Is Plaster of Paris Hard?

Plaster of Paris is a widely available material that is popular for making crafts. You can even make your own plaster of Paris at home using flour, water, and glue. This material can be used to make molds, casts, and other art projects. But is it a strong material? If not, how can you make it stronger? We will find out the answer below.

Is plaster of Paris hard? Plaster of Paris is a hard substance that is colored white. It is made by adding water to powdered and partly dehydrated gypsum. The plaster of Paris is hard like concrete or cement but is not as strong. Hence, it is not ideal to use it as a material for very thin castings.

Plaster of Paris is simple and easy to use so it is ideal for basic castings, molds, and art projects. It can set in just a few minutes, but it takes at least an hour before it can be removed from the mold. Moreover, it takes about 24 to 48 hours for a plaster of Paris casting to fully cure. Let us find out more about this material below.

Why is Plaster of Paris Hard?

It is believed that the hardening of the Plaster of Paris is because of rehydration as well as its reconversion into gypsum. Adding common salt into the mixture accelerates the setting rate. On the other hand, adding a little borax into the mixture reduces the setting rate.

How Hard is Plaster of Paris?

While plaster of Paris is a soft material, it can be very hard and strong when used in castings. On the scale of mineral hardness where talc is 1 and diamond is 10, the plaster of Paris is about a 2. Hard casts of plaster of Paris can be sanded, trimmed. And while it is hard, it is drill fragile and can get damaged easily.

Does Plaster of Paris Dry Hard?

The plaster of Paris gets very hard when it is dried. Mixing plaster of Paris powder with water makes it a great material for sculptures to casts. On the other hand, though it is hard, the basic plaster of Paris mixture is fragile when dry. To make it stronger, you can add glue into the plaster of Paris and water mixture.

What is Harder than Plaster of Paris?

Hydrocal is stronger and harder as compared to plaster of Paris. Aside from that, hydrocal also takes more detail and does not slough off when it is dry. You can also check out this article titled, can I mix white cement and plaster of Paris? We have shared an in-depth discussion about the topic.

Why Does Plaster of Paris Harden when Mixed with Water?

Plaster of Paris hardens when mixed with water because the water molecules recombine which allows the gypsum to harden again. Moreover, the plaster of Paris absorbs water and forms dihydrate. This sets and forms a hard unified mass. Take note that the plaster of Paris is not water-soluble and retains its form when exposed to water. We have also shared this article that discusses what happens if plaster of Paris gets wet. You can check out the article for useful tips and ideas that you can refer to when working with plaster of Paris.

How to Harden Plaster of Paris?

You can harden the plaster of Paris by adding glue to the mixture. Take note that the plaster and glue recipe is suitable for small casting projects only. Adding glue into the mixture makes plaster of Paris harder and durable enough so that it can be sanded using fine-grit sandpaper. On the other hand, you can also use the same recipe for making large projects. For more information about this topic, check out this article that discusses how to make plaster of Paris stronger.

Step 1 – Mix Water and Glue

The first step that you need to do to harden the plaster of Paris is to mix water and glue together. Pour 1 ¼ cup of water into a plastic container. Then, add ¼ cup of white glue into the water. Mix the water and glue until the glue is thoroughly dissolved into the water. You will know this if the water turns milky with a creamy consistency.

Step 2 – Add the Plaster of Paris

Once you have mixed water and glue, the next step is to add the plaster of Paris. Slowly pour 2 cups of plaster of Paris into the water and glue mixture. Make sure to add only a small amount of plaster at a time. Do not stir and let the plaster settle to the bottom. Stirring can produce air bubbles that can weaken the plaster.

Step 3 – Sit and Mix

Allow the plaster to sit for about five minutes into the water and flue mixture. After that, start mixing to create a slurry.

✅ Video – How to Mix Plaster of Paris | Technique the Easy Way for Superior Strength Tutorial

Environ Molds shared the video below on YouTube. It discusses how to mix plaster of Paris. In the video, the technique to have superior strength plaster of Paris is shown. The video shows the eight steps that are used to make high-quality plaster art castings that are durable. Check out the video below for more tips and ideas.

Uses of Plaster of Paris

The various uses of plaster of Paris include plastering, the base for paintings, sculptures, making chalk, and avoiding fire hazards. It is a beneficial material that is used for both crafts and construction. Let us learn more about this below.


Plaster of Paris can be used for both homes and offices. It provides a fine finish to the walls and the ceilings and also makes them sturdy so that they can last for many years.

Base for Paintings

Plaster of Paris is mostly used in fresco paintings. It is used as a base where the painters can paint. A base that is made from plaster of Paris can last for many years without shrinking.


Plaster of Paris is a strong and durable material that is used in sculpting. Some sculptures and replicas are molded using plaster of Paris so they are not susceptible to decay. Plaster of Paris sculptures and casts are usually used for decorative purposes.

Avoid Fire Hazards

One of the outstanding characteristics of plaster of Paris is that it is a fire-resistant product. Because of this, it is used to coat the walls and ceilings of houses. We have also written this article titled, is plaster of Paris fireproof? Check out the article for an in-depth discussion about the topic.

Make Chalks

Plaster of Paris makes chalks. This is the reason why chalks are hard and do not easily wear out.

Does Plaster of Paris Break?

Regardless of how strong and hard the plaster of Paris is, it is still breakable. Aside from that, it is not suitable for making miniature pieces. Plaster of Paris should be handled with care because they can get damaged when they are dropped to the ground. Aside from that, they can also chip and slough off.

Is Plaster of Paris Easy to Use?

Plaster of Paris is easy to use. It is an excellent material for creating basic sculptures and craft projects. Plaster of Paris can set in just a few minutes. On the other hand, there are some important steps that you need to consider so that you can have a solid and sturdy sculpture or cast. We have also shared this article that discusses if perfect cast is the same as plaster of Paris. You can check out to find out the difference between both materials.

Why Does Plastered Walls Crack when it Dry?

Plastered walls can crack when it dries because of many reasons which include evaporation and suction. Evaporation can happen if the wall is not properly protected from the sun and wind. Because of this, it can crack or even shrink. On the other hand, suction happens if the walls are absorbent and have not been dampened. It can cause shrinkage and cracks. You can also check out this article that discusses if hydrocal expands. We have shared tips and ideas that you can refer to.

How Do You Keep Plaster of Paris from Sticking to the Mold?

To keep plaster of Paris from sticking into the mold, you need to spray the surface of the mold with a mold release agent. You can purchase this at your local arts and craft stores. The mold release agent forms a layer between the mold and the plaster which effectively prevents the plaster from sticking.

How is Plaster of Paris Made?

Plaster of Paris is made by calcining gypsum. This process exposes the gypsum to very high temperatures in order to create calcium sulfate that is then ground into a fine white powder.


In this article, we have discussed if plaster of Paris is hard. We have found out that plaster of Paris is a soft material but can be very hard and strong when made into casts. On the other hand, the plaster of Paris is still fragile and can easily break so you need to handle it with care. Moreover, it is not an ideal material for making very thin casts because it can easily crack. We have also shared tips and ideas on how to make plaster of Paris stronger simply by adding glue into it. Thank you for reading!

Recent Posts