What is Hydrocal Made Of?

Are you wondering what hydrocal is made of? Hydrocal is one of the materials used in crafts, molds, and casts. You can find various kinds of hydrocal on the market and you can even purchase online. In this article, we will discuss what hydrocal is made of and what makes it different from other gypsum products.

What is Hydrocal made of? Hydrocal is a US Gypsum product that has a main component of plaster of Paris mixed with a small amount of Portland cement. It is used for casting sculptures, art objects, and for making molds as well.

How to mix hydrocal? Does hydrocal expand? How to use hydrocal? Is water purity important when mixing hydrocal? These are some of the questions that we will discuss. Check out the rest of the article below for more tips and ideas about the product.

Does Hydrocal Expand?

Hydrocal expands. It has a setting expansive that is twice as compared to other plasters. Aside from that, it also offers long workability and has a compressive strength than plaster. Hydrocal is ideal if you are working on thin and delicate sections where greater strength is needed. Moreover, hydrocal is suitable for hollow and solid castings. It has an original stark white color, but you can add colorants of your choice to make it look more vibrant. Hydrocal is also durable which lessens breakage when it is removed from latex molds.

How to Mix Hydrocal

You can mix hydrocal by hand or with the use of a mechanical mixer. You need to follow specific standards and procedures to achieve the full benefits that the product can provide. To successfully mix hydrocal, all the plaster particles should be thoroughly dissolved in the water to create a uniform and even slurry. Aside from that, you also need to make sure that the mixing time, batch size, temperature, and water purity are controlled.


The first thing that you need to do before mixing the hydrocal is to sift it. Sift the hydrocal powder slowly and evenly into the water. Avoid pouring a large amount of hydrocal into the water at once. Let it soak for about two to four minutes and mix it according to the instructions found on the packaging.

Mixing by Hand

If you want to hand mix hydrocal, make sure that you work on small batches preferably up to five pounds. On the other hand, you need to take note that the energy that is put in the mixing process affects the physical properties of the hydrocal. Because of this, hand mixing hydrocal does not often result in a cast with the best properties.

Mixing Using Mechanical Mixer

When using a mechanical mixer to mix hydrocal, it should be done at a speed of 1750 rpm using a direct-drive propeller mixer that is placed in a stand. The mixing shaft should also be angled at 15 degrees vertically. There should be one to two inches of space between the bottom of the container and the propeller. Moreover, you need to be careful in operating the machine so that you can avoid forming a vortex while mixing.

Is Water Purity Important When Mixing Hydrocal?

Water purity is important when mixing hydrocal. When mixing plaster, the water that is used should be as pure and clear as possible. Using contaminated water that is composed of high organic impurities, will take a long time for the plaster to set. Aside from that, the soluble salts that can be present in the water can contaminate the surface of the mold while it is drying. As a result, it can form hard spots on the surfaces of the molds and can also affect both mold and cast. Moreover, other chemicals that are present in the water can react with the gypsum and create soluble salts. Hence, it is vital that you use pure and clear water when mixing hydrocal.

What is Hydrocal in Dentistry?

In dentistry, hydrocal can be made into pastes and dental fillings. In the form of a mix of calcium salts, hydrocal can be used for dental treatment to create materials for temporary cavities filling, temporary root canal filling, and many more. 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.

Where to Use Hydrocal

Hydrocal is often used for making lifecasts from molds. It is a strong material but can still retain some properties that are specific to plaster. Hydrocal can be sanded to make it smoother and more refined using steel tools. It is an ideal material for making mother molds as well as support shells. You can also check out this article that discusses what hydrocal is. We have shared an in-depth discussion about the topic.

✅ Video – Moldmaking Tutorial: 2 Piece Hydrocal Plaster Mold for Silicone Casting

Brick In The Yard Mold Supply shared the video below on YouTube. It shows how to make a 2 piece hydrocal plaster mold for silicone casting. In the video, the hydrocal mold process is discussed. It is a simple and excellent way to create mold. Watch the video below for more tips and ideas.

Hydrocal Mixing Ratio

According to manufacturers, the recommended mixing ratio for hydrocal is 45 parts water to 100 parts hydrocal powder by weight. Using this ratio, it will take about 25 to 35 minutes for the slurry to set when it is manually mixed. When hydrocal is mixed with water, it becomes hard and also very hot. Make sure that you follow the manufacturer’s instructions when you are mixing hydrocal especially if it is your first time using this product.

Take note that dust from hydrocal can cause skin, nose, eye, or throat irritation. Wear protective gear such as face masks, goggles, and gloves when working with hydrocal. Moreover, do not mix hydrocal using your bare hands. Use a paint paddle or jiffy mixer to avoid contact with your skin. You can also check out this article titled, what the difference is between hydrocal and ultracal. Check out the article for more tips and ideas.

Tips for Handling Hydrocal

  • Handle hydrocal carefully and keep it covered to avoid spilling.
  • When working with hydrocal, wear a NIOSH-approved respirator to prevent inhaling the dust.
  • Wear protective gloves to avoid getting in contact with your skin. It can cause skin irritation.
  • Maintain a clean and dust-free workspace.
  • Do not mix work clothes with other clothing when doing the laundry.
  • Avoid eating or smoking while working to prevent accidents.
  • Clean the workspace using a wet mop or a vacuum cleaner.

How to Use Hydrocal

Using hydrocal properly is important to make sure that the project that you are working on is of the best quality. Before using the product, take the time to read the information included in the product datasheets as well as in the safety datasheets. Contact the manufacturer if you have questions regarding the product, especially if you want to use it for a particular application and are not sure if it is suitable or not.

Prepare Tools and Equipment

The first thing that you need to do is to prepare the tools and equipment. You can hand mix hydrocal using a plastic-coated straight mixing paddle. Make sure to use tools and containers that are plastic. When using a brush, it should be the bristle type and are disposable.


Mixing is a very important step when working with hydrocal. Hence, you need to use proper working equipment. Moreover, check the hydrocal powder before using it. If it is lumpy, do not use it. The lumps can mean that the hydrocal has been exposed to moisture. Add hydrocal to water and mix thoroughly until you have the desired consistency.


Clean your workspace after every use. Take note that hydrocal slurry can be set underwater so avoid draining leftover hydrocal into the sink. This can cause the sink and pipes to clog. Clean the hydrocal before it hardens. Otherwise, you will have a hard time scraping and removing it.

What is the Difference between Hydrocal and Ultracal?

The difference between hydrocal and ultracal is that ultracal is harder and denser. Moreover, ultracal is advertised by the USG as a tool for making plaster. On the other hand, hydrocal is a casting plaster that has the ability to hold detail well.

What is the Difference between Hydrocal and Plaster of Paris?

The main difference between hydrocal and plaster of Paris is that hydrocal is stronger and can be able to take more detail. You can also check out this article that discusses the difference between hydrocal and plaster of Paris. Check out the article for more tips and ideas about the topic.

Can You Sand Hydrocal?

You can sand hydrocal using steel tools. Hydrocal is ideal for making mother molds. They can also be used for casting lifecast faces from molds. While hydrocal is a strong material, it can retain some of its working properties that are specific to plaster. You can also check out this article titled, what is hydrocal? We have discussed more about hydrocal, its applications, and how to use it.


You have reached the end of this article that discusses what hydrocal is made of. We have also discussed its uses, how to use it, and tips on how to handle hydrocal. We hope that this article has helped you learn more about hydrocal and how it can be used for various applications. Thank you for reading!

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