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Name: Damian
Status: Student
Grade: 9-12
Location: FL
Country: USA
Date: July 2006

What additive that will slow the reaction of hardening Plaster of Paris, after water has been added to the powder?

Hi Damian,

Interesting question, and not one often asked! The hydration reaction that results in the hardening of Plaster of Paris proceeds very rapidly as your question infers. This reaction can be slowed somewhat by the addition of several common organic acids. Tartaric and citric acids (tartaric acid in particular) have been used for this purpose, and are known as "retarders".


Bob Wilson.

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