Plaster of Paris is a brand name for gypsum hemihydrate, which is a form of dehydrated gypsum rock powder. When water is added to the powder, the rock hardens again, forming a solid mould. You can recycle Plaster of Paris by dehydrating the plaster to make it revert to the powder state. When this occurs, the plaster can be remixed with water to mould the plaster into any desired shape or mould.
Preheat the oven to 163 degrees Celsius. Wrap the Plaster of Paris piece in an old towel and take it outside to eliminate mess. Wear a dust mask over your mouth and safety goggles to protect your eyes and mouth from dust particles.
Use the hammer and chisel to break the Plaster of Paris block into small pieces. Break the pieces into 1-inch chunks. Place the pieces into a disposable oven pan sometimes used for baking turkeys and roasts. Wash the towels in the washing machine to dispose of the dust particles.
Place the oven pan into the preheated oven. Allow the plaster pieces to dehydrate overnight. If you are not comfortable leaving the oven on all night, you can start the process in the morning and take out the plaster just before you go to bed. The heat from the oven will slowly evaporate the water from the plaster.
Take one chunk of plaster out of the oven the following morning. Crush it with a hammer to check for any remaining moisture. The plaster may need a few more hours to extract all of the moisture from the plaster. If the plaster crumbles into a fine powder, it is dry enough. Take the rest of the plaster pieces out of the oven and allow them to cool completely.
Place the pieces inside a grinder and grind them into a fine powder. The Plaster of Paris can be recycled for use in other projects or places. Simply add more water and remix to mould it into any desired shape.
Take care when grinding the plaster to not overheat the motor. If the grinder has trouble with the plaster, use a smaller amount in the machine.