Plaster of Paris is a Calcium sulfate semi-hydrate (CaSO4,½ H2O) derived from Gypsum, a calcium sulfate di-hydrate (CaSO4, 2H2O), by firing this mineral at relatively low temperature and thus reducing it to powder.
CaSO4, 2H2O + HEAT -------> CaSO4, 1/2 H2O + 1.5 H2O
In 1700’s, Paris was already the “Capital of plaster” since all the walls of wooden houses were covered with plaster, as a protection against fire. The King of France enforced rule after the big fire in England 1666.
Items Needed
(Apparatus) to make plaster of paris with glue
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2 parts Diluted White Glue
- 1 part Warm Water
- Large Mixing Bowl
- Spatula or Wooden Spoon
- Gather all the materials and spread a sheet on the work surface.
- Now, pour the glue in the large mixing bowl and beat it well.
- Make a paste, by adding one part warm water to two parts of white glue.
- Mix the ingredients well. Continue stirring them, until there no visible lumps remain.
- If you do not get a soupy mixture, you can add more water to the bowl and mix well.
- The final product should be watery, but with a slight white glue consistency.
Properties of Plaster Of Paris
- It is fine hygroscopic white powder
- Its melting point is 1630C
- Its density is 2.63 g/cm3
- It sets quickly on mixing with water giving out heat
- Expands slightly on setting
USES of Plaster of Paris
- Because of its property of slight expansion on setting, it is used for filling cracks and holes in plaster
- It is also used for filling cracks and knots in wooden surface before painting polishing
- Plaster of Paris is used in making surgical bandages where movable parts of the body are to be held rigidly in place
- It is used in chalk
- As plaster of Paris has high melting point, it is used for plastering the walls of wooden houses, such as a protection against fire
- It is used for making models and statues.
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