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:

Material	Viscosity
Water	1-5 cps
Blood	10 cps
Corn syrup	50-100 cps
Maple syrup	150-200 cps
Castor oil	250-500 cps
Honey	2000-3000 cps
Molasses	5000-10000 cps
Chocolate syrup	10000-25000 cps

 

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.