What Is a Brushable Hard Coat for Foam?

A brushable hard coat for foam is a coating formulated to be applied by brush or trowel rather than through spray equipment. These coatings are used to protect fragile surfaces such as Styrofoam, EPS, and XPS.

Using a brushable hard coat heavily depends on your unique project. If you’re a sculptor who works on small EPS foam projects for theme parks, film and theater, or art exhibits, you probably don’t require large, expensive spray equipment. A brushable coating can be much more effective for these applications because, as the name suggests, all that’s needed is a paintbrush.

Types of Brushable Hard Coatings

While various hard coatings exist, most are not formulated for brush application. This is because most hard coatings are fast curing, meaning they dry or become tack-free in under a minute. Due to this speed, a spray method is the best approach. A brushable coating has a slowed pot life with good hang to allow applicators ample time to apply it to foam and other surfaces.

Two specific formulas of brushable hard coats for foam that will provide the best protection are polyurethane and epoxy. The material you choose will depend on the surface you’re protecting, the shape of the structure, the required finish, budget, environment, and turnaround time.

Urethane

Urethane brushable hard coats for foam feel almost like smooth plastic when they cure and are generally tougher than epoxies. Similar to sprayable hard coats, they encapsulate the entire foam piece, making it water and impact resistant. It’s recommended to apply these coatings a bit thicker for thorough protection. With a high thickness, the coating will hang vertically in up to 40 mil passes without sagging. The longer you’re working with the material, the more it will thicken as well.

While they are not UV color stable, this isn’t normally an issue since they are typically top coated with primers and paints in the finishing process. Once cured, they can also be sanded if the surface is not as smooth as desired from brush application.

When using a polyurethane brushable hard coat, a big limit compared to sprayable coatings is it has a longer cure time. Sprayable coatings can cure in a few hours while a brushable urethane can take a minimum of 8 hours.

VFI offers two different formulas for brush application:

• VFI-2519 75 D Brushable Hard Coat. At 75 D hardness, it’s about 10 D durometer higher than VFI-2626. As a harder and stronger polyurethane coating, this material offers higher tensile and tear strength for extended protection from impacts. This coating is not fire tested and has no fire retardant or resistant properties.
• VFI-2626 65 D Brushable Hard Coat. While this material has similar qualities to VFI-2519, it has slightly lower tensile and tear strength at a lower durometer. The coating is recommended over its counterpart in indoor applications, as it is capable of passing the UL 94 V-0 combustion test.

When applying one of these hard coats, you can mix up the material in smaller quantities, so you won’t overuse material. Mixing smaller quantities also helps extend the pot life.

Epoxy

Epoxy brushable hard coats form a solid, plastic-like surface over foam to protect it from impact and weathering effects. Because epoxies can be hazardous when sprayed, they are usually only applied by brush or roller. They’re also applied in thin layers, so they won’t always provide as much protection as urethane coatings.

It’s recommended to use them on projects that are kept out of reach and won’t endure heavy impact. Too much impact can make these coatings crack or break. However, they are a more desirable option if you are working in environments where moisture and humidity are a concern. Their neutral-colored surface can easily be sanded, primed, and painted over.

Like all brushable hard coats, epoxy cures slowly. It’s even slower than urethane brushable hard coats and can take almost double the time to cure at about a 16-hour minimum.

Why Use a Brush Method Over Spraying?

The choice between using a brush on or spray on coating will depend on your project’s needs, including your budget, the size of your project, the surface texture you desire, and turnaround time requirements.

• Cost-effective – High pressure spray equipment can cost thousands of dollars, so buying brushes is an inexpensive option. While it can be labor-intensive to use a brush, it is recommended for small projects, so material and time waste is not an issue. However, if you consistently work on larger projects, spraying may be the more desirable method. To achieve the effects of spraying at a lower cost, there are quick spray alternatives, such as VFI-6171 70 D Qwik Spray Hard Coat.
• Excellent control – Spraying can be great for larger projects, as it covers them quickly and evenly, but it’s not always suitable for small pieces. It can hinder details, whereas a brushable coating would be better for small corners, intricate designs, and specific curves. Because you don’t have much control over where the material goes when spraying, you must mask and prepare adjacent surfaces to protect them from overspray. Also, more material is used due to overspray, but brush application allows you efficient control over material used.
• Even, uniform coverage – Those with limited experience using spray equipment may encounter overspray, drips, runs, and uneven spots where material is too heavily built up or too thin, offering little protection. Brush application is much more straightforward, so you achieve consistent coverage for long lasting protection. Brushes are also better at getting into hard-to-reach, tight corners where spray coatings can’t.
• Easier application and cleanup – Applying coatings with spray equipment requires training, so you know how to spray at a consistent distance for smooth application. When brushing, you don’t have to be concerned with spray techniques, chances of overspray, or cleaning spray lines once you’re finished. Cleanup is even more effective if you use disposable paintbrushes. Also, if the coating cures with any brush marks, the surface can be sanded before it is primed or painted.

Applications for Brushable Hard Coats

When protecting foam, a brushable coating is most advantageous for smaller, delicate, and detailed projects. We’ve seen our polyurethane coatings used on custom signs, film and theater props, holiday décor, art sculptures, and more because of their strength and durability. Even when working on larger projects, you can brush the hardcoats onto smaller pieces before assembling them into the final structure.

Brushable hard coats for foam also work as a good repair material. While these coatings are durable, they aren’t foolproof. Before extensive damage can happen to the foam being protected, it’s best to patch up areas as quickly as possible. Rather than spraying a new coating layer, brushing material onto small cracks and punctures is easier and saves material. Material can be mixed in small batches, and you won’t have to worry about cleaning spray lines.

Contact VFI if you need assistance finding the best hard coat material for your foam project.