What is Hydrocal?

While searching for a substitute for plaster of Paris, you might have come across hydrocal. What is it and can it be used as an ordinary plaster? 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.

What is hydrocal? Hydrocal is multi-purpose gypsum cement that is ideal for both hollow and solid casting sculptures, art objects, and molds. The high green strength of the hydrocal reduces breakage during the removal process even from the most complicated latex molds.

What is hydrocal made of? Is there any difference between hydrocal and plaster of Paris? What are the main features of hydrocal? These are some of the questions that we will talk about in this article. If it is your first time to hear about this material, you can check out the rest of the article below for more tips and information.

What to Know About Hydrocal?

Hydrocal is a gypsum product that is commonly used for slip latex mold sand case molds. It provides a slightly better heat resistance as compared to pottery plaster with higher dry and wet strengths. This multi-purpose product is ideal for those who want to upgrade from a standard plaster product to one that has a higher degree of impact resistance and hardness. Hydrocal is also compatible with many color pigments.

What are the Main Features of Hydrocal?

Hydrocal provides twice the compressive strength of plaster and is ideal for thin and delicate sections where high green strength is needed.

  • Provides long workability as setting expansion is twice that of molding plaster and pottery plaster
  • Ideal for both hollow and solid casting lamp bases, moldings, general castings, and figurines
  • Sets 25 to 35 minutes after mixing
  • Provides a great value to performance ratio
  • Requires 45 parts water by weight per 100 parts plaster
  • Has a stark white color which makes it ideal for accepting colorants

What is Hydrocal Made of?

Hydrocal is mainly composed of plaster of Paris and a small amount of Portland cement. It has a similar formula as hydrostone, duracal, and ultracal. They are all used for casting sculptures and making 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 the topic.

How do You Use Hydrocal?

Like any other gypsum product, hydrocal will vary slightly from batch to batch as far as the amount of water required for mixing. The mixed consistency will vary depending on its use. Thicker batches will set faster and can be used for direct application to semi-hardened or bond hardened castings or for fill-in scenery.

How to Mix Hydrocal

Below is a step-by-step instruction on how to mix hydrocal

Step 1: Use portable water between 70 to 100 degrees Fahrenheit. Take note that variations in slurry temperature result in variations in setting time, it is vital to keep both hydrocal and water at a stable temperature before use.

Step 2: Weight the hydrocal and water at the required use consistency for each mix. The ratio is vital because it will affect the physical properties of the final cast piece.

Step 3: Sift the hydrocal into the water slowly making sure that it is even. Let it soak for one to two minutes. Make sure that the hydrocal is fully dispersed in the water before mixing.

Step 4: Mix the hydrocal. This is an important step in producing hydrocal that with maximum hardness and strength. Make sure that you thoroughly mix the slurry to get the best results.

Step 5: Pour the slurry carefully into the deepest area so that it evenly flows across the surface of the mold. This will prevent air bubbles and will also create a uniform and smooth surface.

Step 6: Allow the hydrocal to dry. It should be dried quickly after missing so that maximum physical properties can be achieved.

What is Lightweight Hydrocal?

Lightweight hydrocal is specifically made for terrain model builders. It is half the weight of hydrocal plaster and goes twice as far. Lightweight hydrocal is a tough, quick-setting product. You can use this product to cast rocks or make your castings. You can also check out this article that we have shared that discusses the difference between hydrocal and ultracal. We have shared an in-depth discussion about the topic.

How to Mix Lightweight Hydrocal

Step 1: Pour 1 ¼ cups of lightweight hydrocal slowly into ½ cup of water.

Step 2: Let it soak for about two minutes then stir for one minute.

Step 3: Mix thoroughly.

What is Hydrocal Used For?

Hydrocal is stronger than plaster but is as easy to use. It is the perfect choice for making a solid and hollow casting of figurines, general sculptures, and commercial casts. Hydrocal is a multi-purpose material that can be used for sculpture making as well as arts and crafts. Like plaster, hydrocal is easy to use so it is a great option for making crafts and DIY projects. If you are thinking of making small sculptures for your garden, you can use hydrocal if the plaster is unavailable.

How to Work with Hydrocal for Castings

Step 1: Prepare the Molds

Wash the molds on the sink. Once they are clean, prepare them for casting by wetting them with a 50/50 mix of laundry detergent. Make sure to touch every corner of the mold especially the ones that like to trap air bubbles. Dilute the detergent by spraying the mold with straight tap water. Shake off the excess water and lay the molds on the table to the floor.

Step 2: Mix the Hydrocal

Follow the instructions on the label on how to mix the hydrocal. Work with the mixture until you have a smooth and consistent mix. You need to achieve a nice thick soupy consistency. Tap the bottom of the mold to help remove bubbles on the mixture.

Step 3: Pour the Hydrocal into the Molds

To avoid splashing the mixture, use the stirring stick as a guide when pouring the hydrocal into the molds. Shake the bubbles out and level of the castings. Scrape the excess plaster off with s metal straight edge to achieve a nice smooth back on the castings. The castings can set in about 15 to 20 minutes.

Video – Lifecasting Tutorial: Mixing Hydrocal Plaster

Brick In The Yard Mold Supply shared the video below on YouTube. It demonstrates mixing tips for white hydrocal. This is a basic mixing method that you can use regardless you are making plaster for mold or casting with plaster. You can check out the video below for the step-by-step tutorial.

What is the Difference between Hydrocal and Plaster of Paris?

People who have used both materials have varied inputs when it comes to the difference between hydrocal and plaster of Paris. Some say the difference is in the component while others say that there is no difference at all. For most, the main difference between hydrocal and plaster of Paris is that hydrocal is much stronger and takes more detail. Moreover, hydrocal does not slough off as compared to plaster of Paris.

When plaster of Paris sloughs off, it results in dust and chips continously. To remedy this, you can seal the plaster of Paris. However, most sealers cause the plaster to have a sheen, do not take stains, and do not make the finished scenery any stronger or damage resistant. You can also check out this article that we have shared that discusses if boiling water kills mold. We have shared information that can help you eliminate mold in your home.

Hydrocal Vs. Hydrostone

Hydrostone and hydrocal are both gypsum products. The difference is that hydrostone is considerably harder and lacks the period of plasticity in the setting curve which enables the plaster to be worked directly. It is considered the strongest and hardest gypsum cement available.

Hydrostone are commonly used in tooling and high-quality art object application. It is also an extremely wear-resistant material. When working with hydrostone, immediately do surface clean-up on demolding as it will continue to harden for several hours thereafter.

How to Make Homemade Plaster

You can use white glue, white flour, or Paris powder as a substitute for plaster. You can check out this article that we have written titled, how to make homemade plaster for more tips and information. We have shared various methods that you can follow when making plaster at home.

How Long Does Hydrocal Take to Cure?

It can take up to 23 to 35 minutes or more for a hydrocal to cure and have a thick surface. If you want it to be thoroughly cured before de-molding, you need to wait until it feels warmish and dry.

Is Hydrocal Waterproof?

Hydrocal is waterproof. Aside from that, it is also weatherproof and scratch-resistant.

How to Make Plaster of Paris Stronger

Mixing glue into the plaster of Paris mixture will make it more durable and strong. Find out how to do this by reading the article that we have shared titled, how to make plaster of Paris stronger. We have shared the step-by-step methods on how to mix glue with the plaster.

Where to Buy Hydrocal?

You can check your local hardware supply for hydrocal. Some pottery, ceramic, and art supply stores are also selling hydrocal. For easy and convenient shopping, you can look at online stores for a wide array of products that you can choose from.


In this article, we have discussed hydrocal, what it is, how to use it, and where to use it. We have also learned the difference between a hydrocal and plaster of Paris. If you are looking for a good substitute for plaster of Paris, you can consider using hydrocal. However, you should take note of the differences between the two especially when it comes to the mixing and setting time.

We hope that this article has helped you learn more about hydrocal and help you get ready for your next sculpting or molding project. Thank you for reading!

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