"Coating and Sealing White Foam?" Topic

I've got a bit of surplus, white, high-density foam (not the cheap, pebbly, stuff).

This material has an open-cell structure on its sides, but on the larger, flat surfaces, looks pebbly, but is very smooth and resilient. Rather like a soft plastic. It is pretty high density, and bounces back nicely, when fingers are pressed against it (it won't leave permanent depressions in the foam, after doing that).

Not sure what the correct name of the foam is, but I think it is like the type they use to make surfboards with, and/or use for packing large, heavy, valuable objects on/in crates.

It's not the usual, blue or pink, PVC styrofoam, which is much more rigid.

Anyway, I'm interested in creating a more rigid, but flexible coating on it, to make a custom model, and was thinking that perhaps some auto-body putty might work, since it's pretty durable, reasonably inexpensive, and easy to work with. Ideally, I'd like to coat all the foam with it, and to perhaps scribe in some panel line detailing too.

So, has anyone worked with this stuff, and tried a similar, large-scale application, before?

I've used it on metal, but not foam.

I'm looking at a model about a foot long, or more, and ideally, would like the Bondo to be able to flex a bit, and/or to give it a nice, hard shell coating.

I suspect I could use fiberglass fabric and resin, perhaps followed by a gelcoat, but that stuff is expensive, and time consuming to work with, so I'd prefer just to try the auto-body putty first, and then perhaps seal that with a clearcoat, or a few coats of paint.

Thoughts?

I've never tried bondo. For sealing/texturing foam for terrain, I've always used lightweight spackle. It works well, but I don'y know if it would meet your flexibility requirement. For foamie R/C aircraft, I've often used a compound of water, future, and talc that seals the foam and (after sanding) gives a nice smooth surface.

Doug

Latex paint is what I've used in the past

In the U.S., go to Sherwin Williams and look for elastomeric roof coating. It is used to seal roofs and stays flexible when dry. It comes black, white or gray. Unfortunately it is only sold in 1 or 5 gal. sizes. It seems pricey but when compared to Woodland Scenics flex paste, the other option, it is cheaper.

I've always wanted to try the rubber tool dip stuff.

Harbor Freight sells Plasti Dip. It's $8.99 USD for 14.5 oz without a coupon ($6.75 with 25% off).

Here's a description from the website:

Plasti Dip is a multi-purpose, air dry, specialty rubber coating for a variety of items. It protects against moisture, acids, abrasion, corrosion, skidding/slipping and provides a comfortable, controlled grip on the handles of screwdrivers, wrenches, pliers and other tools. Plasti Dip bonds to wood, metal, concrete, foam and almost any other surface.

It sounds as though you are describing foam rubber? Is it the stuff they use for padding upholstery?
In any case, you will probably be better off with latex caulking. Latex paint too. These are pretty cheap materials. Very flexable. Be sure the caulking is pure latex to avoid a chemical surprise.

Thanks for all of the tips.

I did a little more searching, and apparently the foam I have is also called "foam plank", and/or polyethylene foam. It is a fairly rigid foam, that has some give to it. Children's foam swimming pool noodles are made of this material.

It's listed as a low-density foam (as opposed to my original high density description), but is resistant to tearing, compression, and also, glues. Given the latter issue, I'm not sure it will really work for my needs, unless I can get a bit creative.

They do sell a spray glue for commercial applications, but it's crazy expensive, at $75 USD per 50 ML (about 1.67 ounces). They also sell a small tube of it, of the same size, for around $115. USD

Therefore, unless I can find a contact glue that is suitable, or can make the model from a single piece, I doubt it will work.

Polyester epoxies supposedly eat the stuff, but apparently some epoxies will work on it. Not sure about the body putty/bondo car repair filler, so will need to check into that further.

I may be able to get around the gluing issues, if I choose the right size and shape of foam to start with.

I will want to apply some sort of outer skin to it though, to permit painting, and/or scenic detailing to the model.

Latex paint is the way to go. Cheap and most places will blend color to match anything.

Thanks for the tip on the paint, but I need to make the rough surfaces smooth as well, before painting.

Some parts are smooth, but others are rough, and have an open cell structure on the sides.

link
I'd stick the thin (about 1/8 inch) foam sheets to it to make it smooth. Just use PVA to glue. This is the kind of stuff every craft store sells for cutting out shapes for pictures.If its only a foot long, it will work fine.
The various fillers you've mentioned will probably work, but sounds very messy.

Why don't you just throw it away and use the blue/pink stuff that everyone else uses?

I may need to consider that, but it's a shame to waste the other material, if I can use it.