Rosco foamcoat is a special purpose acrylic based coating, similar to a heavy gesso, used for adding strength and textured surfaces to all manner of materials used as props for stage sets. Like artist's gesso, it can be easily tinted, thinned and used for any range from smooth through rough finishes. The handling and finishing properties are very similar to those of dense acrylic based gesso.
Hard Coating for Model Scenery
Foamcoat is a water based coating used by stage scenery and prop departments mainly for adding a hard durable, flame retardant finish to light weight foam scenery items. It can be used on a variety of surfaces, including primed wood, concrete block, primed fiberglass, paper machÃ©, and fabric. It is flame retardant and water resistant when dry.
Foamcoat can be applied with a brush or roller or through a hopper spray gun. It can be thinned with water and tinted with artists tints or acrylic paints. Fabric can be dipped in it, then molded, or added as a top layer to strengthen a foam shape. In its untinted state it is an eggshell finish off white. It cleans up easily with soap and water before it sets. A coat will dry to the touch in 2-8 hours, with a full cure in 24 hours. Like gesso, it is workable through a long period, depending on the working temperature and humidity. It can be used in silicone moulds to produce fine shapes.
Unfortunately for the hobby market, it is only sold by the manufacturer in one gallon and larger containers. It has a composition very similar to artist's gesso, being made of acrylic polymer with calcium carbonate. It is very dense, 1 gallon weighs 16.6 lbs.
As Foamcoat is extremely dense, it must be stirred with a mechanical paint stirrer to mix. If it is kept sealed and away from extreme temperatures, it has a minimum shelf life of two years.
Using Foamcoat for Modelling Terrains
Foamcoat adheres well to most forms of foam, without first preparing the foam with an undercoat. This means that unlike many model railroad foam coating systems, which use latex paint, spackle or drywall filler, and then texture or paint on top of that, Foamcoat can be colored and applied directly to the foam base. As Foamcoat can be sanded to a smooth surface, or textured with any number of standard painting tools, it can be applied with spatulas, foam, or stiff brushes to create textured areas, or applied and wiped off with a sponge before it sets, to create smooth areas for stream beds or snow. As it is denser than most artist's gessoes, it can be applied directly to layers of foam to fill in cracks or smooth over and cover glued layer seams. It can be thinned, to sink deeply into cracks between stones on stone walls, or left thicker, to fill in or over problem textures (styrofoam bead board or beaded styrofoam for example). It can also have texture added to it to create tree bark or textured surfaces for particular finishes (sand or dirt for example).When dry, Foamcoat remains slightly flexible, but does not flake or chip like drywall compounds can do. As Foamcoat can be tinted, any chips that do occur in a tinted coat will not be as noticeable as will chips in paint over filler.
You can see an example of Foamcoat in use in the tutuorial on making stone walls from foam. Foamcoat was used on dry florist's foam, high density insulation board and styrofoam bead board. Foamcoat successfully disguises stryofoam bead shapes in a single coat.
Advantages Over Using Gesso
Foamcoat appears to be stronger than artist's gesso, but that is likely due to its dense filler of calcium carbonate. If you use a particularly strong or dense gesso, the coats may perform similarly. Foamcoat sands to a similar surface as gesso. It does appear to adhere better than gesso to surfaces like concrete, and some forms of foam with less 'tooth', this may be due to the proportion of acrylic in the mix.
Without thinning, Foamcoat appears to be roughly twice as dense as regular gesso. Single coats fill over high density insulation board (extruded foam board) very easily, adhering strongly to the foam without any prior sanding or roughing of the surface.
Difficult to Source The only difficulty with foamcoat appears to be its availability and its shipping weight. It is available throughout North American and Europe, usually available from specialty paint stores, commercial photography shops, foam stores and suppliers to the stagecraft or light weight commercial prop trade. Some 'foam coat' products may be available tinted from some speciality suppliers in smaller quantities, most do not give their ingredients. Hotwire Foam Factory also sell a 'Foam Coat' product which is available in smaller amounts, but their's is a powder, ingredients not listed, although it appears to be either plaster or cement based (possibly a grout) as it sets up quickly. Hotwire Foam Factory Foam Coat needs to be mixed with water and requires the addition of a separate, likely acrylic, extender (the ingredients are not listed) to strengthen it and make it adhere to all surfaces.