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What Is a Fire Brick?

Dana DeCecco
Dana DeCecco

A fire brick is a molded rectangular block of clay that has been baked and treated to be heat resistant. Refractory applications such as fireplace and furnace lining are some of the uses for fire bricks. Refractory bricks are capable of sustaining intense heat without fusion. Fire brick usually contains aluminum oxide and silicon dioxide. The manufacturing process involves baking the bricks in high temperatures to create a vitrified ceramic product.

Heavy, dense fire brick products are made with fire clay, which contains a suitable content ratio of silica and alumina. These materials last for a very long time and are used in residential, commercial, and industrial furnace and firebox applications. Many industrial uses require specific properties, such as thermal conductivity or porosity, that must adhere to certain specifications. Fire brick properties can be adjusted by adding or adjusting the amount of refractory materials.

The thermal shield used on the space shuttle is a refractory fire brick product.
The thermal shield used on the space shuttle is a refractory fire brick product.

Ordinary dense clay fire bricks absorb and retain heat. Lightweight insulating fire bricks have low thermal conductivity and do not absorb heat well. These products are much softer and incorporate tiny air pockets that exhibit insulating properties. Insulating fire bricks maintain the refractory properties and can withstand very high temperatures; they are widely used in electric and gas fired kilns.

Refractory brick is sometimes used to make fireplaces.
Refractory brick is sometimes used to make fireplaces.

Refractory products are available in the form of bricks and in a wide variety of shapes and sizes. Precast types are manufactured for ferrous and nonferrous metal foundries. The steel, iron, and aluminum industries use refractory materials in the production of metal products. Castable products can be pumped and sprayed for various applications requiring thermal properties. Patching and repair products are made for boilers and furnaces to maintain the longest life possible.

Refractory and fire clay mortar are often used to join fire brick together. Ordinary Portland cement mortar is also used, but common mortar cannot withstand extreme temperatures; as a result, many building codes require the use of refractory mortar. Medium duty and high duty brick and mortar products are available for commercial and industrial applications. Patching and bonding mortars are also available in many forms including caulking tubes.

The many uses of fire brick products make them a versatile and indispensable product. The manufacturing of steel and aluminum require dense refractory products. Kilns are thermally insulated brick chambers used for firing and drying clay and ceramic products. Everything from pizza ovens to fireplaces make use of refractory fire bricks. Even the thermal shield on the space shuttle is a refractory fire brick product.

Discussion Comments


Someone is selling 20 year old Adobe fire brick originally intended for a furnace. They say it can be heated to 3,400 degrees. They also claim it would be good for a pizza oven. Would this be dense or insulating fire brick?


I recently bought firebricks and Portland-Pozzolana Cement to make a pizza oven in my backyard. However, I have not been able to figure out the right composition of the cement/water mixture that I should use to join the firebricks together. When I first tried it, the cement easily came out as if it were 'Plaster of Paris'. The surface of the firebricks is very smooth.

Can anyone please help me out with the cement mixture ratios? Should I add sand to the cement? If yes, how much? And do I also need to keep watering the structure after it has been constructed? For how long and how frequently?

I would really appreciate some help here.


Generally, a "green" brick is defined as a brick which is an amorphous or soft state produced from the clay column coming from the extrude. A "fired" brick on the other hand, is a brick, which once leaving the extrusion device (as a "green" brick), proceeds to a dryer and into a kiln wherein the brick is "firebricks." --Sajal


Does anyone know the best fire bricks for ovens? Is there a certain size or weight we need to buy, or are they all created equally?

We recently decided to purchase one of those old wood burning stoves and are looking to add some fire brick for woods stoves to prevent any accidents. We were told this is one of the best things to purchase.

We were surprised to learn that most fire bricks for wood stoves are usually included in the package, but our purchase just came with the stove. So now we are a bit stuck at figuring out which brick is best to lay in the bottom of our new stove.


@lonelygod - A fire pit is really easy to build, it just takes a bit of hard labor to get it all put together. Plus, a basic knowledge of masonry helps out too.

There are lots of quick tutorials online that can show you how to build a nice pit, and even add a grill for cooking. I really like the designs that add flagstones to the exterior of the pit.

Also, remember when it comes time to choosing fire pit bricks you should talk with the employees at the store you go to. Tell them what you are building and give them your measurements and they can hook you up with everything you'll need.


Can anyone tell me how to build a fire pit with bricks in your backyard?

My family and I have a large property in the countryside and are looking to add some elements to it that will make it possible to have better parties. We have already installed a deck along the back of the house which features one of the really nice fireplace designs we found online.

We are hoping that installing our own fire pit will save us a bit of cash, as we spent quite a lot getting our deck up and usable. We consider the addition a good investment though, as we entertain a lot for our workers.

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    • The thermal shield used on the space shuttle is a refractory fire brick product.
      By: Kim Warden
      The thermal shield used on the space shuttle is a refractory fire brick product.
    • Refractory brick is sometimes used to make fireplaces.
      By: nyul
      Refractory brick is sometimes used to make fireplaces.