What Is Plaster?

Plaster is one of those words that you hear associated with construction and remodeling but have you ever asked yourself, what is plaster?

We’re here to help you find out. We’ll look at the different types and what they are used for as well as comparing plaster to drywall. 

What Is Plaster

What Is Plaster?

Plaster is a kind of building material that is used as a decorative finish. It has been in use for centuries in homes and in art. Today it is made from gypsum, a type of sedimentary rock but in the past it was made from lime or cement. 

In common usage plaster refers to a material that is used internally in a building while render is the term used to describe it when it is used externally 

Another term for plaster used for decorative purposes is stucco, but this isn’t used as an everyday finish to internal walls. Instead it is used to make decorative reliefs rather than as a flat surface finish. 

Types Of Plaster

There are three different types of plaster, each made from a different material. Lime, cement and gypsum plaster. 


Lime plaster is made from water, sand and lime. The kind of lime that is typically used is non-hydraulic hydrated lime which is also known as slaked lime. 

When this kind of plaster was used years ago the makers added horse hair as a binding agent and additives such as volcanic ash to reduce the working time of the plaster. 


Cement plaster is a mixture of water, Portland cement and sand. It is used both internally and externally. When used on internal walls it is finished with a coat of gypsum plaster. 

The thickness of plaster required will determine whether one or two coats are applied. 


Modern plaster is made with gypsum or calcium sulfate dihydrate. It is made by mixing gypsum powder with water and the resulting mixture is applied to internal walls and ceilings. 

Gypsum plaster is also used in the making of decorative moldings, ceiling roses and cornices. In medicine gypsum plaster is used to make casts for broken limbs. This is more commonly known as plaster of Paris due to its original gypsum extraction site. 

Uses Of Plaster

There are many uses for gypsum plaster including decorative and protective finishes to internal walls and ceilings, moldings, artistic uses and in healthcare. 

Decorative Finish 

The main use of gypsum plaster is as a decorative finish to walls and ceilings prior to painting. It creates a smooth surface that also serves as noise and thermal insulation. 


A lot of decorative moldings are made from gypsum plaster including cornices and ceiling roses. This is reminiscent of stucco plastering from previous ages and is not as popular these days as it once was. 


Plaster is also used in art to create statues and busts as well as intricate ceiling and wall decorations in churches and large homes. 


As a support and protection for broken bones plaster of Paris is used as a cast. Plaster of Paris got its name from the large deposit of gypsum that it originally came from the north of Paris. 

Difference Between Plaster & Drywall

Difference Between Plaster & Drywall

So what is the difference between plaster and drywall and do they both do the same job? 


Plaster starts as a powder that is mixed with water to form a consistency that can be applied to the walls with hand tools. However it needs a structure to be applied to and this is called lath. Previously, this was thin strips of wood that formed a matrix to support the plaster mix. 

Recently metal lath has replaced these strips of wood. When the first coat of plaster is applied to the wall it is scratched and then left to dry. 

Scratching involves scoring the still moist plaster with a serrated edge tool to provide a key for the following coat. This coat is then applied and left to dry, it is not scratched but has a slightly rough texture to it. 

Finally, a finishing coat is applied to the wall and as this is the surface that will be decorated the result should be smooth and even. 

Due to the number of coats, a plaster wall tends to be thicker than its drywall alternative. This provides more soundproofing, thermal insulation and passive fire resistance. 

As plaster is applied as a paste it is a good choice for irregular or curved surfaces. 

On the other hand, plastering is a time consuming and labor intensive job. This can result in high prices and long drying times between coats. Plaster can also crack as a house moves or settles over time. 


Unlike plaster, drywall is a solid sheet of material that is ready to be attached to the wall. It has two faces, one is smooth, and the other has a rougher texture. 

The drywall sheets are attached to the framing of the house with drywall screws and where necessary are cut to fit. Corner beading is installed to give a straight edge and the joins are covered with paper joint tape. 

Two or three layers of joint compound is then applied to the joins between the drywall sheets as well as over the screw holes. Each coat is lightly sanded before the next coat is added. Once the third coat has dried the drywall is ready to be painted. 

The obvious advantage of drywall over plaster is that it is much quicker to put up and can be done successfully by DIYers. Plastering is a skilled trade. 

However, like plaster, drywall can be affected by structural movement and is prone to damage from impact. 

Final Thoughts

Plaster has been around for many centuries and is still a commonly used building material. 

There are many advantages to using it for internal walls and ceilings while it is also used for decorative and medical purposes. 

We hope you have enjoyed this guide to plaster and that it has been helpful. 

Joel Adams
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