Plaster of Paris

Plaster of Paris is a quick-setting gypsum plaster made of fine white powder (calcium sulphate hemihydrate) that hardens when wet and left to dry. Plaster of Paris, known since ancient times, is so named due to its production from the plentiful gypsum found in Paris.

When dry, the plaster of Paris does not shrink or fracture, making it an excellent material for casting moulds. It is often used to create and hold decorative plasterwork on ceilings and cornices. It’s also used in medicine to produce plaster casts to keep broken bones immobilized while they recover, however many current orthopaedic casts are composed of fibreglass or thermoplastics.

Plaster of Paris Formula

Plaster of Paris is also known as Calcium Sulphate Hemihydrate. The chemical formula of Plaster of Paris is CaSO₄.1/2H₂O.

Preparation of Plaster of Paris

Plaster of Paris is (POP) prepared from the chemical compound, calcium sulfate dihydrate, which is also known as, gypsum. Gypsum is represented by the chemical formula CaSO₄.2H₂O. POP is manufactured by heating the element gypsum at a very high temperature of about 373 K. When this happens at such a high-temperature value of 373 K, approximately three-fourths of its water of crystallization is lost, forming POP.

CaSO₄ · 2H₂O + Heat ⇢ CaSO4 · 1/2 H₂O + 3/2 H₂O (Discharged as steam)

Since the presence of moisture may slow down the setting of plaster by bringing about the hydration process. Therefore, it is stored in moisture-proof containers.

Properties of Plaster of Paris

Plaster of Paris exhibits the following properties,

• Plaster of Paris is a white-coloured powder, that forms crystals of gypsum when mixed with water.
• It forms an anhydrous calcium sulphate on heating at 473 K. 
• It expands slowly and slightly upon setting.
• It does not cause cracking of surfaces.
• It gives a decorative interior finish.

Uses of Plaster of Paris

Plaster of Paris founds its usage in the following areas,

• 3D Printing: Gypsum plaster can be used for 3D Printing. The water is applied by the inkjet head.
• Architecture and Decorations: Plaster of Paris is used to produce fine artwork to decorate and beautify monuments and buildings. It is also used to imitate wood or stone which is found in ancient buildings and monuments.
• During Burial Services: Plaster of Paris is used by executives of funeral houses in order to remake the damaged tissues and fill up the wounds.
• Medicines: It is used as a mould and cast. It is used to heal broken bones and cast into a supportive coating known as an orthopaedic cast.
• Fireproofing and fire protection systems.

Plaster of Paris, Baking Soda and Washing Soda are a few compounds which are widely used in our daily life. Sodium bicarbonate commonly known as baking soda is a chemical compound with the formula NaHCO₃. Sodium carbonate commonly known as washing soda is a chemical compound with the formula Na₂CO₃. Calcium Sulphate Hemihydrate commonly known as Plaster of Paris is a chemical compound with the formula CaSO₄.1/2H₂O.

In this article, we will learn about Plaster of Paris, Baking Soda and Washing Soda, its preparation, properties, and uses in detail.