False rock creation techniques
Here are some false rock techniques that one could consider. One of the things I did not realize is the importance of taking into consideration the size difference of your rock sculpture from when you began it compared to after it's finished.
The grout increases the size considerably with each layer that is applied. It of course will do this in every direction -bottom, top, left and right. After three or more layers you might potentially have a problem placing the sculpture back into it's cage.
With the first sculpture I did I did not think about this, and eventually had to take a knife and remove about a half an inch on one side of the false rock sculpture. This was discouraging because then I started to think what else am I forgetting? I guess we all learn by failing.
Another thing I've noticed is the enormous amount of white styrofoam balls all over the place after you've made just a simple cut into the polystyrene. An idea to avoid this might be to use a hot wire cutter made for cutting polystyrene. I've not used one yet but I've heard that the Tippy hot wire cutter is safe to use as long as you've got adequate ventilation.
There is absolutely no "mess" of small Styrofoam pieces littering the floor. As I said earlier I've not tried this product, but I am looking into it, as the messy side of this process is quite irritating.