Effects of Temperature on Polyurea, Urethane, & Hybrid Spray Coatings

Temperature has a big influence on the performance of protective spray coatings, like polyureas, urethanes, and hybrids, across every type of application. Most coatings are sensitive to temperature, and not every one is suitable for all weather.

If you are not aware of the recommended service temperatures when applying a coating, you may experience failures and inadequate protection of the surface.

If you apply coatings below the optimal range, you may experience slow curing, sagging, and poor adhesion. If you apply them above the optimal range, they will dry faster. This can lead to uneven application and limited final properties.

This guide will delve into what protective coatings are and why temperature is important for proper application.

What Are Protective Coatings?

Protective coatings are used in various settings when a surface needs to be shielded from damaging elements. These elements include daily wear, weather conditions, corrosion, chemical attacks, impacts, and abrasion. Their main goal is to extend the life of the surface to which they are applied. A secondary goal may be to provide a smooth, uniform surface for aesthetic purposes.

Types of Protective Coatings

• Polyurea is referred to as a premium coating on the market. It offers outstanding properties and the fastest cure times. It is moisture-insensitive, which can be beneficial in certain environments. It’s been used for secondary containment, kennel floors, sacrificial applications, and more.
• A subset of polyurea coatings is polyurea hybrids. They are a blend of polyurea and polyurethane, which makes them lower in cost but more sensitive to moisture. Depending on the application, these coatings can be the most desirable option. They are used as protection for a handful of vehicles and parts (truck beds, work trucks, recreational vehicles, trailers, etc.), tank pads, speaker boxes, etc.
• Polyurethane is popular in the theming industry as it can be formulated as a hard coating to protect EPS structures. Urethanes have great properties for indoor and outdoor protection. They’ve been used on architectural shapes, custom signs, props, and full themed environments. However, they are more sensitive to moisture than the alternatives.

What Temperatures Affect Coatings?

• Ambient Temperature. This is the temperature of your working environment. If you are spraying outdoors, this temperature is much harder to control. Outdoor projects are done when the weather permits. Humidity is an aspect related to temperature that can affect the coating. High moisture content in the air is not desirable when applying these materials, especially urethanes.
• Surface Temperature. This temperature is not talked about as much as ambient, but it is important to know for proper application. The surface temperature may be different from the air temperature. It can affect how the coating behaves and cures. Extreme temperatures can lead to poor curing and reduced longevity. Warm surfaces can also cause moisture to form. This moisture can get trapped between the surface and the coating, causing adhesion issues and surface defects.
• Material Temperature. When stored, the material will reflect the temperature of the environment. So, if the material isn’t stored at consistent temperatures, it might affect the overall coating application. Many coatings come in two parts and produce a chemical reaction when combined that causes them to heat up while they cure. However, if the material temperature is too low from storage, it may affect the cure.

What Properties Does Temperature Affect?

Knowing how temperature affects coating properties will help with successful and long-term performance.

Properties are determined based on tests at room temperature (77°F) and low relative humidity. They will vary if conditions are above or below this standard. Colder temperatures will cause more issues for coatings than warmer ones.

Gel time

If the temperature during application increases by as much as 15°F, you can expect the gel time to be reduced. This gives you less time to work with the material. When these materials are sprayed, they’re already fast-setting, so time is limited even further. Working past the gel time can affect adhesion, durability, and texture from additional overspray, resulting in a rougher finish or coating failure. Having to rework or recoat due to a shortened gel time can be expensive and time-consuming.

If the temperature decreases by 15°F, anticipate an extended gel time. Having extended time to work with the material may be desirable. However, this can lead to project delays since the coating will take longer to cure, not cure properly, and be hard to texture.

Maintaining temperature will ensure the gel time is consistent and maximize coating performance. It also helps reduce waste and downtime, and keeps your project on track.

Viscosity

Viscosity determines how thick a coating is and how easy it is to apply. A desirable viscosity allows consistent application, a uniform finish, and optimal performance. Different application methods require different viscosities. Lower viscosity is desirable for even distribution and fine atomization when spraying.

If you can’t control temperature, you can’t control viscosity. Warm conditions make the coating thin and easy to work with. Extremely warm conditions can make the coating too thin, which makes it harder to control. This may result in sagging, uneven layers, increased self-texturizing, and inadequate thickness. This may result in an orange peel texture or streaks.

Cool conditions make the coating thicker and harder to apply. In extremely cold conditions, the coating may not flow well. A thicker coating might also have difficulty wetting out the surface and adhering.

Note: Humidity may affect the coating, depending on the formula. Thinner coatings are better at releasing trapped air or moisture. So, if the coating is thick, it may have a harder time releasing bubbles.

Cure Time (Dry to Touch)

Cure time is the process that allows the material to achieve its initial strength and properties. Pot life and cure time are intertwined with each other and temperature. If the pot life decreases due to higher temperatures, so will the cure time. If the pot life increases at lower temperatures, the cure time will too. Many coatings have to remain at a certain temperature to cure.

Cold temperatures can slow or even inhibit the curing process. While an extended pot life can benefit larger coating projects, it can also cause delays and increase costs. The coating is delayed in developing strength and may remain soft, weak, and susceptible to damage. It can also result in poor adhesion, peeling, and blistering, which affect the coating’s performance.

Extremely high temperatures can cause thermal shock to the coating. This results in a faster surface cure but an inadequate full cure. The coating might not achieve its desired properties for adequate performance. It also might not have enough time to adhere to the surface, which can lead to peeling or flaking over time. Rapid curing can also trap air within the coating, which results in bubbles that may further weaken it.

Recoat Time

Recoat time occurs between the initial and full cure of a coating. Temperature influences it in the same way as these other properties. If the recoat window is shortened due to high temperatures, you will have less time to apply more coats to build thickness. It may also prevent good intercoat adhesion if they are applied past the recoat window.

Place Into Service Time

Place into service time is another property between the initial cure and full cure. If the temperature increases, it will reduce the place into service time. Depending on the project, this can be important for project turnaround. The faster you can complete a project, the faster it can be used, and the faster you can start working on a new one.

Full Cure

The initial cure is affected by temperature first; the full cure will be affected in the long run. Increased temperatures will mean a shorter timeline for when your project has cured and obtained its final properties. Cold temperatures will prolong this final cure. They can also prevent the coating from reaching the final properties at all.

Temperature Guidelines

Control and monitor temperatures during storage, handling, and application. Applying coatings within a recommended range ensures optimal adhesion, coverage, and long-term durability.

A general rule of thumb is for ambient and surface temperatures to be between 40-100°F for consistent, uniform curing. VFI recommends working at room temperature (77°F) for a good middle ground.

Material temperatures are recommended to be at least 65°F to balance viscosity. This will improve mixing and create a smoother, uniform application. It will also ensure optimal flow, coverage, and self-leveling.

The temperature of the material can also be adjusted with high-pressure equipment. This equipment will have heated hoses capable of maintaining temperatures between 135-150°F. High temperatures lower the viscosity for ease of spraying.

Several coatings may be at risk of freezing in storage if they are exposed to temperatures below 40°F. This usually affects the isocyanate (A side). It’s recommended to store them between 60-90°F. If the material temperature has fallen below this range, heating the coating before use is recommended. Some A sides should not be used if they freeze, as they may form small crystals, which will affect the integrity of the material.

For urethanes and some polyurea hybrids, if moisture enters the A side when the container is opened, the material may harden. If the moisture is sealed within the container, pressure may build up, and it could explode. The B side is less sensitive, but if moisture enters, it can cause pinholes and foaming once mixed and sprayed.

During application, the relative humidity should be as low as possible to reduce bubbles during application as well. Additional post-work may be necessary to get rid of them.

Always work in an area with adequate ventilation when spraying, either outdoors or in an approved spray booth. Not having any ventilation can impact the cure of the coating. Use recommended PPE to prevent inhalation and skin contact.

Contact VFI if you need help finding a coating that will work best in your environment.