FAQs Gluing and Coating

Coatings and Glues FAQs

Common (and not so common) Questions & Answers

Frequently Asked Questions about Gluing, Protecting and Coating Foam

Click here for the Foam Coat Mixing Formulas PDF

Q: Can your Foam Coat be used inside and if it is fire safe?

A: Foam Coat can be used inside and is not only fire safe, but inhibits fires. For those seeking fire safety approval when using foam, we suggest turning in the Material Safety Data Sheets (MSDS) and/or having the fire inspector testing a sample. Usually the problem comes up with artists making stage props using uncoated foam. The fire people are especially strict when there will be a large audience in an enclosed area. When they see the MSDS’s for the foam, they usually give the go-ahead because foam is less flammable and less toxic than wood. You can hold a torch to EPS foam and it will stop melting/burning the second the flame is gone. The ‘smoke’ is mostly hydrocarbons and water vapor. This helpful PDF from EUMEPS goes over the behavior of EPS in case of fire.

The worst case scenario is having to coat the foam with Foam Coat. Below is the section from the MSDS showing the fire data:


Flash Point (Method Used): Non-combustible.
Extinguishing Media: Use extinguishing media appropriate for surrounding fire.
Special Fire Fighting Procedures: None
Unusual Fire and Explosion Hazards: None
Special Fire Fighting Protective Equipment: None

Q: What types of paints do you recommend using? Interior or exterior? Acrylic or latex?

A: Always use water based paints. Acrylic or latex paint is fine. If your project is going outside use exterior paint as it will not fade as fast as interior and will protect the foam longer. Always test the paint on a scrap piece of foam since there might be additives that dissolve foam. It can take a couple of minutes for the foam to dissolve. Unfortunately, some paints have mild solvents that will slowly eat at foam for years but will seem fine at first.

Q: How can I slow down the set time for Foam Coat so it doesn’t harden before I finish applying it?

A: We recommend adding latex paint instead of water. It doesn’t seem to weaken the Foam Coat and can give you up to well over 40 minutes working time if you mix it straight with no water. I don’t think that this has any affect on the longevity of the Foam Coat. I wouldn’t suggest any of these techniques in combination with the liquid fortifiers. One of our customers said suggested adding a couple of packets of sugar to the Foam Coat: If sugar is present in concrete, it delays setting time of concrete, so sugar act as a retardant. If sugar presents 0.5% to the weight of cement, it delays setting time 2-3 hours. and if sugar presents more than 2% to the weight of cement, then concrete setting delay several days or more. Click here for the Foam Coat Mixing Formulas PDF.

Q: How do I protect foam when it is outdoors?

A: The cheapest and easiest coating is outdoor latex house paint. If the foam will be in an area where people and animals won’t be banging into it, it will outlast painted wood because shrinkage, expansion, or rot will not occur with polystyrene foam, as it does with wood. We now have a complete Foam Coating System with several options for protecting your foam. We have both an All-Purpose Foam Coat and an Exterior Foam Coat.

Our Exterior Foam Coat is ideal for coating foam for outdoor use. It can even be applied to foam that is going below grade. It is super strong and adheres extremely well to foam. Boost liquid fortifier will work well with Exterior Foam Coat, but not Bounce. The Exterior Foam Coat takes longer to set up and dry, and gets stronger over time. It also has a rougher finish than the All Purpose Foam Coat, but can be troweled smooth.

The Foam Coats are concrete based products, so when applied thick enough (at least .5″ thick) the coating will be very difficult to break or crack. We always recommend adding some Boost liquid fortifier, as it will greatly strengthen and weatherproof the Foam Coat. The Foam Coat is slightly porous, so use an exterior paint, or other sealer over the Foam Coat. If you add Bounce to the All-Purpose Foam Coat instead of Boost, it will make a flexible waterproof coating. We also offer Grit in either medium or coarse, which adds a stone-like texture to foam.

If you are looking for super strength you can fiberglass and epoxy the foam. Many kayaks and windsurfers are made this way. Never use resin directly on the foam, as it will dissolve polystyrene. You can use a coating of Foam Fusion glue as an insulating barrier from the resin.

Our newest coating product is our Styroplast, which is a brush-on encapsulant with a fast set time that is designed to provide an impact and fire resistant shell for numerous substrates including EPS/Styrofoam, insulative foams, and wood. It is a two component slow cure polyurethane coating that offers superior hardness and greater moisture resistance than epoxies and resins. For more information, see the product page here: it is available in quarts and gallons.

Q: I made a foam background for my aquarium – what can I use to safely coat it?

A: Patrick of Deep Sea Aquarium Maintenance has tested two Krylon sealant products that did not change the pH of his test water. Both Krylon Fusion for Plastic is available in clear and Krylon Conservation Varnish is available in gloss and matte. These products probably cannot go directly on the foam, but they will work great over all of our coatings. Patrick used All-Purpose Foam Coat with Bounce to coat his foam background and then sealed it with five coats of the matte finish Krylon Conservation Varnish. An aquarium blog also reported that the Krylon Fusion for Plastic was their sealant of choice and to let it dry for a week to fully cure or it might flake off where water is rushing across it when used in a larger outdoor pond with a waterfall.

For larger projects Patrick also recommends using Pond Armor, which provides a water proof non-toxic barrier for aquatic environments, old or new. It is reportedly fish and plant safe. Others have told us they smear silicone aquarium sealant on whatever they need to seal.

Our Exterior Foam Coat is rated for below grade installation and withstands wet weather. Our Styroplast is a completely waterproof encapsulant. Both of these products should be sealed to be made fish-safe.

Q: How do I get the Foam Coat smooth?

A: If you tap on the Foam Coated object, the Foam Coat will momentarily liquify to smooth out the brush lines and other imperfections. Also, much of the smoothing (or texturing) can be done as the Foam Coat is setting up. A clean, wet or dry metal trowel or putty knife works best. It can even be sanded just after it sets, but before it dries, much more easily than after it is completely dry. Best to use a wet-and-dry sandpaper, so if the paper clogs it can be more easily cleaned for reuse.

Q: I’m having difficulty with the foam coating. I’ve had one large piece of foam that has bowed as a result of the coating. I also have the coating chipping off, even with using boost. Do I have other options for a durable coating for high traffic areas?

A: The bowing of large thinner sheets of foam when coating has been a problem for many years. A shaper friend of mine once made me an EPS surfboard covered with fiberglass and epoxy that was warped out of shape. His cure, which worked, was to put a 1/16″ wooden stringer in all his EPS surfboards. He just sliced the 18″ wide foam down the middle and glued in the thin piece of wood.

As far as chipping, is it not sticking to the foam, or is some of the foam coming off with the chip? See if there is any trace of foam on the chipped off pieces. The Boost makes the Foam Coat so sticky that if I forget to clean my trowel I have to use a grinder to remove it. It will not just chip off. If it is applied thin and is cracking, you should consider putting it on thicker, and/or switching to Bounce as a fortifier, as it will flex when impacted. We recommend Bounce for stage props, and Boost for backdrops. Neither will chip when applied thick enough.

Our newest coating product is our Styroplast, which is a brush-on encapsulant with a fast set time that is designed to provide an impact and fire resistant shell for numerous substrates including EPS/Styrofoam, insulative foams, and wood. It is a two component slow cure polyurethane coating that offers superior hardness and greater moisture resistance than epoxies and resins. For more information, see the product page here: it is available in quarts and gallons.

Q: I need to make a large non-loadbearing fake rock as a prop for my daughter’s dance performance. I plan to use either pink or blue foam insulation sheets (8’x4’x2″), cut and glued together, and then carve the desired shape from that. What I need help with is which coating to use to make the final product durable and paintable, and I’d also like to make it flame retardant. I also will need to buy glue to make blocks out of the insulation sheets. I need help with which coating to use – is there one that is both strong and flame retardant? The prop will need to travel between competitions and performances and might need to take a little abuse.

A: Our Exterior Foam Coat looks and feels like stone. You can create a super rough or a semi-smooth surface as it dries. Go over it with a coarse brush for a rough texture, or a metal trowel for a smooth finish. Make sure that the glue that you use can be cut with a hot wire. If you are using flat sheets you won’t have to put the glue on very thick. Our Foam Coat is flame retardant. Most prop builders use 1lb EPS foam for their larger props, and the Blue or Pink foam for small detailed props. The Blue and Pink foams are very strong, but add considerable weight, cost, and take longer to cut. Our Foam Fusion glue will give you permanent bonds to create your foam blocks.

Q: I have a question about your Foam Fusion glue. I did a test with it, gluing some smaller pieces of foam prior to starting the project and it was phenomenally strong and we were very pleased. However, when we built the large set and after letting it sit for a day we started carving into it and the glue is still gooey and not cured, so the layers of foam are coming apart. Once those exposed areas get some air overnight they get hard, although they’ve already separated. I believe and am hoping the coating will help to hold it in place. It seems as though the glue just needs air to cure so when it’s trapped in between two large sheets it doesn’t cure. Is this typical or an application it is not intended for?

A: The Foam Fusion glue is made to dry even without air. If you were using a nonporous foam like the Blueboard foam, then it might take an extra long time to dry, but with the EPS foam you are using it should dry in 24 hours. If it is put on too thick this will greatly impede the drying time. Less is more with this glue. If you don’t have perfectly flat pieces of foam, you can thicken the glue with small amounts of Foam Coat. The Foam Coat will also hasten the set up time, but you can’t cut through Foam Coat with a hot wire. If you are using non-porous foam, or need to glue foam to a non-porous surface, then a liquidy mixture of Foam Coat and Boost will do the trick – this mixture will stick to almost anything and it sets up really quick too. We also have a spray glue for instant tack. To really speed a project along you can use the Foam Fusion, but then use low temperature hot glue to tack the foam together in a few places.

Here’s a testimonial from a customer regarding our Foam Fusion glue: “I tried the sample of Foam Fusion, looked at it, and thought I could substitute Elmer’s glue for it. When I did my project, I was very sorry I tried the substitution. Two weeks later, the foam pieces were falling apart with the white glue being totally wet like when I poured it.

I had the HWFF people explain that Elmer’s (or plain white glue) is air dry, while Foam Fusion is a chemically drying product.  I will never make that mistake again, and I wish I had the two wasted weeks back!”

Q: I can’t find any local suppliers of large sheets of foam. I’m planning on making gaming terrain and need sections thicker than the 2″ max I can find at any of our local diy stores. If I use PVA glue to stick two, or more, sheets together, will the layer of glue ruin the wires on the shaping tool, or the blade of the hot knife? Should I carve everything first, and then glue it? In the past, I’ve been able to find packing foam or other spare chunks of foam for terrain pieces, so I’ve never had the need to glue unfinished pieces together. Any advice?

A: Some people just use wood skewers to temporarily hold the foam sheets together then glue them after they are carved. You can also use our spray glue, or Foam Fusion brush on glue. As long as they are not put on too thick, which doesn’t help the bond anyway, the glue can be cut through with our tools, though it does slow the cutting down. You can spot glue your sheets so you don’t run into the glue as often. I have never used PVA glue. We have found that some glues have very slow working solvents that will dissolve the foam after a year or two. The EPS foam glue from Liquid Nails did this to a large project that I worked on, and every place I glued had a large cavity.

Q: I build foam RC model airplanes, I am looking for a foam-safe, fast setting and strong glue. Foam Safe Super glue is fine for gluing small parts, but expensive for large projects. Do you carry anything that would fit my needs? I bet it would become very popular with our club members as well.

A: One of our RC Airplane building customers swears by our Foam Fusion brush on and Shelby 277 spray on glues. “I am a real fan of your Foam Fusion for the construction of my RC model airplanes. It is absolutely the strongest glue I have found.”

If you need a faster setting glue, we also offer StyroGoo, which is an instant tack foam-safe glue. It is perfect for permanently adhering foam, foam rubber, paper, glass, fabric, wood, plastic, metal and cardboard.

Q: I want to sandwich an aluminum piece inside two layers of hot-wire-cut foam, presumably with using the same adhesive (Foam Fusion?) for both the foam-foam and foam-metal bonds. No doubt the foam-metal bond won’t be so great because Foam Fusion wasn’t made for metal, but I’d sure appreciate it if you could please comment on just HOW poor the foam-metal bond will be, and what surface treatments I can give the metal to make the bond as good as possible.

A: I had a similar project a couple of years ago. I had made foam elements to go up on our new Hot Wire Foam Factory building which is metal. Since our Foam Fusion will only stick to porous surfaces, I made the mistake of using Liquid Nails, the one they make for EPS foam. Well, low and behold after a year the elements started falling off. There were holes wherever the Liquid Nails was applied. I had tested the Liquid Nails for two weeks before applying the final pieces and it slowly worked its way through the foam over the following months. I got to thinking about our Boost, a liquid Foam Coat fortifier. I have been using Boost with foam for several years and it does not dissolve the foam. I had used Boost, Foam Coat, and Coarse Grit to make a stucco coating for the metal sides of the building and it came out excellent. It doesn’t peel or chip when the metal flexes. I hit a test piece with a hammer and it just dented it. It makes the Foam Coat stick like crazy to anything. If you don’t rinse it off your metal drill paddle, you won’t be able to even chip it off when it dries. So, can you guess what I am regluing the foam elements back to the building with? The Boost fortified Foam Coat is the best foam to metal glue that I think you will find. Later, I glued some smooth ABS plastic hangers to some 4ft x 7ft Foam Coated panels for an exterior wall mural using Boost fortified Foam Coat, and it also worked great. Another advantage is that you can make it pasty so it won’t run off of vertical surfaces.

Q: I am trying to glue foam together and the white glue by Elmers isn’t holding. What do you suggest? It is a large item and I need it to hold firm. Any suggestions?

A: Elmers white glue takes forever to dry. That’s why we came out with our own formula for Foam Fusion. Be conservative and don’t put it on too thick. If the foam is irregular and you need some fill, just mix in some of our Foam Coat to make the glue pasty. In either case, it will set up in less than an hour, and completely dry overnight. The foam will tear before the glue lets go!

Also, there are no solvents that will eat through the foam – we used some Liquid Nails that was advertised as EPS foam safe, only to have it eat through the foam one year later. You can use little dots of low temp hot glue to hold your project in place if you need to be working on it while the glue dries. Our tools will cut through Foam Fusion, but not with Foam Coat mixed in with it. If you are gluing foam to a non-porous surface, try a mixture of Boost and Foam Coat. That stuff will stick to everything. Wash it off your tools before it dries, or you will never get it off!

Q: To stop birds and squirrels from eating at the foam on foam birdhouse and feeders, is it best to use your foam coat? Will this protect the foam from these critters?

A: Our Foam Coat is a concrete based product, so when applied thick enough it will be bird and squirrel proof. We had an artist who made a foam sign that was just painted with outdoor latex house paint that survived 10 years of sun and rain, a few freezes, and a storm with 100mph wind gusts, only to have the tops of some of the letters pecked away by pigeons that began roosting on the top edge of the sign. I always recommend adding some Boost liquid fortifier, as it will greatly strengthen and weather-proof the Foam Coat. Use an exterior paint, or other sealer over the Foam Coat. Several customers have had experience with birds, and now I hope you will be the first to report back to us on squirrel proofing your creations.

Q: I’ve been designing a Halloween costume for the past 2 weeks and I’m about ready to start crafting it. I was interested in using foam to design an armored chest & back piece, but wanted to fiberglass it for the smooth and hard shell. I quickly found that fiberglass resin melts through Styrofoam which I got at a local craft store. Would Foam Coat give me the results I am looking for? If not, would it be safe to fiberglass over the Foam Coat after it is applied and dried on the Styrofoam. Please give any tips or hints if you have any.

A: You can coat the foam with Foam Coat or a layer of Foam Fusion to protect it from the resin. Many surfboard makers are now using marine epoxy instead of resin because it won’t melt the foam and it is even stronger than resin. Make sure you use a thickener made for epoxy, or the epoxy will run off your foam before it dries. If you want to try just using our Foam Coat, I strongly recommend that you use some of our Boost or Bounce Foam Coat fortifiers. Boost will allow you to apply a thinner layer of Foam Coat with the added strength that you need. Bounce will make the Foam Coat rubbery. To give it its ultimate strength, use our new Mesh to wrap your foam like a mummy. Smooth it as much as possible before it dries, as it is very tough to sand when dry. Sometimes I use sandwich wrap to press against the drying Foam Coat to smooth and contour it as it dries. I don’t know if fiberglass will absorb this mixture or not.

Q: I am a photographer and I am planning on making some photo props but I want them smooth & very strong. What do you suggest?

A: We have many still and motion picture studios using our tools to make foam props. Look in our gallery for many samples. Especially take note of the Foam Signs and Theatrical sections. Some of the foam artists share their techniques. Our All Purpose Foam Coat is very hard, and can be applied in multiple layers for extra strength. If you tap on the foam sculpture right after it is coated the Foam Coat will re-liquefy and smooth itself out.

Our newest coating product is our Styroplast, which is a brush-on encapsulant with a fast set time that is designed to provide an impact and fire resistant shell for numerous substrates including EPS/Styrofoam, insulative foams, and wood. It is a two component slow cure polyurethane coating that offers superior hardness and greater moisture resistance than epoxies and resins. For more information, see the product page here: it is available in quarts and gallons.

Q: Living in Arizona, and contemplating using foam for building a mountain in a G scale garden railway, I am concerned about UV deterioration as well as heat. What is your experience with surface temps reaching 140 Degrees?

A: EPS foam is used for insulation and gets much hotter than that for many years with absolutely no deterioration. I suggest that you at least paint the foam with a good exterior latex paint to protect your project from UV, as the surface will eventually get a yellow powder on it.

Q: Have you heard of anyone creating their own faux stone veneer for the outside of their home, and if so, with what degree of success?

A: We don’t have any examples of faux stone veneer in our gallery yet, but you can get some pretty good ideas by looking at the tombstones people have made. Our Exterior Foam Coat looks and feels like stone. You can create a super rough or a semi-smooth surface as it dries. Go over it with a coarse brush for a rough texture, or a metal trowel for a smooth finish. Also, look at the rocks that Boulder Image has built for their waterfalls, also on our website. I talked to an artist that was restoring the outside of a brick building who said he and his customer were very happy with the red brick veneer that he created. I see no reason that you can’t create any exterior finish you want with a foam substrate. Click here to see the realistic ‘woodwork’ that a theater group created for “My Fair Lady” (not to mention the stone walls and plaster crown molding)?

Click here to submit your questions and/or tips