What is Plaster of Paris

Plaster of Paris is basically a building material that consists of a fine, white-colored powder, known as calcium sulfate hemihydrate. The term 'plaster' encompasses plaster of Paris, lime plaster and cement plaster. Plaster of Paris was believed to be used since ancient times; the oldest traces were found in Anatolia and Syria and estimated to be about 9000 years old. The Egyptians, Greeks and Romans used plaster of Paris for sculpting their tombs and other monuments, as well as in buildings for fireproofing.

Plaster of Paris is obtained by heating gypsum or calcium sulfate dihydrate to about 140 - 180°C. When gypsum is heated to such a temperature, it loses three-quarters of its water content, leading to the formation of plaster of Paris. The process of making plaster of Paris is reversible; meaning that if the dry plaster powder is mixed with water, it re-forms into gypsum. The name plaster of Paris is derived from the large deposits of gypsum in the Montmartre hill in Paris.

Plaster of Paris is more or less similar to other building materials like mortar and cement; a paste can be made by adding water, which liberates heat and eventually hardens. When plaster of Paris is mixed with water molecules, there is hydrogen bonding between the calcium and sulfate ions. This is the reason as to why, the resulting plaster is soft and smooth. While using for a specific purpose, plaster of Paris paste is molded into a desired shape before it hardens. A major advantage of plaster of Paris is that there is no volume loss after drying. Hence, the mold and cast are of the same size.

As plaster of Paris remains soft (to some extent) even after drying, it can be easily manipulated by using sandpaper or metal. That's why it is used for construction purposes, either by mixing with other substances or as a finishing material. However, plaster of Paris is widely used in home decors; various designs can be made in the walls and ceilings. For many modern sculptors, it is a favorite sculpting material, mainly because of its easy occurrence and speed of setting. In addition to arts and architecture, plaster of Paris is also used in orthopedics to make smooth casts for broken limbs. In forensic science, molds of foot prints and other important markings are made by using plaster of Paris for further investigation.

The properties of plaster of Paris can be studied with the help of homemade plaster of Paris. This can be a good project for preschool and elementary students. You can try preparing a type of plaster of Paris by many methods. The most easy ones are, creating plaster of Paris either with white glue or flour. In the former case, prepare a paste of white glue and warm water. Make sure to add warm water gently by stirring continuously; stop adding water when the mixture turns into a paste form. Your homemade plaster of Paris is ready, you can create certain designs out of it. In the flour method, prepare a homemade plaster of Paris by mixing white flour and water. You can make masks, mobiles and bubble paint from these homemade plaster of Paris.