I think the majority of rough handling comes from transporting the pieces from place to place. The bigger the piece, the more weight it has, and this magnifies the damage even if dropped from a few inches. I was using something called Durhams Rock Hard Water Putty when I first got my molds, and it is just marginally stronger than plaster of paris. While working on a small project, I dropped a pair of scissors on it and it broke off a piece. I now use Hydrostone and it is great. It will still break, but it takes much more force to damage it.