At some time or another all of us will get the urge to make some rocks out of polystyrene or a similar foam material. Of course we all know what rocks look like so it should be simple to just cut something into a rock shape and paint it. Except it doesn’t look right, does it.
The problem with cutting foam is that although it might have a rock shape it doesn’t have a rocks texture. Now you could just paint it with a course filler (or a fine filler mixed with some sand) but this is still not that convincing.
Luckily the solution is simple. Take a trip out to your garden or the local park and find a stone with a rough texture. Now simply push this into the surface of your carved foam rock, varying the angle and pressure as you work your way around the surface. Once painted this will give you a far more realistic texture to your rock and it won’t look as contrived as if you simply tried to model it with extra detail yourself.
This technique also works well for stone paths, cliff faces and anything else where a rough surface is required (you can even use it to texture Greenstuff instead of foam).