What Is A Plaster Of Paris?

What Is A Plaster Of Paris?

What Is A Plaster Of Paris?

Plaster of Paris also known as Gypsum plaster is a white powdery chemical compound made from heating gypsum at a high temperature. It is commonly used for sculpting materials and in gauze bandages. Its chemical formula is CaSO4·1/2H2O.

Plaster of Paris must be kept in airtight containers to prevent the absorption of moisture, as this can cause the material to hydrate and become unusable.

When mixed with water, the plaster powder rehydrates into gypsum and sets within 45 minutes, accompanied by a small increase in volume. It is commonly used for creating casts and sculptures. Over time, the plaster becomes harder and stronger as it transforms into interlocking crystals.

Heating the plaster at high temperatures results in the formation of different forms, such as hemihydrate and anhydrite, which can also rehydrate when exposed to water and have industrial uses like desiccant.

Why Is It Called Plaster Of Paris?

Plaster of Paris has been in use since ancient times, with the earliest known production dating back to 9000 years ago.

It was used by various ancient civilizations such as the Greeks, Egyptians, and Romans. However, large-scale use of plaster became prevalent in the 18th century when it was mandated for use in all construction in Paris following a devastating fire in London in 1666.

This led to increased gypsum mining in the Paris area, making it a major center for plaster production, hence the name “Plaster of Paris.”

Properties Of Plaster Of Paris

Plaster of Paris is a fine powder made from gypsum that is mixed with water to form a paste, which then hardens. It is commonly used for casting and molding in arts and crafts, as well as for plastering walls and ceilings. Some properties of Plaster of Paris include:

  • White in color and available in powder form
  • Becomes solid when mixed with water
  • Exothermic setting process, which can be accelerated or slowed with the addition of other chemicals
  • Forms anhydrous calcium sulfate at high temperatures
  • Can be shaped and worked with various tools, but has relatively low strength and may require external support.

Is Plaster Of Paris Waterproof?

Plaster is not naturally waterproof, but it can be made waterproof by mixing it with other materials. It is a dry and porous substance that absorbs water when exposed to it.

To make it waterproof a heavy-duty primer can be applied, followed by a heavy-duty exterior paint or other paint.

Alternatively a coat of linseed oil can be applied after lightly sanding the plaster surface for better absorption. Different waterproofing methods and techniques are used depending on the specific situation.

Is Plaster Of Paris Dangerous?

Plaster of Paris is a calcium sulfate hemihydrate that may contain silica and asbestos impurities. If not handled properly, it can be dangerous and lead to permanent lung damage and other health problems. It is commonly used in arts and crafts, but it is important to take safety precautions such as wearing a mask to prevent inhaling the powder, wearing gloves to avoid skin contact, and disposing of it properly to prevent pipe clogging. If used carefully, it can be a fun and creative material.

Uses Of Plaster Of Paris

Plaster of Paris is a versatile material with a wide range of uses and applications in various sectors such as building and construction, decoration, arts and crafts, medicine, and dentistry. Some of its uses include:

Building material: Constructors and architects use it as a protective coating on walls and ceilings before painting and for fire-proofing.

Moulding and casting agent: It is used to make statues, showpieces and other decorative elements.

Medical applications: It is used to create casts for bone fractures and immobilization shells for radiotherapy patients.

Decoration element: It is used to make decorative pieces and can be used creatively on walls for patterns and designs.

Art and crafts: It is used for various art and craft purposes by both children and adults, as well as by artists and painters.

Dentistry: Dental clinics use it to make moulds and casts of teeth for temporary purposes, replicas of teeth and tissues, and wax false teeth.

Fireproofing: Its fire-resistant properties make it useful in buildings, fireproofing products and fire protection systems.

What Are The Types Of Plaster Of Paris?

There are three main types of plaster that are commonly used. They are:

Gypsum plaster, which is made by heating gypsum to 300 degrees Fahrenheit. If it is heated above 392 degrees Fahrenheit, it becomes anhydrite. When water is added to gypsum plaster powder or anhydrite, it turns into gypsum.

Lime plaster, which is a mixture of sand, calcium hydroxide, and other fillers. It is made by heating limestone to create quick lime and then adding water to make slaked lime, also known as white powder or wet putty.

Cement plaster, which is a mixture of plaster, Portland cement, sand, and water. It is applied to both exteriors and interiors to achieve a smooth surface and is often topped with a final layer of gypsum plaster.


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