

The hardness of the mold is an important factor to consider when casting concrete and depends on the piece you intend to produce. The softer the rubber, the easier it will release from a complex, detailed concrete piece. However, softer rubber is not as durable as harder rubber. As urethane’s hardness increases, it is less flexible but more durable. This is why more detailed stone molds (ones with more incuts and the need to compress) use 20-50 A material and large form liners and stamps use 70-90 A material.

How Is It Used to Cast Concrete?

A single urethane mold can be used to make repeated concrete castings that mimic natural materials. It captures high surface detail and can be reused over and over, making it the material of choice for high-volume production. These molds are used to cast concrete in many different ways, including:

• Precast panels – Harder rubber is typically used to make larger structural elements. The concrete material is poured into massive flexible form liners off-site, in a controlled environment. These detailed liners can then make decorative panels, fences, retaining walls, and more.
• Manufactured Stone – Rubber ranging from 30-50 A is great in general assembly lines to make molds for lightweight concrete stone facades and/or decorative exterior elements. Urethane rubber’s dimensional stability is perfect for the repeated casting process required. These stones are used on homes, restaurants, and more.
• Cast Stone – Urethane rubber is made primarily for wet cast stone and is used to create corbels, wall caps, crown molding, and other advanced shapes. Urethane rubber is mainly used in cast stone when compression of the mold is required.
• Hardscape – Rubber stamps or rollers are capable of turning wet concrete into natural-looking, textured pieces that mimic real brick, flagstone, slate, etc., for outdoor decks, patios, walkways, and more. Rather than using expensive natural stone, stamping concrete with urethane can create pavers, steppingstones, small retaining walls, and curb walls for less.
• Décor & furniture – Concrete can be cast into molds to make large statues or art pieces for decoration or even functional elements like benches, countertops, planters, fireplaces, and outdoor kitchens. These creations can utilize stone veneer as a finish or cast stone for complete pieces.
• Architectural Restoration – Softer urethane rubbers are great for restoring old stonework on buildings. The lower durometer makes it easier to demold around complex shapes and undercuts without damaging the original piece.
  Whatever your project is, it is important to use an appropriate mold release when casting concrete. While urethane is an extremely durable material, it can also create strong bonds with many surfaces.

Not using release can have disastrous effects on the mold and concrete pieces. Even with a release, you may have to use a tool to pry the piece out of the mold if it’s stubborn. VFI, however, has developed new easy-releasing urethane rubbers for ease of use and reduced breakage when used with release.

Are there Alternatives to Urethane?

Choosing the right material is essential to ensure it will meet the needs of your project. And while urethane does come with great benefits, there are alternatives that might be better for your application. Other materials must be non-porous, non-reactive with concrete, and rigid enough that the mold won’t change shape once the concrete is cast.

1. Silicone rubber molds

Silicone is another flexible molding and casting material that produces intricate designs and textures on concrete elements. It has outstanding demolding characteristics that don’t require mold release. It works well for architectural restoration since it is able to keep the original model intact without damaging it.

However, polyurethane has more variety when it comes to hardness so it can be used in a variety of concrete applications that silicone may not be able to. Silicone is also more expensive and not great for large-scale, high-volume concrete casting. Shrinkage is another major concern with silicone when repeatedly casting concrete.

2. Plastic forms

If you desire a more affordable material, various plastics like ABS have been used to cast concrete for decorative and artistic pieces. They can offer high detail in the cast part, producing complex shapes and fine textures. They are also relatively easy to use due to their lightweight nature. However, making these molds requires certain skills and techniques you don’t need with urethane. Most plastic molds will need to be purchased from a manufacturer and will have a preset design. They also will not last as long as other materials, producing only about 10 castings per mold.

3. Wood forms

Wood molds can be custom-made and are easy to construct for large-scale structural elements. They are versatile, tough, and strong, and because wood is readily available, they can be more affordable for certain projects. However, these molds are not as durable as other materials and are not suitable if you want intricate designs or curves in the concrete. To increase the usability of these forms, a form coat epoxy can be used to protect the casting surface from abrasion.

4. Metal forms

Most metal molds are made from either steel or aluminum and can be used for structural or decorative concrete purposes. They are durable, made to last, and, like wood, produce smoother finishes. Similar to making plastic molds, metalworking requires specialized tooling and skills for precision. Metal is ideal for repeated, high-volume use when making concrete pieces for larger industrial projects that require strength and durability over aesthetics. Most metal molds will be small because of cost restrictions. A form coating epoxy can be used for long-term protection of these forms as well.

5. Latex molds

Because of its low viscosity, latex is applied to a model by brushing on multiple thin layers until the desired thickness is met. Having to apply multiple layers is a big drawback to using this material. Some latex molds can take as long as 2 weeks to finish because they don’t cure as quickly as silicone or polyurethane. So, if you require quick production, this is probably not the material you want to use. Also, due to latex being used as a thin film, you will always need a rigid backer mold for casting. However, it is probably the strongest and most resilient material, leaving you with long-lasting molds for years.

Why is Polyurethane Rubber Better?

• It is a long-lasting, reusable molding and casting material. Due to its high abrasion resistance and strength, it is more durable than other materials.
• It creates highly detailed and accurate concrete pieces that mimic natural materials. With high flexibility, the material is able to form around complex undercuts and other details to make perfect copies of the original.
• It is easy to work with. While it requires a release agent for demolding, it requires little effort to separate it from delicate details once the concrete has set. There are also easy-releasing urethanes available at VFI, which makes using these materials more desirable when heavy release cannot be used.
• It can be a cost-effective option compared to silicone and metal molds. Silicone has a few benefits that urethane lacks, but they’re fairly equal in their abilities. While it is more expensive than wood or plastic, it makes up for that cost in its longevity, flexibility, and reusability.
• It is an extremely versatile material that can come in a range of hardnesses to complete both large and small projects. There’s really no limit to what urethane molds can be used to create.

VFI manufactures a variety of urethane rubbers for various concrete casting projects. Contact us today if you need help finding the best material for you.

What Is a 2 Part Polyurethane Rubber Kit?

A 2 part polyurethane rubber kit, or 2K polyurethane, is commonly used in the construction industry as a molding and casting material or precast concrete product. The material is packaged into two separate containers, which are meant to be combined just prior to use.

Most urethane rubber kits are categorized in terms of hardness. Since urethane rubbers are called elastomers, they use the same hardness scale, which is the Shore A Scale. A lower number on the scale means a softer, more flexible rubber. A higher number on the scale means a harder rubber that provides greater durability and long-term use. Soft rubbers are best for making molds with complex shapes or details, while hard rubbers are best for making tough, flat molds, formliners, or stamps.

2 part polyurethane rubber kits are excellent for casting concrete. They are mainly used to make molds for manufactured stone, cast stone, sculpture and décor reproduction, architectural restoration, and more.

Why Does Liquid Urethane Rubber Come as a Kit?

Urethane rubber comes as a 2-part kit because it requires precise mixing of each part so it can undergo a controlled chemical reaction to cure. The kit includes an A side and a B side; the A side is an isocyanate blend, and the B side is a poly/amine blend. Mix ratios of the A and B side materials can vary, with 1:1 or 2:1 by volume being the most common.

The chemical reaction can only occur once the A side and B side components are combined and mixed. When mixed, the two components chemically link, creating an irreversible exothermic reaction. The material will cure at room temperature to a flexible rubber with formulated properties. Being a liquid material at the start allows you to mold it into any shape you require.

Advantages of using a pourable urethane rubber kit include:

• Ease of use: 2 part urethane rubber kits are easy to use, as many users like to measure their material by volume, so no scales are required.
• Controlled pot life: By keeping the components separate until use, you can prepare everything else for molding before you pour the rubber.
• Controlled cure time: Since the components are separate, they won’t start curing until they are mixed. You can ensure that your material will cure at the desired rate for your application.
• Custom formulations: Varying the ingredients and the mix ratios of the two components creates different formulas. This allows for versatility in properties to meet requirements for various applications. Flexibility in formulation is much easier to achieve with two component kits.

How Do You Mix the A Side and B Side?

Before mixing, ensure your material, mold boxes or forms, and working area are at a proper working temperature. At VFI, we typically recommend temperatures above 65°F for the material to cure properly. Always check the technical data sheet provided by the manufacturer for specific instructions.

Not all urethane rubber products have the same mix ratios or handling procedures. Check the mix ratio before you start, as they can be listed by volume or weight on the technical data sheet. Following the mix ratio is crucial for your material to achieve the full formulated properties once cured.

Before mixing, prepare the equipment you’ll need. Spray release on your mold box or form for ease when demolding. We recommend having two clean, dry mixing containers, such as plastic buckets, and a hand mixer or mixing sticks. Depending on how you plan to measure your material, you may also want a scale. Also, wear proper PPE, including gloves and safety glasses, to avoid contact with the material. Once you are set up in a well-ventilated area, proceed with the following:

• First, mix the B side. Some B side material may have settled in transit or storage, so we require mixing before pouring it into a clean container.
• Weigh or measure the B side into a clean mixing container.
• Weigh or measure the A side and pour it into the same mixing container. Once the A side material has been added to the B side material, your work time/pot life has begun.
• Mix the A and B sides together using a hand mixer or mixing stick. Make sure to scrape the sides and bottom of the container while mixing to ensure a homogenous mix. Mix slowly to prevent air bubbles from forming in the material.
• Pour the mixture into a new, clean container for a second mix. The double mix method will ensure that no unmixed material is used. Continue to scrape the sides and bottom while mixing.
• After thorough mixing, the rubber should be immediately poured into a mold or form to cure.

If you do not use all your material, a nitrogen purge can help extend the shelf life of both the A and B sides. Do not save any material that has already been mixed. Only unmixed A and B sides can be purged.

How is 2-Part Urethane Different?

A 2 part polyurethane rubber kit allows for versatility and customization that other single and two component materials can’t provide. Chemistry can be adjusted to provide different properties, making them suitable for applications in various industries.

Urethane’s properties contribute to an increased lifespan of molds and forms made with the material. It has better abrasion resistance with excellent strength, durability, and dimensional stability. These properties are why urethane rubber is one of the most commonly used materials to cast concrete.

Its elastomeric properties allow it to be bent or compressed and still return to its original size and shape. This flexibility is vital for abrasive molding conditions since it results in less damage to the mold and casting. VFI has even developed a Max Release Molding Rubber series for easier demolding and reduced breakage rates. This is similar to the characteristics of silicone, but much better for concrete casting.

Also different from other materials is urethane’s ability to provide consistent performance under repeated casting. Many materials are only good for a few uses, while a single urethane mold is capable of producing up to one hundred castings. They are also typically less expensive than other similar rubber kits like silicone.

How Do I Find a Liquid Polyurethane Supplier?

The first step in finding a liquid polyurethane supplier is to conduct an online search. Search engines like Google can offer a vast amount of information when searching key terms like “liquid polyurethane rubber suppliers.”

Attending trade shows, exhibitions, and conferences is also a great way to connect with polyurethane manufacturers and suppliers. Look for events related to industries where the material is typically used. These events will generally have polyurethane companies showcasing their products so you can connect with them or other professionals who use the material.

Alternatively, you could also reach out to professionals in your industry who may use polyurethane. They may be able to guide you in the right direction or recommend reliable suppliers based on their experience.

VFI is a manufacturer of urethane rubbers, plastics, and coatings. Contact us today if you’re interested in hearing more about our products.

Advantages of Using a Form Coating Epoxy

There are several advantages of using a form coating epoxy over expensive precast forms, surfaces, and molds. Forms are essential for casting concrete, as they hold and shape the wet material as it cures. However, if you want to repeatedly use these forms without damaging them, you’ll need to apply a form coating. This protective coating will contribute to the long-lasting success of the casting surface.

With an understanding of how to use a form coating epoxy to protect surfaces from abrasive damage, you can create an abundance of quality precast products from a single surface or form. Here are several advantages:

• Extended protection – Using an appropriate form coating epoxy will ensure that the surface can withstand the weight and abrasive characteristics of the casting material during the pouring and demolding process. While rigid, it is also formulated with some flexibility so it will limit cracking without fabric or polyester reinforcement. The coating minimizes abrasion, impact damage, wear, and chemical or moisture exposure to enhance the quality, durability, and life of the surface.
• Reusability – Some materials are more durable than others. After repeated use, the casting surface can deteriorate. When a form coating epoxy is applied, it makes the surface durable, lengthening the life of the form so it can be used over and over without damaging the underlying surface. The coating is also repairable. It can be sanded and reapplied for continuous protection.
• Smooth finish & improved quality – Applying a form coating can improve the overall quality of the casting. It creates a self-leveled surface that is flat enough to distribute the casting material evenly. The coated surface also ensures that the final precast product will have clean edges and smooth surfaces. Without the coating, there may be a rough, uneven texture on the surface of the cast piece. So, you’re not only lengthening the life of your form, but you’re also improving the aesthetics of the finished product.
• Easier casting removal – While a release agent is recommended before casting, the surface will be smooth and non-porous when the coating is applied. The casting mixture will not seep into the surface beneath the coating, which allows it to detach from the surface more easily. The easier release means less effort is required to remove the casting. The coating also prevents waste since the casting will come out intact, and the surface is undamaged for reuse.
• Versatility – A form coating epoxy is extremely versatile as it can be applied to a variety of surfaces using a roller. It bonds well to metal, wood, and foam. It should be able to contour to corners and edges no matter the shape or size of the form.
• Reduced maintenance – Because the epoxy is a smooth, non-porous material, it is easier to clean surfaces between castings. There’s no worry about debris, dust, or moisture slipping beneath and contaminating the form, which means faster turnaround times.

Types of Forms That Can Benefit

When deciding the type of material to use for your form or mold, there are a few things you should take into consideration. The surface material should be non-porous, non-reactive with the casting material, level, and rigid. A desirable form material would also be capable of accepting a coating that could reduce the adhesion between the surface and the casting material. Some common molding materials that could benefit from using a form coating include:

Metal

These forms are typically made of steel due to their reusability. They’re rigid, durable, and provide a smooth surface for casting. Simple, preformed metal surfaces make practical molds for casting. They will be more expensive than other materials due to their extended durability.

However, not covering the molding surface with a form coating epoxy can cause the metal to deteriorate faster than anticipated. Casting abrasive materials, like concrete, that contain alkalis directly onto a metal surface can cause corrosion. When the coating is used, it will prevent direct contact between the surface and the casting material. This barrier will protect the surface from developing imperfections that will affect the final cast quality.

Another reason a form coat epoxy should be applied to metal is so the casting material won’t bond to the surface and cause damage in the removal process. Because these forms are so expensive, it’s important to protect them for long-term use.

Wood/Sheet Goods

Wood and sheet good forms are the most basic and can be made of timber, plywood, particle board, or MDF. They will generally be simple, rectangular, and flat. Although these materials are easy to work with and cost-effective, they have a relatively short lifespan and won’t offer the same reusability as other materials.

Casting materials will stick more easily to an uncoated surface, which makes cured pieces difficult to remove. This adhesion can damage the surface, preventing the mold from being reused, and it will need to be repaired after each use. When a form coating epoxy is applied to a porous surface, it reduces the chance of adhesion or moisture absorption and increases the reusability of the form. If the surface absorbed some of the moisture from the cast material, it could cause it to swell and warp, leading to a poor cast. The absorption could also promote rot as the wood would absorb moisture and promote fungal growth.

The coating also, if necessary, can prevent the casting from copying the natural grain texture from the wood. When applied to the wood surface, it covers the texture and any imperfections, so the casting surface is smooth and non-textured.

EPS Foam

Foam forms are typically chosen for the ability to use a machine to create a specific shape without the additional labor of making them by hand. A machine-made foam part is used when a low-weight and highly precise mold is necessary. Since the foam is fairly delicate, it’s usually made for a single use or limited use based on the shape.

Solid blocks of foam can be carved to achieve a desired shape for casting. Foam pieces can also be glued together to create walls to pour casting materials into. However, the only way EPS is capable of being a casting surface is if a durable form coating is applied. The coating will make the foam more rigid and capable of withstanding abrasion and wear. This option also tends to have a lower cost than other materials because foam is inexpensive.

How to Prevent Form Failure from Occurring

Before pouring your casting material, prepare the surface to avoid issues. Certain factors can cause the form to fail. There are several ways to prevent that failure from occurring:

• Ensure adequate strength of the form – A strong form is essential to withstand the weight and abrasion of various casting materials, like concrete. Even the toughest surface will be prone to failure if you overfill the mold. That’s why a form coating is applied over the surface. It is rigid and takes on some stress during casting, so the surface is stable and reusable. Make sure the weight is distributed evenly, which can be done by vibrating the form. An adequate amount of coating will need to be applied based on the form material and thickness of the cast.
• Be cautious when using old materials – A form coating epoxy will wear over time due to the abrasion and wear caused by the casting material. The great thing about using one is that it can be reapplied. Look for signs of deterioration in the coating after each cast. If it’s time for a new application, sand the original coating and apply a new coat. It takes much less time to restore the coating than it would to replace an entire form.
• Don’t neglect maintenance – Conducting regular maintenance will prevent future failure due to deterioration of the coating. The coated surface should be cleaned after each casting is removed to maintain its integrity. Maintenance includes removing any casting residue before it is stored for future use. Ideally, you’ll want to store your forms indoors in a controlled environment.
• Take your time and be patient – Allow the concrete to cure properly before it is removed to prevent failure of the form. If you try to speed up the demolding process, you may end up with subpar castings or a damaged form.

If you want to protect your precast forms, contact VFI for information about our VFI-4385 82 D Form Coating Epoxy. We also have a polyurethane alternative: VFI-2538 70 D EPS Form Hard Coat.

Why Is My Urethane Rubber Mold Expanding?

Liquid urethane rubber molds shrink from low temperatures, but problems also arise if they are used in warm and humid climates. Pourable polyurethane rubber may expand in high temperatures due to its elastic properties. While these properties are beneficial, you must follow certain application procedures to ensure they work how they’re supposed to.

The dimensional stability of our urethane rubbers is tested using the ASTM D2566 method for thermoset casting systems. This is the percentage of linear shrinkage when subject to changes in temperature or humidity during cure. At room temperature, all VFI TDI urethane rubbers maintain dimensional stability below 0.001 in/in.

Once temperatures rise above 77°F, users may begin to see temporary expansion in their molds and forms due to weather.

Testing for Rubber Expansion

To prove that urethane expands when exposed to heat, we conducted a series of tests in our on-site lab. Using several samples of our own pourable urethane rubber and a few competitors’, we observed what happened when we adjusted the room temperature.

Once cast, cured, and demolded, we put the samples in an oven for 2 hours at 125°F. After the allotted time, we measured them and noticed they expanded by 1-3% on each side.

We then pulled the samples out of the oven and allowed them to sit for 2 hours at room temperature (77°F). We measured them again and noticed they returned to nearly the exact size of the molds they were cast in.

Results of our testing: If your mold or formliner has expanded due to a temperature change, it should return to its original size once it is brought back to room temperature.

Solutions

We’ve seen this kind of dimensional change occur when people work in warm, humid climates. If you plan to operate at a warm temperature, you’ll need to cast the mold in the same conditions. So, the liquid rubber and the environment temperature will have to be relatively the same as the temperature you plan to use the cured mold in. Also, as a note, please see our urethane shrinkage blog if you are using molds at a temperature that has dropped substantially from what it was molded at.

Urethane rubber must sit at room temperature for 16-24 hours before it can be demolded to prevent deformation. Keep the material at room temperature for an additional 3 days before use so it has time to gain strength and properties. The rubber will typically develop full physical properties after 7 days.

Casting the rubber against a rigid backing material can also prevent it from expanding due to high temperatures. We typically recommend using some type of wood, like plywood. Urethane’s high adhesion properties will form a strong bond with the surface.

We recommend pouring the urethane over the lip of the surface, allowing the material to grip onto it. When formed around and bonded to something more dimensionally stable, it won’t expand unless the substrate expands. Expansion or contraction of a sturdy substrate like plywood is very unlikely.

Contact VFI if you require further assistance with urethane rubber issues. We can also help you find the best material for manufactured stone, cast stone, and concrete stamps.

Understanding the Properties of Liquid Urethane Rubber

It is always essential to look at the properties of liquid urethane rubber when choosing a material for any project. If you’re new to urethane, you may not know what properties are most important to look at. The answer will vary based on what you plan to do with the material. This is a comprehensive guide to help you understand which ones are important to know and why.

What Physical Properties Are Important?

The physical properties of urethane molding rubber will tell you a lot about what the material is capable of. You’ll want to understand these properties to decide if the material you’re looking at is best for your project. These properties are tested using various methods from the American Society for Testing and Materials (ASTM). The most prominent physical properties listed for molding rubbers include the following:

Shore Hardness

Test method: ASTM D2240

Definition: Shore hardness uses a standard testing tool called a durometer to analyze a material’s resistance to localized deformation or indentation. The durometer determines the hardness of a material relative to materials with similar qualities on unitless scales.

Importance: This is one of the first properties users look at when determining if a material is suitable for their application. Hardness is a good indicator of properties, and generally speaking, the harder the material, the greater the properties.

Hardness factors into how easily a mold will demold from a model or casting. A softer material is much better when creating molds of delicate or detailed originals. Rubbers within the 20-40 A range are great for cast stone, while the 30-60 A range is great for manufactured stone. These types of applications use small and delicate original pieces that have the potential to break during the molding process, so softer molds will help demold more easily. Lower hardness is also recommended for architectural restoration projects as well.

Interested in reducing your product breakage rate? VFI has new polyurethane rubbers with release characteristics similar to silicone.

On the other hand, harder rubbers are better when you’re making large, flat, and simple molds. Their hardness makes them more abrasion resistant and capable of handling heavier loads, which helps lengthen the mold’s life. Rubbers within the 50-70 A range are great for detailed concrete formliners, while the 70-90 A range is great for simple formliners and concrete stamps. They also provide more strength so they can be used on casting beds.

Note: When looking at VFI urethane molding rubbers, you will notice that they all include the Shore hardness in their names to make it easier to find what you’re looking for (i.e., VFI-2143 45 A TDI Molding Rubber).

Tensile Strength

Test method: ASTM D412

Definition: Tensile strength uses a standard test to determine the maximum load or amount of stretching force a material can withstand before it breaks. The higher the tensile strength, the more force it can withstand. It is measured using pound-force per square inch (psi).

Importance: Tensile strength is one of the properties that tell you something about the durability of urethane. Generally, it will increase as hardness increases, but there are exceptions when custom formulas are created to achieve other higher properties at a lower hardness. With high tensile strength, the material can withstand loads, forces, and impacts without breaking or warping.

For mold making, the material should withstand the stretching forces exerted by the casting material. Having good strength is essential if you are making large molds that need to hold up to abrasive materials and large pours. Since urethane molds are meant to be reused, having good tensile strength allows them to endure repeated stress without failing. When demolding, the mold may be pulled, bent, and twisted to release the cast part, so this property helps it handle these forces and produce successful castings in high-volume production runs.

Elongation

Test method: ASTM D412

Definition: Elongation is tested to determine the maximum length a material can be stretched before it breaks. It is measured using a percentage of the final length compared to the original length of a tested material. It is also an inverse relationship with tensile strength as it uses the same test method.

Importance: While elongation isn’t a main concern for mold making, it’s still one of the physical properties users should know. If you require your molding material to have more stretch and flexibility, you’ll want to look at elongation. A mold with higher elongation will have a lower tensile strength, allowing you to demold from the master or the cast piece easier. Harder materials have lower elongation because they’re less flexible and have greater tensile strength, meaning they don’t have the same ability to stretch.

Tear Strength

Test method: ASTM D624 (Die C)

Definition: Tear strength, also called tear resistance, tests the maximum amount of force required to initiate a tear in the material. It is measured using pounds per linear inch (pli). Die C is the most common test type for urethane, and the test specimen is not nicked. The force acts parallel to the tab ends of the test specimen or at 45° to the 90° center.

Importance: Tear strength is considered one of the most important physical properties of urethane molding rubber. The reason for this is due to rough handling in the demold process. When removing castings from molds, tears or punctures can occur due to the pulling force when trying to break the tension between the mold and the cast part. Higher tear strength keeps the mold from tearing for easier part removal and a longer-lasting mold.

Tear strength is an important property and is loosely tied to the tensile strength of the material. Usually, the higher the tensile strength, the higher the tear strength. This means that when you have a high elongation, you will have a lower tear strength.

Dimensional Stability

Test method: ASTM D2566

Definition: Dimensional stability is tested to find a material’s ability to maintain its dimensions (size and shape) when it cures. It measures linear shrinkage expressed in inches per inch (in/in) between the cured material and the mold box or cavity it was molded from when cured at room temperature (77°F).

Importance: All two component urethane rubbers experience an exothermic reaction that generates heat as they cure, which causes the material to shrink. The degree to which this shrinkage occurs depends on the material, amount of exotherm, thickness, and geometry of the piece or mold. If more material is used to make large molds, you may notice a difference in the mold’s dimensions from the mold box or form it came from due to a larger exothermic reaction. This can also be an issue when casting thicker mold walls because it will generate more heat, leading to greater shrinkage.

If a mold material has good dimensional stability, it will retain its shape through the casting process. If the mold shrinks too much, cast pieces may be different sizes and may not fit together, especially in the case of manufactured stone.

Cast the rubber on a rigid backing material like wood to combat shrinkage when making larger molds. If you pour it around the lip of the backing material, it will create a better grip on the surface edge, making it harder for the material to shrink. Also, work at a consistent temperature so your environment doesn’t affect the material’s dimensional stability.

What Liquid Properties Are Important?

Not all companies split their properties into separate sections, but VFI specifies properties for urethane in a liquid state and when it is in its cured solid state. The following properties pertain to the unmixed and mixed liquid components:

Specific Volume

Definition: Specific volume is a property that relates to the volume of matter divided by the amount of matter or the reciprocal of its density to determine how much material is needed to occupy a given space. It is measured in inches cubed per pound (in3/lb). Simplified, this means that you can use the specific volume to determine the weight of product needed for your project.

Importance: Specific volume is an important property to know to calculate the amount of material you need to make a mold. First, the volumes (length x height x width) of your mold box and master must be calculated and subtracted from each other. Once you know the volume needed to fill the remaining space, you can divide it by the specific volume to convert it into weight. This number will be the total weight of urethane needed (Part A + Part B). Calculating this number ahead of time saves you from the risk of mixing extra material and generating waste or not having enough during the molding process.

Liquid Density

Definition: Liquid density is the weight of a material in a specified volume. It equals the mass of the liquid divided by its volume and is commonly measured in pounds per gallon (lb/gal).

Importance: Looking at a liquid density can tell you if there are useless fillers in the mix to increase the bulk and reduce costs. These fillers will notably change the weight of the material. As a standard, the liquid density of urethane rubber is around 8.5-9.5 pounds per gallon. If filler is included, you may see the liquid density range between 11-13 pounds per gallon.

Mix Ratio

Definition: The mix ratio is a property for liquid materials with several components that must be mixed to create a final product. It tells you how much of each part needs to go into the final mixture to produce the proper chemical reaction. It can appear in two ways:

• By volume: Mix ratio by volume is expressed as a ratio (Ex: 1A:1B) and is the exact proportions of Part A and B that must be combined and is not dependent on the weight. It is measured using equal-sized containers and is mostly used when processing through automated dispense equipment.
• By weight: Mix ratio by weight is expressed as a ratio (Ex: 51.50A:100B) and is the exact proportions of Part A and B that must be combined and is not dependent on volume. It is measured using an accurate scale, but if the user does not have one, selecting a material with a convenient mix ratio by volume is more desirable.

Importance: Most urethane rubbers are two-part systems (resin and hardener), and when mixed, they cure at room temperature. Staying on ratio for both parts ensures the material will cure successfully and achieve the desired properties.

If the mix ratio is not followed correctly, it can impact the final product. If you mix it with too little resin (B side), the material may become brittle. If you mix it with too little hardener, the material may become soft, tacky, or gooey to the touch. In some cases, not adhering to precise mix ratios can inhibit the cure, and the mold will never develop full physical properties, and it will be unusable.

Viscosity

Definition: Viscosity is the measure of a liquid’s resistance to flow. It will generally show up three times on a property sheet as Part A, Part B, and the mixed liquid viscosity. It is measured in centipoise (cps). For reference, below is a list of common household items and their viscosities so you are better equipped to understand the viscosity of urethane.

Importance: Urethane can come in a wide range of viscosities depending on processing needs, but pourable urethane will typically be between 200-3,000 cps. This property affects how easily the rubber can be mixed and poured into a mold. Less viscous rubber is easier to mix and pour, especially when using more complex molds. It will flow more readily into details, corners, and pockets. Rubbers with a lower viscosity are also less likely to trap air bubbles in the finished molds.

On the other hand, high viscosity materials are thicker and have a greater resistance to flow. There is a higher chance that the rubber will cure with air bubbles that create imperfections on a mold’s surface. A great way to combat air bubbles in thicker rubbers is to vacuum degas the material before pouring.

Having material components with similar viscosities that must be combined is also important to maintain a uniform mix. This varies when trying to incorporate a thinner material into a much thicker material because it requires a longer mixing time than if they had similar viscosities.

Pot Life/Work Time

Definition: Pot life or work time refers to the time it takes for the material to reach a viscosity where it is deemed too difficult to work with. For molding rubber, it is essentially the time after you start mixing that the material is pourable.

Importance: Understanding a material’s pot life is essential for having control and flexibility in the mold making process. It will tell you exactly how much time you have to mix, vacuum degas, and pour the material into a mold.

Depending on certain working conditions, the pot life may be shortened. Temperature is the number one factor that affects this. If the material, the environment, or the mold temperature is increased, pot life will decrease. It’s important to work at room temperature (77°F) or cooler temperatures. However, working in warmer temperatures will have the benefit of reducing the cure time if you need to process your molds faster.

The amount of material you use at one time can also affect the pot life. When you use more material, the extra mass causes more heat to be generated through the exothermic reaction. This heat then causes the rubber to become more viscous quicker. Heat is also a problem for thick-walled molds. More material concentrated in one area will cure much faster than thin sections.

Pot life is even more important if you’re making large molds or form liners. You’ll want to find a material with a long enough pot life that will allow you to mix and pour into the mold before it starts to solidify. Most urethane users will use dispensing equipment for this exact reason.

Demold Time

Definition: Demold time indicates the amount of time a material should cure before being removed from a mold, mold box, or form. Depending on the cure speed of the material, it can vary from minutes to hours.

Importance: You must wait until the material has solidified enough before demolding; otherwise, it may cause distortion or deformation. All cure times are based on room temperature (77°F) unless otherwise stated, and temperature will play a major role in demolding. The mold can be left in an area warmer than room temperature to speed up its demold time.

When the mold is removed from the mold box or form, it does not mean that it is ready for use. Polyurethane rubbers need up to 7 days to obtain final physical properties; however, they can be used for casting about 72 hours after they have sat at room temperature. Using the mold before this time can also result in deformation from casting pressure or increased difficulty when demolding.

Place Into Service

Definition: Place into service is the amount of time before a material is ready for use. It is measured in hours or days.

Importance: Not every manufacturer lists the place into service time for their urethane materials. However, it is a good property to know because it provides a time frame for when you can start using the mold for casting.
Urethane can usually take several days to develop desired properties, so a newly made mold can’t be used right after its initial cure. After sitting outside of a mold box or form at room temperature for a few extra days (72 hours minimum), the mold should have enough properties for casting.

Where to Find Material Properties?

Volatile Free, Inc. and most manufacturers list physical and liquid properties on product pages and technical data sheets or bulletins. We know the value of expressing these material properties accurately, so you can trust that the product you’re using will perform to specification. We use various standard ASTM test methods to determine a product’s properties and only publish them once they have gone through multiple reviews. Technical data sheets can be found on any product page under the resources tab.

How to Seal Styrofoam for Outdoor Use

There are several ways to seal styrofoam for outdoor use. You should prioritize weather-resistant materials to seal the foam, ensuring the longevity of your piece. Whether it’s rain, sun, impact, or other outdoor factors, styrofoam requires extra protection to maintain its structural integrity, especially if it will be placed in storefronts, public spaces, or outdoor events.

Protection is important, not just for styrofoam, but other foams too. Most foam sculptors in the industry are actually using expanded polystyrene (EPS) over styrofoam (the brand name for extruded polystyrene (XPS)). This is because EPS is made in large blocks, and XPS is made in sheets.

Regardless of which styrene foam you use, both are inexpensive and easy to work with but can become damaged if not protected with a durable hard shell.

Does Foam Last Outside?

Styrene foam is not designed to withstand extended outdoor conditions. One reason foam should be sealed is because it is highly sensitive to UV rays. The plastic material will break down into a discolored powdery substance or become brittle upon long-term exposure. It can fully break down in a few years, which is bad for the environment if not disposed of properly.

In addition to this degradation, excessively heating the material can break down its chemical structure, causing it to leach. Small amounts of styrene will seep out and contaminate surrounding surfaces, which means if your foam piece is within reach of people, it’s not safe. The foam may also lose its thickness during this process.

While it is water resistant, it’s not waterproof. Over time, it will absorb moisture from rain, snow, or spills. Extra water may also be stored causing mold and mildew growth. In addition, there are also a handful of solvents that can melt or break down polystyrene . Impacts from various environmental conditions can also damage uncovered foam. If you want to protect it from damage, it is crucial to apply some sort of coating or sealant.

Options for Sealing Styrofoam

When you seal styrofoam for outdoor use, the material you choose will depend on how long you need the piece protected. While many people use DIY methods because they’re more cost-effective, there are specialized hard coats for styrofoam that lengthen the life of your project.

Polyurethane is the top suggestion for sealing styrofoam. These coatings are two component, semi-rigid materials that are plastic-like and impact resistant when they harden. When applied, they provide the durability and flexibility needed to protect the surface underneath without cracking. Most are applied by high pressure spray equipment, but there are also brushable options, such as VFI-2519 75 D Brushable Hard Coat, for smaller projects. For lower cost spray options, there are even coatings in a cartridge format, such as VFI-6171 70 D Qwik Spray Hard Coat.

Polyurea coatings are a similar alternative but come with premium properties at a lower hardness in comparison. These properties will make the cost slightly higher, but they do offer more in the way of protection in the form of impact and thermocycling. They are usually fast setting and they’re also a great alternative if you work in environments where moisture is an issue. One downside to a polyurea material is that it is normally harder to sand, because they tend to be softer than a urethane hardcoat.

Epoxy is a coating with similar characteristics to polyurethane and polyurea. It acts as a protective barrier for any type of foam but is applied in several thinner coats. Epoxy is also mostly brush-applied or roll-applied, which makes it time-consuming to work with, so it’s typically used for smaller projects. If you plan to sand the material, particles get into the air and can create toxic dust, so an approved respirator should always be used. The main benefit is the ability to work on large projects without the need for a full spray booth.

Fiberglass has a more time-intensive application process, but it is an effective way to protect an outdoor foam piece. Layers of the material are placed over the foam with intermittent applications of epoxy or polyester resin that will impregnate the fiberglass fabric/fibers. These layers are applied until the desired thickness is achieved providing strong impact resistance that is reinforced by layers of fabric. Resins that are not a full 100% solids will melt the foam, so you must be careful in choosing the right one.

Benefits of Sealing Styrofoam for Outdoor Use

• Protection – There are several things a hard coating can protect outdoor styrofoam projects from. The coatings resist moisture and water damage, UV radiation (when a compatible paint or topcoat is applied), and other weather conditions. They also resist impact and abrasion from people sitting on, climbing up, or touching these structures. Some coatings can also provide fire retardant characteristics to meet fire safety requirements where necessary.
• Long-term durability – Because a coating can offer incredible protection, it keeps your foam piece in good condition, especially outside. If you were to just paint your foam piece and call it a day, there’s no doubt that it would deteriorate quickly and not look very smooth. When your project is resistant to external factors, it lasts longer and saves you money in the long run.
• Versatility – There’s no limit to the shapes and projects you can use a hard coat for. Because spray coatings are the most used and recommended application option, the coating gets into all the curves and crevices on a piece. These coatings adhere well to all types of foams, so you gain protection no matter what material you use.
• Easy to apply & work with – Most hard coatings are relatively easy to work with, as long as you have experience with high pressure spray equipment. Most formulas also come in 1:1 mix ratios for ease of setup. If spraying is not your thing, brush and roller applications are also available. After application, coatings are easy to post work. Fast setting coatings can leave a smooth surface perfect for top coating or painting, especially when spray applied.

Outdoor Applications for Sealed Styrofoam

Due to the adaptability of sealed foam, a handful of outdoor applications benefit by using these materials. These materials are used to fabricate signs for outdoor store displays, theme park rides, restaurants, and more to enhance brand recognition and draw customers in. Nothing elevates an aesthetic like a custom sign that stands out from less creative materials.

Companies may also use foam to create large-scale 3D figures or characters to attract visitors and create magical environments. They can be seen at outdoor festivals, concerts, parks, gardens, etc. With a hard coat, your creations will be protected for years.

Sometimes, these materials are used for realistic outdoor hardscaping, such as stones, edging, boulders, rocks, and more. Foam hardscape objects can be more cost-effective since natural materials are more expensive and difficult to install. Heavy machinery is typically not required when installing hard-coated foam pieces, reducing labor costs.

Outdoor amusement parks rely heavily on custom props to immerse customers and enhance their experience. Hardened foam can be used as themed elements in ride queues, in the rides themselves, or throughout the park. The protection these hard coats offer keeps your projects in good shape for a long time.

Contact VFI today to see if you could benefit from using a hard coat on your next foam project.

How to Use a Form Coat Epoxy

Learning how to use a form coat epoxy is important for generating multiple quality castings when using abrasive casting materials. Creating a stable surface to pour concrete will help control and shape it as it cures. These qualities help ensure that the material will set properly and maintain its strength, durability, and longevity when transported and installed at building sites.

However, bare wood, foam, and metal surfaces will not last long without a form coating, so it’s crucial to protect your investment with a strong barrier. Using an appropriate coating will ensure that the surface can withstand the weight of rough casting materials for multiple uses without becoming damaged.

What Is a Form Coat Epoxy?

Form coat epoxies are also called mold coats or bed coats in the precast industry. This is due to their versatility, as they are used to protect large formwork, casting beds, or molds for precast, tilt-up, slip form, and cast-in-place applications. The castings produced from these forms include beams, columns, walls, etc., made of cementitious materials.

A form coating creates a tough, rigid surface that adheres well to wood, steel, and even EPS foam. It acts as a barrier to protect these expensive molding forms from the abrasive effects of various casting materials. The coating will act as a shell over the surface to prevent it from absorbing the casting material, which would otherwise have a hard time releasing from the form or surface. The smooth coated surface is then used to create multiple identical and flat building materials for parking structures, bridges, highway walls, retail shopping centers, and more.

Specially formulated epoxy coatings work well for this application. They are rigid but are formulated to also have the flexibility to resist cracking or deforming from regular use. Because these coatings have outstanding properties that make them strong, they become almost unbreakable, reducing the risk of damage to the underlying surface. Epoxy coatings require minimal maintenance and will endure heavy wear and tear before they need to be recoated.

Importance of Surface Preparation

For excellent adhesion to the following surfaces, you must ensure they are free of dirt, debris, and other foreign materials.

• Wood forms – Sand new wood panels for good mechanical adhesion of the coating. Clean off the sawdust with a vacuum. Though the coating is moisture insensitive, ensure the surface is relatively dry before application.
• Steel forms – If the metal contains rust, mill scale, dirt, and other contaminants, you will want to conduct abrasive blast preparation by sandblasting to SP6. Once finished, clean the metal shavings off the surface with a vacuum or broom.
• EPS forms – While EPS is typically not used for large-scale production, it can be used for casting smaller pieces. The foam must be aged at least 30 days to allow any gas to escape. The higher the density of the foam, the nicer the finish, but any foam between 1-3 PCF is acceptable. The foam should be clean and dry before applying the coating. The coating will not deform the mold shape.

The Form Coating Epoxy Application Process

Materials needed: VFI-4385 82 D Form Coating Epoxy, nap roller, wet film thickness mil gauge, large industrial orbital or rotary sander

Because epoxy can be toxic when inhaled, swallowed, or in contact with skin, use the material in a well-ventilated area. Wear the necessary personal protective equipment (PPE) to avoid exposure.

It is always recommended to work with the material at temperatures between 60-80°F. Remember, you will have a shorter working time when the temperature is higher. After preparing your casting surface, follow the steps below to create a protective barrier on your molding surfaces.

• Once you have mixed the components together, pour the material onto the surface.
  • Note: Leaving it in a mixing container can cause it to over-generate heat, which causes the material to thicken faster and cure faster. Do not leave material in a mass to cure. Mix up only what is needed to prevent excess.
• Begin rolling the material evenly at a rate of about 20 mil passes. It can be back-rolled to help achieve a uniform thickness. Coverage will vary in the first application due to the porosity of the surface.
• Check the thickness with a wet film thickness mil gauge. The coating should self-level.
• Allow it to cure overnight (minimum of 16 hours).
• Once cured, power sand the surface to smooth out imperfections or bubbles. Clean the surface of dust and debris from sanding.
• Apply a second coat following the same instructions. Repeat the process until the overall desired thickness is achieved.
  • Note: Total thickness should not be thicker than 250 mils.
• Before casting, spray a release agent to prevent unwanted adhesion between the form coat and casting material.
• Pour the casting material into the coated form and allow it to harden until it can be removed, typically after 24 hours. The surface can then be reused for future castings if the surface is clean, free of dust, and dry.

Once the original form coat becomes worn, a new coat can be applied. All you need to do is sand down the existing coating to remove any previous casting residue and improve surface adhesion for the new coat.

VFI Compatible Products

VFI-4385 82 D Form Coating Epoxy is VFI’s exclusive product for precast manufacturing purposes. It has a convenient 2A:1B by volume mix ratio for easy application with a roller. It is moisture-insensitive, so it can be applied to damp surfaces with no effect. At 82 D Shore hardness, the cured coating will produce a highly rigid yet flexible surface perfect for repeated concrete casting. Contact VFI if you are interested in protecting your wood, steel, or foam surfaces.