Understanding
the UL Fire Resistance Directories
Calcination & Rehydration
Rocks are grounded into small pieces then
they are heated up
to approximately 350░ F. This
is were a chemical reaction called calcination
takes place.Gypsum
is composed of molecules of calcium sulphate and
water locked into a rigid crystalline structure. When gypsum
is heated, about 75% of the water is driven off as
steam. The resulting white powder is called stucco.
When
water is added to the stucco crystals reform and the
gypsum returns to its original hardness. This process is
called rehydration.
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