Page 30 - Curriculum Visions Dynamic Book

Calcium sulphate
Plaster is made of another important compound of calcium, calcium sulphate.
The material used to make plaster occurs naturally as a soft white rock known as gypsum. It can be made into a fine form and used as a crack filler or poured into molds to make plaster figures. This material is called Plaster of Paris.
Where gypsum is found
Gypsum is found in thick beds, often in the same place as rock salt. This is because gypsum was formed by the evaporation of sea water
in ancient seas. It is still being formed in some inland salt lakes, like Australia’s Lake Eyre and Utah’s Great Salt Lake. Gypsum is cheap to quarry and so is a good material to use in house building, where large amounts of inexpensive materials are needed.
Uses of plaster
Because gypsum is easy to make into a paste and will set hard as it dries, it is used throughout the world as wallboard. The gypsum is put in shallow molds and then covered with a sheet of strong paper. This stops the gypsum board breaking as it is carried about.
Gypsum wallboards are soft and easy
to cut into shapes. They also give the very smooth finish that we expect of the walls in our rooms.
 Plaster (gypsum and water made into a paste) can be applied with a trowel to finish off a wall. The main wall surfaces are gypsum too, in the form of prefabricated wallboard.
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