How to Seal Foam for Durability on Theming Projects

Do you have to repeatedly replace your foam props, sculptures, custom signs, and other structures due to wear? When using foam in various theming applications, you need to be sure to seal it to prevent damage. This is essential for anyone working with foam to enhance its durability for increased longevity. Learning to protect your project effectively can make it practically indestructible for years.

So, what can you use to seal and harden foam? A workhorse in the industry for small and large theming projects is polyurethane hard coats. They offer many benefits, including durability, long-lasting protection, high-quality finishes, and more. If you spend a lot of time carving foam to get intricate details, you’ll want to protect it, so why not protect it with the best option available?

Types of Foam Used for Theming & Attractions

Fabricators may work with a handful of different foams to ensure the strength and durability of their structures. Using foam comes with cost-saving benefits compared to other materials like wood, metal, or concrete. You can also create large and elaborate designs without them becoming extremely heavy. The most popular foams used in theming include:

• Expanded Polystyrene (EPS). This type of foam is made through the process of expanding polystyrene beads. It has an open-cell structure, which creates an uneven and less dense surface. However, it is very lightweight and more cost-effective than other options. It will be messier and more likely to crumble as it is carved, but it is easier to handle and shape with hot wire cutters, knives, and CNC routers. While 1-3-pound foam will work, 2-pound foam is usually the best density for a balance of affordability, ease of use, and durability.
• Extruded Polystyrene (XPS). This type of foam is also known by the brand name Styrofoam and is made through the process of extrusion. It has a closed-cell structure, which provides a smoother surface and enhances its durability. Since XPS is dense, it may be sturdier for large, oversized props. However, it is slightly more expensive than EPS and isn’t as readily available. It mainly comes as panels that you stack up and glue together before carving, which can be a hassle.
• High-Density Polyurethane (HDU). This type of foam is made by combining two components that react and form a rigid, closed-cell structure. It offers more structural integrity because of its high density and is great for use in outdoor environments. It has the ability to be shaped or molded into almost any form. It offers a good balance of durability, weight, and cost. However, it can be more difficult to hand-carve than the alternatives.

Why Seal Foam?

You might ruin your project if you bypass a protective layer and go straight to priming or painting. Some resins, spray paints, glues, and solvent-based materials can dissolve the foam. You’ll want to use a protective coating for the following reasons:

• Protection from wear and tear. Foam on its own is at risk of becoming damaged from abrasion, impact, daily traffic, and more. The last thing you want is for a project you worked hard on and spent countless hours or days creating to degrade in under a year.
• Environmental protection. When your props are meant for outdoor settings, you’ll want to make sure they resist various weather conditions. Sealing the foam with a coating will protect your project from moisture, UV degradation, chemicals, and spills of all kinds.
• Increased project lifespan. If you don’t need your foam project to last, you probably aren’t looking for a protective coating. Most DIYers will go the cheapest route possible because longevity isn’t a priority. If you need your project to last for years and years without issue, you’ll want the strength of a more protective coating.
• Ease of painting. Foam doesn’t always have a smooth surface that is desirable for painting, especially after it is carved. A hard coating can be used to give the foam a rigid and smooth surface for easy painting while also increasing its strength. Sealing is always recommended before painting to ensure proper adhesion of paint to the surface.
• Enhanced aesthetic. Once coated and painted, it will be nearly indistinguishable that the structure is made of foam. The coating provides a smooth, professional finish, which makes it easy to achieve the detail you desire. Once sealed, you can sand, prime, paint, and add any architectural finishes you desire.

Different sealing methods offer varying levels of durability, so choosing the right one depends on your project needs.

Types of Urethane Coatings for Sealing Foam

Urethane hard coats are very prevalent materials in the theming industry for their hardness and strength. Most are formulated in the 65-75 D Shore hardness range to provide hard shell barriers over foam before they are painted.

At VFI, no project is too small or too large for our urethane hard coats. We have materials that can accommodate any job, including brushable and spray coatings.

Fabricators with advanced skills may consider using multiple coating methods for various project needs. Regardless of the material you use, you’ll want to work in a well-ventilated, temperature-controlled environment and use personal protective equipment.

Brush-On Hard Coats

Brushable coatings are typically used by smaller scene shops and prop makers. To save money, many DIYers will use Mod Podge, PVA glue, or paint to protect their creations. However, this won’t protect the prop or sculpture in the long run.

For long-lasting results, there are brushable urethane hard coats available. They can be used for small projects or repairs. They are recommended for intermediate users since they require a bit more skill and care compared to DIY methods.

They typically won’t be used on larger projects since they are more time-consuming to apply and have shorter pot lives when mixed in larger batches. Though they are great when precision for intricate details is desired. Depending on the type of foam used, they can also be used to glue larger pieces together to form even bigger structures.

For tips on using a brushable hard coat, check out VFI’s blog.

Spray-On Hard Coats

The two versions of sprayable hard coats on the market are high-pressure and cartridge-based. Spraying, regardless of equipment choice, is great for even coverage and faster application. While urethane hard coats are pretty fast-setting regardless of application type, spray coatings offer an increased turnaround rate so you can start post-working your project shortly after spraying. These coatings are applied with great precision and won’t leave brush marks.

Whether you use cartridge-based or high-pressure equipment will be based on project size and volume. Cartridge style is a great application method for skilled fabricators ready to take their prop-making to the next level through spraying. It’s also great for individuals who want a cost-effective, portable experience.

For tips on using VFI’s cartridge-based Qwik Spray applicator, check out our how-to blog.

High-pressure equipment is better for big jobs and frequent spraying. It’s also going to give you a smoother, more consistent finish, whereas low-pressure might create a bit of an orange-peel texture. It must be used by advanced fabricators who are experienced and trained to spray.

Why Urethane Hard Coats?

• Sealing Abilities. As a coating, urethane creates a smooth, seamless barrier over the surface. This prevents water intrusion from weather events, random spills from placement around heavy traffic, and any other unexpected occurrences that could damage the foam.
• Durability. Urethane’s hard-shell exterior offers great protection from impacts and abrasion, securely shielding the foam layer beneath. Other coatings can’t build thickness quickly and are more susceptible to cracking or breaking. Urethane builds thickness in fewer layers for increased protection, and it’s still relatively thin and won’t add too much weight to the project. In addition to its durability, it is also offered in fire-tested formulas for indoor and outdoor use.
• Flexibility. Something that urethane offers that not all coating materials do is good thermal cycling. This means that it can be placed in outdoor environments where temperatures may fluctuate, and it won’t crack from the movement. Other, less protective coatings will be brittle and not flexible enough for the surface.
• Adhesion. Urethane coatings are great at penetrating and locking into the foam surface, so you don’t have to worry about peeling or cracking from poor adhesion. Even as the coating penetrates the surface, it lays flat for a desirable, smooth finish. You also don’t have to worry about the coating eating the foam like some solvent-based materials might.

Contact VFI if you need help choosing the right urethane hard coat for your next theming project.