Plaster of Paris

What is Plaster of Paris (POP)?

Plaster of Paris, commonly abbreviated as POP, is a white powdery substance derived from gypsum, a rocklike mineral. When gypsum is heated to about 160-170°C, it loses water and transforms into the hemihydrate form known as POP.

What makes Plaster of Paris hard?

Plaster of Paris Hardens by adding water to it. When PoP is mixed with water it takes on the unique property of hardening into a solid mass. 

How Plaster of Paris is prepared?

Plaster of Paris is prepared from the chemical compound, calcium sulfate dihydrate, which is also known as, gypsum. Gypsum is represented by the chemical formula CaSO₄.2H₂O.

Why is Calcium Sulphate Hemihydrate called Plaster of Paris?

Calcium Sulphate Hemihydrate is called Plaster of Paris because of the fact that it is prepared from the chemical compound called gypsum which is found to be most abundant near Paris.

Is the Plaster of Paris considered to be eco-friendly?

No, Plaster of Paris (POP) is considered to be hazardous for the environment. It gets dissolved in the water and soil thus making it harmful. 

What happens when Pop is burnt above 250 °C?

When Plaster of Paris is burnt above 250 °C, a compound called β-anhydrite or dead burnt plaster is formed and it is a completely anhydrous product.

What is dead burnt plaster?

When the chemical compound of plaster of Paris CaSO₄ . 0.5 H₂O is heated above the temperature of 393 K, its water of crystallisation is lost and anhydrous Calcium sulphate is left as a residue which is known as a dead burnt plaster.

What are the main uses of Plaster of Paris?

Plaster of Paris is versatile, used in the medical field for making casts and molds, and in construction for decorative ceilings and fireproofing. Its ability to form a smooth, hard surface when mixed with water makes it ideal for creating intricate artistic and architectural designs​.

Is Plaster of Paris environmentally friendly?

While Plaster of Paris itself is derived from a natural mineral, the environmental impact largely depends on the mining and processing methods used. It is generally considered non-toxic but should be handled with care to avoid dust inhalation​.

Can Plaster of Paris be used outdoors?

Plaster of Paris is primarily recommended for indoor use as it is not water-resistant. Exposure to moisture can degrade its structure, leading to damage. For outdoor projects, other materials that withstand weather conditions are preferable​​.

How long does Plaster of Paris take to set?

Typically, Plaster of Paris sets within 30 to 45 minutes, and it is advisable to work quickly once it is mixed with water. It achieves a very hard finish upon drying, which can take up to 72 hours depending on the thickness and ambient conditions​.

Can Plaster of Paris be painted and sanded?

Yes, once fully cured, Plaster of Paris can be sanded to smooth out any imperfections and painted with most types of paint. This makes it a popular choice for craft and repair projects where a specific finish is desired​.

Plaster of Paris is a well-known chemical compound that is widely used in sculpting materials and gauze bandages. While we have seen numerous applications of this substance in our daily lives, Plaster of Paris is a white powdered chemical compound that is hydrated calcium sulphate that is typically produced by calcining gypsum. In other words, Plaster of Paris is often produced using heated gypsum at a high temperature.