Lightweight Hydrocal plaster is great stuff for molding your own rocks and brick walls saving a lot of time and money while making custom pieces. Very easy to mix and pour. Gives off a little heat while curing. I carve or sand mine if needed before it is fully cured. Easy to attach to existing terrain with a hot glue gun. But I have found through experience that you will need to seal the back of the rock sections with something like an acrylic glue, white glue of Mod Podge so that you seal the surface and the hot glue holds.