Does Hydrocal Expand?

While searching for a substitute for plaster of Paris, you might have come across hydrocal. What is it and does it expand? In this article, we will have an in-depth discussion about hydrocal. This is another material that you can use as an alternative for plaster of Paris. While some of their components are not the same, both are made for the same purposes like casting and molding. Check out the rest of the article below for more information.

Does hydrocal expand? Hydrocal has a setting expansion that is twice as compared to that of a pottery or molding plaster. Moreover, it has a greater compressive strength that is ideal for making thin and delicate sections. It is an ideal material to use for applications that need high green strength.

Is hydrocal a casting material? What is the difference between hydrocal and hydrostone? Is hydrocal stronger than plaster of Paris? How to make castings from hydrocal? These are some of the questions that we will discuss. Check out the rest of the article below for more tips and ideas.

Does hydrocal expand
Image by Hans Braxmeier from Pixabay

Is Hydrocal a Strong Plaster?

Hydrocal is a strong and durable plaster. It can take a lot of detail. Hydrocal does not slough off so you can rest assured that your final casting pieces will not dust or chip continuously. It is ideal for making a long-life scenery base.

How Long Does it Take for Hydrocal to Cure?

It can take about 24 hours or more for hydrocal to cure depending on how thick its surface is. Before demolding, you can find out if it is completely cured once the plaster feels dry and warm to the touch.

What is the Difference between Hydrocal and Hydrostone?

Both are gypsum products, but the difference between them is that hydrostone is harder than hydrocal. Moreover, hydrostone does not have a period of plasticity in the setting curve. Hydrostone is also considered the hardest and strongest gypsum cement.

What is the Difference between Hydrocal and Ultracal?

The difference between hydrocal and ultracal is that ultracal is denser and harder. It is also advertised by USG as a plaster-making tool. On the other hand, hydrocal is a casting plaster that can hold detail well. It is easier to work with and is usually used in post-casting for corrections. You can also check out this article that we have shared that discusses the difference between hydrocal and ultracal. We have shared tips and ideas that you can refer to.

Is Hydrocal a Casting Material?

Hydrocal is a casting material. It can be used for making detailed casts. Hydrocal is fine and fast-setting plaster that is dense and strong. It can be combined with plaster polymer to create castings with fine details. There is a wide array of casting and modeling plaster that is available on the market. Each plaster has different setting times and strengths.

How to Make Casting from Hydrocal

There are a few steps that you need to follow when making castings from hydrocal which include creating the mold, pouring the plaster, and cleaning the cast. Different applications require different setting times, but the process is the same. Let us find out more about how to make castings from hydrocal below.

Step 1 – Make the Master

The first thing that you need to do when making hydrocal castings is to create a master to make your mold. This is also referred to as the plug. A master is an original sculpture that forms the shape of the mold that you will make. Masters can be made using modeling clay, wood clay, or wax clay.

Step 2 – Create the Mold

The next step is to create the mold. To do this, you need to coat the master in a release agent so that the plaster mold will not stick into it. You can choose from a wide array of release agents available on the market.

Step 3 – Choose the Right Mold

Next, you need to choose the right mold. Take note that there are three types of molds that you can choose from depending on the project that you are working on. These are the waste mold, the single-piece mold, and the multi-piece mold. The one that you choose will have to depend on the material that you will use for the master as well as how many casts you need to make. Find out more about these types below.

Waste Mold

This type of mold can only be used once and is ideal to use for a soft master that is made from wet clay or modeling clay. After you have used the mold for casting, you need to chip it away using a chisel.

Single Piece Mold

This type of mold is best for creating simple sculptures that have flat backs and can be used multiple times. You can make a single-piece mold by applying a release agent to the master. Next, you need to build a wall around it and pour the plaster at the top

Multi-Piece Mold

This type of mold is ideal for making complex sculptures. Multi-piece molds have two halves that should be held firmly together when pouring your cast. This mold can be used many times.

Step 4 – Pour the Plaster

The next step is to pour the plaster. Hydrocal is ready to pour once if it has the same consistency as pancake batter. Once you have the right consistency, pour the plaster into the deepest part of your mold. Make sure that you tap the side of the mold to get rid of air bubbles. Allow the cast to dry for about one hour before you remove it from the mold.

Step 5 – Clean the Cast

Once the cast has dried, you need to clean it up to remove any bits of plaster. You need to remove the rough pieces before the cast has fully dried. Remove any bits of plaster using stainless steel modeling tools. It usually takes about three days for the cast to completely dry. Smooth out any rough patches using fine or medium non-clogging sandpaper.

Step 6 – Finishing Touches

Once you have cleaned your casts, you need to do some finishing touches. You can use a natural plaster surface or you can paint it. Take note that plaster is a porous material so it is ideal that you seal the surface using a coat of acrylic paint before you add any colors into it. Adding acrylic paint can provide your final coat of paint with a glossy look to make the colors more vibrant.

✅ Video – How to Cast Hydrostone 101 Use Plaster Cement Casting

HillBrothersVideo shared the video on YouTube. It discusses how to cast hydrostone. In the video, how to mix and use hydrostone to create a casting is shown. Check out the video for tips and ideas that you can refer to.

What is Hydrocal Made Of?

Hydrocal is a US Gypsum product that is made from plaster of Paris and a small amount of Portland cement. Hydrocal, like other plaster such as ultracal, hydrostone, and duracal are used for casting sculptures as well as art objects and molds. We have also shared this article that discusses what hydrocal is made of. Check out the article for more information about this type of plaster.

Can You Carve Hydrocal?

Hydrocal can be carved. While it is a strong rock-hard plaster, it can be carved and cut. Hydrocal that is freshly poured is in a semi-hard state; it can be scribbled and cut. Moreover, hydrocal that is cured can be softened using a few drops of water so that it can be easily carved with a hobby knife.

Can Hydrocal be Used Outdoors?

If hydrocal is sealed, it can be used outdoors. Bear in mind that most plasters are not ideal for outdoor use because it is a porous material. It is not waterproof and can be damaged when constantly exposed to water. On the other hand, you can waterproof hydrocal to make it stronger. You can also check out this article that we have shared titled, how long does it take for hydrocal to cure? We have shared tips and ideas about the topic that you can refer to.

Can Hydrocal be Used in Pottery?

Hydrocal is a material that can also be used in pottery. It has different working properties. Hydrocal is dense, has low absorption, and has a smaller controlled expansion. It is used in making different applications like tooling for slip casting, template turning, permanent models, and figurines.

Is Hydrocal Stronger than Plaster of Paris?

As compared to plaster of Paris, hydrocal is stronger and can also take more detail. Moreover, it is easier to work with and is more durable. The good thing about plaster of Paris is that it does not slough off which makes it ideal for making long-life scenery. For more information about this topic, you can check out this article titled, is hydrocal stronger than plaster of Paris? We have shared an in-depth discussion about the topic.


You have reached the end of this article that discusses if hydrocal expands. We have also discussed its other properties and how to make a casting out of it. Hydrocal is a string and durable material which is used in different applications. We hope that this article has helped you learn more about hydrocal. Thank you for reading!

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