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?