How long does a POP cast take to set?

A Plaster of Paris cast begins setting within 10 to 15 minutes and becomes fully hard in about 30 to 45 minutes under normal room conditions. The setting time depends on temperature, humidity, and water ratio. Warmer environments or less water speed up setting, while cooler or humid conditions slow it. The chemical reaction converts calcium sulfate hemihydrate back into gypsum, releasing heat as it solidifies. 

Though the cast feels firm after half an hour, it’s best to let it dry completely for 24 - 48 hours before painting or sanding. Rapid drying using high heat can cause cracks, so air drying is preferred. For artistic or construction projects, additives such as glue or retarders can adjust the setting time. In summary, initial hardening happens quickly, but full strength and dryness require at least one to two days of curing.