Well, the foam is only used to make the stones, and if I put chicken wire over it, I'd lose the stones. I wanted just a bit of depth which is why I used the foam in the first place (instead of just painting on stones).
I didn't even try sanding because I just didn't have the time, however, I imagine the same results. The foam, besides being porous is very soft, which is the real reason it chips so easily -- the mud makes a 'solid' layer, but if you accidentally touch it or push it, the foam gives out and causes the cracks.
I tried taking some of my stryofoam sheeting and cutting it to size (both length, width, and depth), and the monster mud stuck fine without cracking, BUT, the foam was too tough and rigid that it didn't conform to the roundness of the wall.
Basically, I'm just saying if anyone tries something similar, to do a test run on whatever material you use.
You wouldn't happen to have any air compressors for sale in your store wouldja'?
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