Plaster of Paris

Plaster of Paris | Uses, Types, Formula

This article will throw light on the origin of the plaster of Paris and its uses. It also shares information about the chemical composition of P.O.P and its different types.

Also, we have discussed the characteristics of plaster, its formation process, and more. Let us talk about all of it one by one.


What is the Plaster of Paris?

Plaster of Paris is a white colored powder used in sculpting, casting, 3D printing, Medicine, etc.

It is made up of Gypsum and chemically it is called Calcium Sulphate Hemihydrates which is obtained from heating gypsum.

Properties of Plaster Of Paris

* It is in fine powdered form and is white in color.

* When mixed with water, it becomes a thick paste that can be molded into any desired shape.

* After the moisture evaporates and plaster dries, it retains the formed shape and becomes hard mass.

* It has an exothermic setting process.

* When the plaster of Paris is set its volume expands a bit making it heavy than before.

* It is always stored in a moisture-proof container because moisture can cause a slow setting of plaster of Paris which will make it useless.

* When heated at 473K, it forms anhydrous calcium sulfate which is called dead burnt plaster of Paris.

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Why it is called Plaster of Paris?

It has been known to people since ancient times. The very first traces of plaster of Paris fall around 9000 years ago and were used by ancient Greeks, Egyptians, and Roman Civilization.

The name ‘Plaster of Paris’ came from the fact that it was made by heating gypsum which was mainly found in Paris. Montmartre in Paris had large deposits of Gypsum which was heated to get this plaster.

However, it got people’s attention when it was used in all the constructions in Paris.

The incident of a fire breaking down in 1666 in London led the King of France to take this decision of covering all wooden walls with the Plaster of Paris to avoid any accidents in the future. As a result, large-scale gypsum mining was carried out in Paris and it became the center of plaster production by the 18th century making it known as Plaster of Paris.


Chemical Composition

CaSO4 ◦ 2H2O is its chemical formula.

Formation of Plaster of Paris

Plaster of Paris is manufactured by heating gypsum in rotary kilns at 120-180º C. It gets partially dehydrated.

When gypsum gets heated at such a high temperature, it starts losing its water molecules and turns into calcium sulfate hemihydrates. This is when it is called the Plaster of Paris.

When water is added to the powder, the hardening process starts around 10 minutes after blending the paste and takes 45 minutes to get dried completely.

Uses of Plaster Of Paris

Plaster of Paris is used in plenty of places across several sectors. We have listed a few of its major areas where its use has been witnessed heavily.

Building Material

The plaster of Paris is vastly used in construction areas. It is used as a building material by architects and constructors.

It is widely used as a protective coating on walls and ceilings before the application of paint. It offers a smooth application of paint and serves as a fireproofing barrier as well.

Moulding and Casting Agent

It can be used to create the molds of the design so that the mold works as a “negative” to make multiple models of the same design.

Such molds of plaster of Paris can be used to make clay objects which when heated in fire turn out as terracotta decorations.

Several statues, showpieces, and decorative items are made using Plaster of Paris because it is comparatively inexpensive than other methods.

Medical Applications

Plaster of Paris is widely used as a supporting element in bone fractures of humans. It is used in the orthopedic cast to provide support to the broken limb.


Here Plaster of Paris is used to fabricate the immobilized shells for patients. Plaster bandages are used to create impressions of the patient’s head and neck.

The plaster paste is used to fill the impression and create a dummy that will hold the patient’s head steady while the radiation is being delivered.


The plaster of Paris is used to create molds and casts for oral tissues. The working models of dentures (false teeth) are made up of dental stone which is a stronger material than plaster and is manufactured from gypsum under pressure.

The plaster can withstand the high heat and pressure needed to ensure a rigid base for strong dentures.

Fire Protection

The plaster of Paris releases water vapor when exposed to fire. It slows down the process of fire spreading by one to two hours. Alongside it slows down the heat transfer into steel elements preventing the fire breakdown effectively.

Hence it has been majorly used in fireproofing materials. And it is used to coat objects so that they don’t get exposed to fire that easily. 


Plaster of Paris is used to create beautiful decorative items. It is used heavily in creating idols of Ganesha for the Ganesh Chaturthi festival and the idols of Durga during Dussera.

It is used on walls and ceilings to create mesmerizing patterns and designs that enhance the aesthetics of the place.

Plaster of Paris has been used in making false ceiling, beautifying pillars, and walls before painting.

Art & Craft

Plaster of Paris is heavily used by children and adults for sculpting and learning to make sculptures.

It is used in the art sector based on the need for applicability of the material.

3D Printing

Nowadays Plaster of Paris is heavily used in 3D printing where water is specifically applied by inkjet head.

Burial Services

Several funeral places use Plaster of Paris to rejoin the limbs of the dead or to fill out the cuts and bruises occurred during accidents to remake the damaged tissues.

Types Of Plaster

There are 5 types of plaster that are discussed below. Let us see each one of them one by one.

Clay Plaster

Clay plaster is a mixture of sand, water, and clay. It is the first of its kind that has been used in building houses since the times of the American colony’s settlements.

Clay is an earthy material and contains a variable amount of water that turns it into plastic when wet. It has hydrated silicates of aluminum.

Clay is used to making bricks, pottery, coating walls, etc.

Straw or dried grass is added to the mixture of clay, water, and sand to give it a strong tensile strength. This mixture acts as a protein adhesive that works well as a binding material.

The clay plaster should be dried properly after coating it in required places or after making the designs to get the desired strength out of it.

Clay plasters because of their lack of tensile and compressive strength soon were replaced by other alternatives like lime and gypsum as they had binding qualities that were desired in the architecture sector.

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Gypsum Plaster

Gypsum plaster or plaster of Paris is prepared by heating gypsum in the kiln at a temperature of 180ºC. Also if it gets heated above that temperature it turns into burnt gypsum or anhydrite.

We have already discussed all the properties of this plaster above.

Lime Plaster

Lime plaster is a mixture of calcium hydroxide and sand. The carbon dioxide from the atmosphere transforms the calcium hydroxide into limestone (calcium carbonate).

Lime plaster is made by heating limestone above 850 ºC to produce quick lime (calcium oxide). After this water is added to it to make calcium hydroxide which is then sold as wall putty or white powder.

Water is then added to this white powder that creates a thick paste to be ready to use. If the paste is exposed to air for a longer time it turns grey because of carbon dioxide and the paste slowly starts getting hard.

This plaster is also resistant to fire. Therefore its coating is used on walls to eliminate any unwanted events during fire breakdown.

Cement Plaster

 The mixture of suitable plaster, cement, sand, and water forms the cement plaster. It is most widely used in masonry work while making houses or buildings during the foundation processes.

It is used in between the bricks to provide strength and binding to the walls of the houses.

It is also applied to the exteriors and interiors to obtain a smooth finish. On top of it, the interiors sometimes receive a fine layer of gypsum plaster as well.

It was first introduced in America in 1909 and was popularly known by the name Adamant Plaster. Adamant was a great manufacturer of those times.

Heat Resistant Plasters

Heat resistant plasters are used for coating walls and chimneys and can be used as fire barriers. They replace gypsum plasters in the places where the temperature gets too high for gypsum plaster to stay on the wall.

Safety Concerns While Using Plaster Of Paris

There is an exothermic reaction that occurs when the plaster of Paris is mixed with water. When the plaster sets it can reach up to a temperature of 60 ºC and if it is in large quantity then it may also cause burns on the skin.

Other variations of plaster containing silica and asbestos are harmful to inhale. They have carcinogens that can even cause cancer.

People working regularly with these plasters should take optimum precautions as they may have negative effects on their health.

The manufacturing units and raw material factories expose their workers daily to these hazardous materials as workers may breathe these materials, swallow them accidentally, or maybe in direct contact with them.

There are some industrial precautions that should not be ignored at any cost. And people who are using such materials for craft and creativity should also take all the necessary precautions to avoid any accidents in the future.

Alternatives To Plaster of Paris

Materials such as softwood, limestone, granite, casting clay, wax, and other such products can be great alternatives to plaster of Paris.


Eco-friendly products simply mean those items that do not impose any harm to the environment and do not contribute to the existing greenhouses gases that are degrading the earth in multiple manners.

The plaster of Paris is not an eco-friendly material as it takes a lot of time or years to decompose and thus it harms the environment.

Final Words

Plaster of Paris has widespread use in multiple sectors from construction to medicine to decorations to bindings to fireproofing. It is used almost everywhere in current times.

This substance has been the first choice for the makers as it is very economical and is available in abundance from the mining of gypsum. But there are many more factors that should be considered now and are the problems of the present.

Plaster of Paris adds to global warming and is not an eco-friendly material. In present times, we are struggling to maintain the temperature of the earth and not lead to global warming.

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The substances like plaster of Paris and other materials are contributing to these global tensions.

So we recommend our users to think before using such materials and save the environment. We hope this reading was helpful to our reader and was able to answer your queries. We have tried to cover every detail related to this topic and provide the desired information to you.

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