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Hey all,

I'm working on making a 4x6 table, the center of which is a piece of 1.5" thick Styrofoam insulation. I plan on carving it down into hilly terrain, but I'm unsure of how to seal it to stop the foam from coming apart/flaking. Does anyone have any advice?

If you're using the extruded styrene insulation foam, it's actually pretty resilient, on its own. Edges and corners can get a bit chewed up if you're rough with it (soft, sloping hills avoid the issue), but you needn't go crazy trying to make the surface bulletproof. As you may know, the propellant from (non-"foam safe" specialty) spray paints will melt the surface, so most people seal the stuff, anyway.

Latex/emulsion paint (house paint) is a popular choice, as it's relatively cheap and decently hard-wearing, thanks to a slight degree of flex in the cured coating - a mixture of PVA glue and cheap acrylic craft paint gives similar results, if you don't want to buy new paint for the project. Further additives, like construction adhesives, drywall filler/plaster, etc. can make the coating harder or more flexible, affecting both working behavior and durability. Some people mix fine sand right into their coating, texturing the surface while they basecoat.

There are specialty products available that actually do make the surface incredibly hard-wearing, but that's an expense I can't justify. If you're interested, check out the videos by Terranscapes on Youtube - he reviews both FoamCoat (gypsum cement) and StyroPlast (polymer), by the Hot Wire Foam Factory (I think those were the names, at least).

Sealing polystyrene and Styrofoam is tricky unless you have the right stuff. The issue is that there are solvents and oils in the sealer that can eat your foam. The easiest way to fix this is to go to your local craft shop (not model shop) but a place that sells paints, canvas, frames etc - and look for some stuff called Gesso. It is a mixture of white paint with chalk and other things that seal the foam. It holds paint really well (it is designed to seal canvas). Make your model, paint on the Gesso and let it dry, then you can prime, paint, base and seal from there making the foam impermeable to the sealers. It does increase the weight of the item though...Also, dont be afraid to coat the item once or twice. you can water it down so its not so thick, but you will want multiple coats if you go that route.

plain as that though, seal it up, prime it and paint

I've had good inexpensive results with Elmer's wood filler (with a few drops of water to make it more spreadable) coated with Elmer's wood glue (with a few more drops of water to make it more brushable) less than $10 and ready to paint.

Edit: DO NOT attempt to kill both birds by mixing the wood glue and wood filler together though, or you'll get a nasty brown rubber lump.

Edit #2: I've tried styroplast as well, and the end result wasn't much different than the wood filler. Plus the surface cracked when I dropped it. So I still prefer wood filler.

Go to a larger construction supply house and pick up some foundation foam paint. You can get a large container for $20 or so, and it is safe to use on all foams and durable enough to withstand things like weed eaters running up against it repeatedly. Comes in a variety of types (hard, flexible, textured, smooth) so just choose the one which suits you needs best. You can apply it with a brush or roller, and square up edges and corners with a putty knife.

You can also get hard coats from companies like Hotwire Foam Factory. They work in much the same way as the foundation coatings, but tend to be a bit finer, so you can get better detailing in the foam itself.

The final option isnt available for everyone (at least reasonably priced) but you can have one of the two part epoxies sprayed on as well. It is the same stuff used to create finishes durable enough to withstand use on movie sets and what not, and the cost isnt too expensive, but the application is more difficult...so you often want to have it done for you. If you have a local company who can do it, it is affordable, but shipping on bulky items can often cost more than the cost itself.