Sandtastik PLASTERMIX Plaster of Paris Casting Compound. It is fun to mix-and-make your own plaster casting creations. Much like plaster of paris, this wonderous arts and crafts compound is simply mixed with half a part, then poured into shapes, water molds, etc. Sandtastik PLASTERMIX sets in just 20-30 minutes. Once dry, your keepsake ornaments are ready to decorate.