SURFACE ROCK MOLD - Ready-Made Woodland Scenics Rock Molds are durable, flexible and well detailed. The 15 selections offer value and versatility not available anywhere else. Cast small molds, rock outcroppings, top rocks, or entire rock faces. Lightweight hydrocal castings release easily and completely. UltraCal 30 Hydrocal is recommended; however, Plaster of Paris may be substituted. Tip: 'Wet Water' solution release: 1 quart water and 2-3 teaspoons dish soap. (We like Ivory).