Roughing up foam

Does anyone know some good ways to rough up some foam a little bit without destroying it? I'm trying to make some cobblestone on styrofoam with our stamp. The stamp works well for shaping the foam out, but the stones come out very flat. I used some spray primer to eat at the foam a little, which seems to work, but only if you just spray a little bit so it's tough to replicate. Anyone have suggestions on adding some texture so the stones don't seem so flat?

Are you using normal styrofoam? I guess not since that already has a texture (which wouldn't work well).

You can try to get a stone (a real one, with a rough surface) and hit that on the foam. This is a tip I got from the Gidian-Gelände forum, which has some of the best scenery guys around.

I found I get a nice texture to the foam by simply sanding it. A 50 or 60 coarse grit works nicely. A circular motion gives a slightly rougher texture than a normal back & forth motion...oh, & use a sanding block, & avoid inhaling the dust.

This is what the foam looks like. http://www.tabletopgeeks.com/cobblestone-painting-take-one/

I'll try out the hitting the foam with a stone thing

In the photo it looks like texture isn't the problem. You could try increasing the contrast between your base color and your drybush or you could add a 3rd step by using a wash to give the texture definition.

For speed I recommend a wash.

I also like the idea of lightly sanding first to break up the surface of the foam and then using your stamp, but from the photos I'd say it was a paint/color issue not one of surface preparation.

(I've never gotten the rock technique to work except on balsa foam. But it could just be me not doing it right.)

one was sprayed with a texture spray but I dont think were gona be using that on all the pieces, the other piece is just painted... we were thinking of how we can make it look similar to the other without having to buy tons for textured spray...

if you push a rock against styrofoam you get impressions that are rough and natural looking.

if youre creating a cliff face ues a soldering iron. works great.

aviod the fumes, though.