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Plaster of Paris (POP)

Plaster of Paris (POP) is a building material having Gypsum, which is a naturally occurring crystal of calcium sulphate (CaSO4.2H2O). Chemically, Plaster of Paris is calcium sulphate having molecular formula CaSo4½H2O. It is a white hygroscopic powder very slightly soluble in water particularly at high temperature. It is used for coating walls and ceilings and also for creating architectural designs. Plaster of Paris is manufactured as a dry powder and is mixed with water to form a paste when used. Plaster of paris does not generally shrink or crack when dry, making it an excellent medium for casting molds. Plaster is most suitable for application of internal plastering system as punning of walls and ceilings, all decorative works like cornices, roses, moldings, arches apart from in-situ false ceiling systems.

Plaster of Paris is prepared by heating calcium sulfate dihydrate, or gypsum, to 120–180 °C (248–356 °F). With an additive to retard the set, it is called wall, or hard wall, plaster, which can provide passive fire protection for interior surfaces.

Below are some of its advantages and disadvantages to give you an idea whether you should use it in your dream home or not.

Advantages of Plaster of Paris:

  1. It has good adhesion on fibrous materials. Gypsum plaster is directly applied on brick, block or RCC, no separate finishing product required. It requires no curing, therefore ready to paint.
  2. It has no appreciable chemical action on paint and does not cause alkali attack.
  3. It is light in weight and more durable.
  4. It has low thermal conductivity.
  5. It is very good fire resistant and hence a very good heat insulating material.
  6. Gypsum plaster expands slightly on setting and is not, therefore likely to cause cracking of surface
  7. It forms a thick surface to resist normal knocks after drying.
  8. It mixes up easily with water and is easy to spread and level.
  9. Plaster of Paris gives a decorative interior finish. Its gypsum content provides it a lot of shine and smoothness.
  10. It can easily be moulded into any shape.

Disadvantages of Plaster of Paris:

  1. Gypsum plaster is not suitable for exterior finish as it is slightly soluble in water.
  2. Gypsum plaster is more expensive than cement sand plaster but cost disadvantages should be weighed against the advantages and the fact that the labor cost is appreciably greater than that of materials in plastering.
  3. It cannot be used in moist situations.
  4. Skilled labour is required for precise application and thus labour cost for applying plaster of Paris is high.

Preparing & Mixing Plaster of Paris is easy but there are important steps to keep in mind while using.

  • Plaster of Paris powder
  • Water
  • Mixing container
  • Spoon or spatula
  • Measuring cup
  • Newspapers or plastic mat

Cover your work area with a plastic mat or with newspapers. Find a mixing container (preferably a disposable one) that could accommodate the amount of mixture intended.

The ideal ratio for a Plaster of Paris mixture is 2 parts Plaster of Paris powder to 1 part water. Measure out the water and pour it into your mixing container.

Start adding the Plaster of Paris powder to the water in your mixing container by sprinkling or sifting the powder over the water. Do not add the powder in one spot, instead try to cover as much area as you can.

Gently mix the Plaster of Paris mixture until it reaches a uniform and smooth consistency. Do not stir vigorously to avoid any air bubbles from forming.Allow the mixture to stand for a minute before start the work.

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