How Long Does Plaster of Paris Take to Dry?
Most types of plaster of Paris set after 20 to 30 minutes. Some types, such as Herculite Number 2, set faster, in 8 to 12 minutes. Other types, such as Hydrocal FGR95, can take over an hour to solidify.
Setting times can be delayed 10 to 15 minutes by adding a few drops of lemon juice to the mixture. Using hot water to prepare the mix will accelerate the setting time. Plaster of Paris is a powder made out of gypsum. When it is mixed with water, it undergoes a chemical reaction that produces heat and turns the mixture into a solid.