VFI®-5208 8 PCF Semi-Flexible Polyurethane Foam

VFI®-5208 8 PCF Semi-Flexible Polyurethane Foam

VFI-5208 8 PCF Semi-Flexible Polyurethane Foam is a two-component, water-blown urethane foam that is compressible with good bounce back. The 8 pounds per cubic foot expanding foam has a slow enough gel time to be machine-injected or hand-poured into a mold or form. Its self-skinning capabilities allow it to create a smooth, uniform surface for an improved appearance. With the ability to overpack, this semi-flexible foam is formulated to fill cavities and prevent voids. VFI-5208 is capable of creating many different parts and shapes for prototyping, form liners, manufactured stone, precast, and more.

VFI-5208 8 PCF Semi-Flexible Polyurethane Foam from VFI is a water-blown, self-skinning foam that can be poured or injected to make many parts and shapes.

Features & Benefits

  • Great rebound and strength allow the foam to hold its shape
  • Works as a backfill material to adjust the weight of a piece
  • Self-skinning capabilities create a surface that can be primed or coated
  • Convenient 1A:2B mix ratio by volume for quick and easy application
  • Fast final cure speed for a quick turnaround on parts

Instructions for Use:

Mold Preparation

Porous materials such as natural stone, wood, and concrete must be sealed and released to prevent unwanted adhesion. Molds must be dry and coated with a release agent to extend the life of the mold. The mold must be strong enough to hold shape if subject to packing pressure. For better results, you can use a heated mold up to 120°F to speed up the demold time. However, heating the mold will also decrease the pot life and final density. Compatible molds for casting include metal, urethane, epoxy, and platinum silicone.

Mixing, Pouring, & Curing

The material should be brought to a minimum temperature of 65°F before use. Premix the B side (Poly) until uniform before combining with the A side (Iso). Pour the measured B side into the measured A side and mix rapidly with a drill or power mixer. Move the mixer through the center until uniform. Transfer the mixture to a new container and mix again before use. The material must be completely mixed before the 30-second cream time (initial rise).

The material should be poured immediately into the lowest point of the mold or form. Allow space for the foam to expand. Avoid scraping material from the container while pouring, as this takes time, and the material may not be fully mixed.

Once poured, the mold should not be moved while the foam rises since movement could cause cells to collapse. To prevent deformation, allow the foam to remain in the mold or form until fully cured. VFI-5208 should be allowed to cure for at least 2 hours at room temperature before removing it from the mold. Thinner pours may require a longer cure time.

Cleanup

Clean application equipment with MEK or xylene before the foam cures. If the foam has cured, you can break it off the surface and wipe the rest off with xylene.

Safety

*Always read the safety data sheet before working with chemicals  

Use chemicals only as directed and for their intended purpose. Do not dispose of chemicals down the drain. Most chemicals must be disposed of as hazardous waste.

PPE to avoid all unnecessary exposure:

  • Eye protection – wear tightly fitted chemical safety goggles or glasses. Wear a face shield if a splashing hazard exists.
  • Hand protection – wear chemical-resistant protective gloves to prevent all skin contact. Suitable materials may include chloroprene rubber (Neoprene), nitrile rubber (Buna-N), chlorinated polyethylene, polyvinyl chloride (Pylox), and butyl rubber, depending on the conditions of use.
  • Body protection – wear suitable protective clothing. Cover as much exposed skin as possible to prevent all skin contact. Suitable materials may include saran-coated material
  • Respiratory protection – In case of insufficient ventilation, wear suitable respiratory equipment. Respirator selection must be based on known or anticipated exposure levels, the hazards of the product, and the safe working limits of the selected respirator

Product Limitations

VFI-5208 contains isocyanate, which can be irritating to the skin and toxic if inhaled as particulate matter. Avoid prolonged breathing of vapors and repeated skin contact. It must be protected from freezing. It is not UV color stable and has no long-term UV testing. If needed for exterior use, the foam must be painted or sealed. It is not fire retardant and is unstable in water.

  • Incompatible materials – A side: acids, amines, alcohols, water, alkalines, strong bases, and substances or products that react with isocyanates. B side: none known
  • Conditions to avoid – A side: moisture and freezing. B side: heat and incompatible materials
  • Chemical stability – the product is stable if stored and handled as prescribed/indicated
  • Reactivity – A side: no corrosive effect on metal. Based on its structural properties, the product is not classified as oxidizing. B side: No dangerous reaction known under conditions of normal use
  • Possibility of hazardous reactions – A side: Reacts with alcohols, acids, alkalis, amines, and water with formation of carbon dioxide. Risk of bursting, exothermic reaction, and polymerization. Contact with certain rubbers and plastics can cause brittleness of the substance/product with subsequent loss in strength. B side: No dangerous reaction known under normal use
  • Hazardous decomposition products – A side: carbon monoxide, carbon dioxide, nitrogen oxides, hydrogen cyanide, aromatic isocyanates, gases/vapors. B side: may include, and are not limited to, oxides of carbon

Potential Health Hazards

  • May cause respiratory tract irritation. A side material may also cause allergy and asthma symptoms or breathing difficulties if inhaled.
  • Causes skin irritation or sensitization: redness, edema, drying, defatting, and cracking of the skin.
  • Causes serious eye irritation: discomfort, pain, excess blinking and tear production, marked redness, and swelling of the conjunctiva.
  • May cause stomach distress, nausea, or vomiting if swallowed.

*If you are experiencing any of these symptoms, seek medical advice or attention. Call a poison control center or doctor if swallowed.

Application Methods:

  • Inject Inject
  • Pour Pour

Available Packaging:

  • Tote
  • Drum
  • 5 Gallon
  • 1 Gallon

Frequently Asked Questions

Why isn’t my urethane rubber mold curing?

There are a few reasons urethane rubber might not cure. If you’re seeing spots or streaks of uncured material, it’s likely that the material wasn’t thoroughly mixed before it was poured. The best way to ensure your material is fully mixed is by using a double-mix method. Once your components are measured by weight or volume, combine them in one bucket and mix. Before pouring into your mold box, pour the material into another container and mix again. This reduces the likelihood of seeing these streaks or spots of uncured material.

Another reason urethane rubber might not cure is due to an off-ratio mix. It is essential to follow the mix ratio of each material precisely, whether using volume or weight. These ratios are what help the material cure. If the mix ratio is not followed, it can result in a sticky, unusable mess.

One last thing to note is temperature. If your work environment, model, or material is too cold, the material will have a hard time curing. Urethane rubber is a room-temperature curing material, so we generally recommend using the material at 77°F for the best results.

How can I minimize air bubbles in my mold?

To combat trapped air, you’ll want to work in a temperature-controlled environment. Also, mix the material slowly and pour it into the lowest part of the mold box, allowing the material to spread naturally as you pour. It is also important to give air a way to release when doing molds that are not open backed molds or have severe incuts.

Why am I seeing bubbles and pinholes on my urethane mold?

Bubbles usually indicate that there is trapped air in the mix. One reason bubbles form on the rubber’s surface is due to moisture. Urethane is moisture sensitive and may have reacted with moisture within the mold box or environment. Moisture can come from humidity, a wet or porous model, or wet mixing containers and sticks.

Another reason air bubbles may have formed could be from using too much mold release. While it’s important to use release to ensure the material will demold from the molding surface, using too much will affect the cured surface as well.

What is your price?

VFI strives to offer competitive prices for our molding rubbers, but it will ultimately depend on a handful of factors, including the availability of raw materials, the raw materials used in the formula, and the properties of the final product. We also pride ourselves on manufacturing our own products, which keeps the price down and gives us full control of the manufacturing process.

Do you sell to other concrete companies?

We have a vast customer base in the concrete industry of manufacturers who use our urethane rubber for precast panels, manufactured stone, cast stone, architectural restoration, hardscape, décor, and more. There’s no limit to what kind of concrete castings you can make with these materials.

How long have you been in business?

VFI has been manufacturing high performance thermoset polymers for almost 30 years. While our origins were a little different to what we currently do, we have always been in the molding material market for industrial applications.

Does your product work?

VFI prides itself on only offering materials that have been thoroughly tested using standard ASTM methods. We have determined through feedback from our customers that our urethane rubbers work in a similar capacity, if not better, than our competitors. Our rubbers are preferred because they are MOCA-free with low-moisture sensitivity, low exothermic reactions, and longer lifespans.

VFI is also an innovator in the concrete casting industry and has created urethane rubbers with release characteristics similar to silicone, which have produced breakage rates as low as 2-3%.

Can you make your urethane in any other colors?

VFI’s TDI-based urethane rubbers come in two distinct colors: blue and neutral. If you want to add color to the neutral version, urethane pigments can be purchased and added to the B side (Poly) material before mixing with the A side (Iso). No water-based pigments should be used.

How should I store my urethane rubber mold?

Clean the mold before you plan to store it. We recommend storing them indoors where there is no chance of UV exposure. The environment should be clean, dry, and temperature-controlled. Also, make sure the mold is stored flat as this will help it from permanently distorting in storage.

Can I store my molds outside? In sunlight?

Do not store your molds outdoors or in direct sunlight. Outdoor conditions can cause the mold to deteriorate before its typical lifespan. UV rays will also change the color of the mold and can cause chalking. Store the mold in a cool, dry environment, out of direct sunlight, where temperature is controlled.

How should I clean my urethane rubber molds?

Urethane molds can be wiped down with soap and water before they are used again or stored for future use.

How often should I use mold release during the casting process?

Because urethane will adhere to anything, apply release after each casting. The release will have worn away during the demolding process, so it’s important to reapply and negate that adhesion. Allow the release to dry before pouring the urethane on top.

How many pulls can I get out of a urethane rubber mold?

The amount of pulls you can get from VFI urethane rubber depends on the properties, what you’re using it for, and how you take care of it. To prolong the life of the mold, you’ll need to use adequate release after each cast so as not to damage the mold or casting. When you store the mold when it’s not in use, you’ll want to keep it in a clean, room temperature-controlled environment. Choosing the proper hardness will also lengthen the life of the mold.

How soon can I use the mold after demolding it? (How long does it need to cure?)

Most VFI molding rubbers must sit for a minimum of 16 hours at room temperature (77°F) before they can be demolded. After demolding, they must sit for another 3 days outside of the mold to develop the necessary green strength for molding purposes. Even though the mold can be used after 3 days, keep in mind that the material requires 7 days to develop full physical properties. Note: during the 3 days, fully support your mold to prevent it from forming into an unwanted shape.

How long until I can no longer repour the material?

Customers who pour large molds will need to pour several batches of rubber to create the thickness needed for a strong mold. As a standard for our molding rubbers with longer pot lives, you will only be able to pour additional rubber up to 4 hours after the initial pour. Staying within the repour window will allow the rubber layers to bond efficiently.

What temperature should I pour the rubber at?

VFI always recommends pouring in the same conditions you will be using the cured product. If you expect to work in warm conditions, pour the rubber in an environment at similar temperatures. The process is the same if you anticipate that you’ll be using the cured product in cold temperatures. The rubber should then be cast in cool temperatures. This will prevent unwanted shrinkage or expansion of the mold that could compromise the casting process. Note: the cure will be affected depending on the temperature that you pour at.

Why is my urethane rubber mold expanding?

If you cast in a really cold environment and then use the mold in a very warm environment, you might notice your mold temporarily expand. You must cast the material in the same conditions you will be using it in when it has cured. We recommend casting against a rigid backing material so the rubber can grip onto it to prevent expansion from occurring further.

Why is my urethane rubber mold shrinking?

If you cast in a really warm environment and then use the mold in a very cold environment, you might notice your mold temporarily shrink. You must cast the material in the same conditions you will be using it in when it has cured. We recommend casting against a rigid backing material so the rubber can grip onto it to prevent shrinkage from occurring further.

Does temperature affect the mold making process?

Yes, the temperature of the environment, material, and models affects liquid urethane when making molds. If the temperature is too cold, it can slow down the pot life and curing process, and if the temperature is very high, it can speed up the pot life and curing process. If it is cold enough, the material may not cure at all. We recommend using urethane rubber at room temperature (77°F).

How do you mix the molding rubber?

VFI recommends a specific double-mix method for mixing our urethane molding rubber. First, you will determine how much material you need and measure that out using the mix ratio by volume or weight. Once you have the A side in one container and the B side in another, thoroughly premix the B side and then combine it with the A side. Mix them until uniform using power mixing or meter mixing equipment. Be sure to scrape the bottom and sides of the container for uniformity. Transfer the material to a new, clean mixing container and mix again. This will ensure a thorough mix before it is poured into the mold box.

Should I measure by weight or volume?

Whether you should pour by weight or volume depends on your unique molding process. If you pour rubber in smaller quantities, either method works. To measure your material by weight, you will need an accurate scale. Since most of our liquid urethane rubbers are 1A:1B by volume, some users find it easier to measure their material that way. If you have a proportioner that automatically mixes large quantities of your material when needed, following the mix ratio by volume is usually the way to go.

Should I use silicone or acrylic caulk to seal my mold box?

When sealing your mold box, you should use acrylic caulk because silicone can inhibit the cure of urethane.

How do I prepare the mold box and model before pouring urethane rubber?

All edges of the mold box must be sealed as well as the edges of your models, so the molding rubber is not able to seep out of the box or underneath the models. To seal the edges, you can use a sulfur-free clay or acrylic caulk. See answer #5 for information about sealing and releasing the molding surface before pouring the urethane.

What happens if I use too much release?

Using too much release may affect the surface of your castings. The surface may have a shiny or gloss-like appearance, which may not be desirable for your application. We recommend spraying light mists of release over your molding surface and allowing it to dry before casting.

Can I use an oil-based release with urethane rubber?

Do not use an oil-based or biodegradable concrete release like soy bean form oil when molding with urethane. These materials can cause your mold to continuously expand as you apply the release.

Do I need a release agent? What kind?

Non-porous surface to urethane: When working with urethane rubber, you must use a release agent to prevent the material from bonding with the casting surface. VFI has had great success using Chem-Trend MR-515 Aerosol with our urethane molding rubbers. You can also utilize a similar silicone-based release agent.

Porous surface to urethane: When working with a porous surface, it must be properly sealed before you begin pouring the molding rubber. VFI recommends creating a mixture of 80% mineral spirits to 20% petroleum jelly by weight to seal the surfaces. After applying several layers with a chip brush, spray a light mist of an aerosol release agent over the entire surface. VFI recommends Chem-Trend MR-515 Aerosol or a similar silicone-based release agent.

Concrete or stone to urethane: When casting concrete into a urethane rubber mold, VFI recommends utilizing one of Chem-Trend’s water-based releases specially designed for releasing concrete from urethane. For example, the CR-19597 is ready to use and can be diluted.

Also, VFI recently released a new series of Max Release Molding Rubbers that enhance the releasing characteristics for sensitive projects. Check out our press release for more information.

What kind of clay works best with urethane rubber?

When making a mold, use clay to seal the mold box walls and models so the liquid material cannot slip through or underneath. When using urethane rubber, you’ll want to use a non-hardening, sulfur-free clay to prevent unwanted adhesion or cure inhibition. Do not use water-based sulfurous clay, as urethane is extremely moisture-sensitive and will stick to the clay once it is cured.

How thick should my mold walls be?

Pour thickness will depend on the hardness of the rubber chosen. Because softer rubbers are more flexible, they’re more prone to tearing. Generally, the softer the rubber, the thicker your mold walls should be, and vice versa. For example, VFI-2123 is a 25 Shore A rubber and should be poured at a minimum of 1 inch thick. On the other hand, VFI-2180 is an 80 Shore A rubber and can be poured at a minimum of 3/8 of an inch thick. Check out VFI’s TDI specification sheet for recommended pour thickness minimums.

How much urethane rubber do I need to make a mold?

To determine how much mold rubber you need, you’ll first need to calculate the cubic volume (formula: length x width x height) of your mold box and models. Once you have those volumes, you’ll subtract the model volumes from the mold box volume. This will be the remaining space in the mold box that needs to be filled.

All VFI’s molding rubbers list specific volumes on each technical data sheet (TDS), so once you find that number, divide your volume by it to convert it into weight (formula: volume / specific volume = total weight (A side + B side)). Always weigh up more product than you might need to account for loss in the container or for any math errors.

What durometer of rubber do you think I need?

The best durometer for your project will depend on your unique project requirements. For cast stone applications, we recommend using one of our 25-40 A rubbers. For manufactured stone applications, we recommend using one of our 30-60 A rubbers. For advanced detail formliners, we recommend using one of our 50-70 A molding rubbers. For simple formliners and stamps, we recommend using one of our 60-90 A molding rubbers. Projects that require extreme detail, such as architectural restoration, will want to use a lower durometer rubber. Projects that require a large amount of rubber to hold heavy, abrasive casting material will want a harder rubber that can withstand the weight.