Ancient Egyptians Used Plaster as a Building Material in Pyramids.
When you hear someone mention the term "plaster," they typically mean plaster of paris. It has a number of uses, from building to sculpture to casting to children's crafts. Plaster is made from powdered gypsum and water, which does not shrink and hardens quickly. Plaster has been used for centuries. The oldest evidence of plaster in use is 9,000 years ago in Syria.
Building
Once plaster has been mixed, it begins to harden quickly. This can prove problematic when plaster is being used as a facade material, as in stucco. Because of this, plaster used in facades is frequently mixed with a substance that delays hardening and toughens the plaster facade, such as powdered citric acid, marshmallow root, dextrin, gum arabic or glue. Before plaster can be applied to a facade, a bonding surface must be prepared. Frequently, a mesh screen, such as chicken wire, is attached to the facade to create a bonding surface.
Casting
Because of its fast hardening time, plaster of paris may be used for casting molds for sculpture and crime scene re-creation. When casts are made, the casting impression must first be coated with a release agent to prevent the plaster from sticking. Liquid soap, thin oil or soft clay are frequently used as release agents.
Sealing
When plaster has dried, it must be sealed to keep dirt from building up in its pores. Common sealing agents include shellac, linseed oil or wax. When sealing with shellac, two coats are normally required. Let your first coat of shellac dry completely before adding the second.
Patching Plaster
If your plaster develops bubbles, seal the bubbles by opening them with a fine-pointed steel tool and then filling the opening with a small amount of thin plaster mixed with excess water.
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