What Is Grog in Ceramics?

Many people have asked the question of what is Grog in ceramics in the past. Grog is a term used to describe the process of adding material to clay bodies or glazes to reduce shrinkage during firing, improve durability, and add texture.

The most common form of Grog is ground-up fired clay, called “grog” because it resembles gravel. Other materials used as Grog include glass, sand, and even rice hulls.

When calcined or fired, clay becomes harder and denser. Therefore, when adding Grog to a clay body or glaze, one adds already-fired clay.

The Grog will help reduce shrinkage that can occur during the firing process (especially with larger pieces) and also help to make the piece more durable. Adding a Grog to a glaze will also add texture.

This guide will cover some of the basics of Grog and how to use it in your ceramics.

What Is Grog?

Grog, also known as ground-fired clay, is a fine-grained ceramic material. It is made of powdered clay that has been fired in a kiln. The firing process gives the Grog its characteristic porous structure, and this porosity makes it an ideal additive for ceramic bodies and glazes.

It can also be applicable as a filler in plaster and concrete.

Grog is available in a variety of particle sizes. The coarser grades are necessary for fillers, and the finer qualities are useful in bodies and glazes. The choice of particle size will depend on the intended use.

Grog is a crucial component of many ceramic bodies and glazes. It can improve the functional properties of clay bodies and create interesting visual effects in glazes.

Adding Grog to a clay body will increase its shrinkage, and this can be beneficial if trying to achieve a particular shape or size. The porosity of the Grog also makes it ideal for use in raku firing.

Adding Grog to a glaze will create a matte finish. The degree of matte will depend on the amount of Grog used.

You can purchase Grog from ceramic supply stores. It is also possible to make your Grog by grinding up fired clay.

Does Grogged Clay Prevent a Piece from Cracking?

One of the benefits of using Grog is that it can help prevent cracking during firing.

By adding Grog to a clay body, you increase its shrinkage, and this can be beneficial when firing larger pieces as it helps prevent cracking that can occur when the piece shrinks unevenly.

The porosity of Grog also makes it ideal for use in raku firing. Raku is a type of firing where the piece is removed from the kiln while still red-hot. This sudden temperature change can cause the piece to crack, but the Grog helps prevent this from happening.

How to Use Grog in Ceramics

There are a few things to remember when using Grog in ceramics.

  • First, Grog can reduce shrinkage and crack in clay bodies.
  • Second, you can also use Grog to increase the strength of a piece. Third, Grog can help to stabilize glazes and colors.
  • Finally, you can use Grog to create interesting textural effects.

It is essential to use a high-quality grog when using Grog to reduce shrinkage and cracking.

Grog that is too fine can increase shrinkage and crack. Likewise, Grog that is too coarse can also cause problems. The ideal particle size for Grog is between 20 and 40 mesh.

How Does Grogged Clay Affect Glaze?

As you may know, glaze is a glass-like coating applied to the surface of ceramics. You can use a glaze before or after firing.

Firing a glaze onto a piece will cause it to melt and flow, creating a smooth and shiny surface.

In certain circumstances, Grogged bodies for clay may cause the glazes to develop unexpectedly. Because the clay materials react with the chemicals in the glazes, Grogged clay is also better for stretching and shrinking without cracking. It’s also excellent for firing since it’s more flexible and resilient.

Grog may also be useful to give your pottery and ceramic goods a beautiful feel. The temperature at which you fire Grogged clay is also important since it can often fire much quicker.

What is Grog Made from?

what is grog in ceramics
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Grogged clay mainly contains a high concentration of silica and alumina. The silica is from quartz sand, while the alumina comes from clay or recycled fired bodies.

The combination of these materials gives the clay its high degree of plasticity (workability), which is necessary for many ceramic applications. In addition to being an essential component in clay bodies, Grog plays a vital role in glaze formulations.

There are two types of Grog: primary and secondary.

  • Primary Grog comes from the original raw materials used to make the clay body (e.g., quartz sand and clay).
  • Secondary Grog comes from recycled fired products, such as scrap tile or damaged pottery that has been ground up and added back into the clay body.

The particle size of Grog can range from very fine (e.g., 100 mesh) to coarse (e.g., 10 mesh). The coarser the Grog, the more weight it adds to the clay body and the less workable the clay will be.

Coarse Grog is typically applicable in heavy-duty industrial applications, such as brick and tile making. Fine Grog is often useful in porcelain and other delicate ceramics where a high degree of plasticity is required.

The addition of Grog to a clay body has several benefits.

  • First, it increases the body’s strength and durability.
  • Second, it reduces shrinkage and warping during firing.
  • And finally, it adds texture and interest to the surface of the finished piece.

While Grog is essential to many clay bodies and glazes, it’s important to use the right type and particle size for your specific application.

Working with a qualified ceramic engineer or materials specialist can help you select the best Grog for your needs.

Why Add Grog to Clay?

Grog is added to clay to improve its functional properties. Grog increases the clay body’s porosity, making it easier to work with and less likely to crack during shaping and drying.

Grog also absorbs excess water from the clay, making it more pliable and easier to work with.

Clay with a high percentage of Grog can be challenging to work with, however, because it is more brittle and prone to cracking.

Grog also decreases the clay’s fired strength, so it is essential to use a clay body with the right proportion of Grog for the application. Too much Grog can make a clay body unsuitable for some uses, such as making tableware or sculpture.

READ ALSO: How to Make Ceramic Cups at Home?


Grog is a necessary component in many clay bodies and glazes, and it improves the workability of the clay and adds strength and durability. Using Grog’s right type and particle size for your specific application is essential.

Before you begin working with Grog, consulting a qualified ceramic engineer or materials specialist is a good idea. They can help you select the best Grog for your needs and show you how to use it properly.

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