I'm planning a medium sized shelf diorama incorporating some small Joe playsets. It is basically going to be a mountainside outpost. I'm planning to use some craft styrofoam for the base shapes and then to sculpt over it to give it the rocky texture. What I'm not sure about is what kind of material to use to sculpt the texture. I was originally thinking of sheetrock joint compound but I'm not sure if there is anything better.

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Paper mache or cellulose clay both work well. You can also take newspapers and tear them into strips, then dunk them into a mix of Elmer's glue and water to apply over the styrofoam to help bulk it up and give it some shape.

check out how joemichaels did his arctic piece using styrofoam. I wouldn't sculpt over it at all, I'd build stacks of foam up (more like the insulation type of foam), then carve down from that, rather than use something else to build up from it.

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If you can live with a slightly smoother surface, then there's another way to go with it that's a little less labor-intensive and about a zillion times more durable: once you've got the sculpted piece ready to roll, you can take it to a place that does spray-on bed-liners for trucks and have them put a coat or two on it. I've used this for some carved-foam pieces for work purposes, and it works great: extraordinarily durable (the final product is nearly unbreakable) and holds paint pretty well. It'll retain the nooks and crannies of the piece, but it will dull the edges a bit.

Haveyou tried this or do you think it would work?

The aerosol will likely melt your foam. If you try amythin out of a spray can you should seal the foam beforehand with latex paint or something. Joint compound works well for adding texture so does wood putty. Or try a stone textured spray 8.

The model train guys will usually put something over the foam, to be more durable. Hydrocal plaster or some thing called Sculptamold being the preffered materials. They'll use it over shell based scenery, too. Paper mache would probably be fine. I bought some of Aves Studio's Master Mache, but I've yet to actually use it.

Whatever you use, tint it the same color you're planning to paint it. That way, if it gets chipped, you won't have stark white chips taunting you.

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I used joint compound for this:

Worked just fine.

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There's a "rocky texture" spray paint I've seen at the hobby stores, but maybe it would melt the foam too.

You can spray once the spackle is down. That's what I did on my volcano there. The rocky texture spraypaint is usually kind of low quality, though.

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