Use this plaster additive to make a great plaster casting in ComposiMold or ImPRESSive Putty Molds. To use, add 4% Plaster Powder Additive to your Plaster of Paris or other plaster material. The addition of the Plaster Powder Additive cures the plaster faster on the outside to make a strong solid casting. By creating a faster cure, the water in the plaster does not react with the ComposiMold or ImPRESSive Putty so the final product is a strong, hard plaster casting.