FIRE BRICK and REFRACTORY BRICK

What you need to know before purchasing Refractory Brick

by Jim Wunch

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Refractory Materials

Refractory materials (materials that can withstand high temperatures) are used in the construction and maintenance of ceramic studio kilns. Fire brick, ceramic fiber and castable refractories are the three forms of refractories used in kilns, but fire brick is the most significant.

A Brick with Many Faces

Fire brick is a generic term that encompasses any brick that can withstand repeated heating and cooling at various temperature ranges. Additionally, fire bricks must be able to withstand different atmospheres, provide various structural or insulating qualities, and due to the difficulty in cutting them, must be available in a variety of shapes to add flexibility to kiln design and construction.

Hard and Soft

There are two types of firebrick: hard brick and soft brick. Hard bricks are very dense and durable and used for their structural qualities. They can be found most often as the main building component of large kilns, chimneys, fireboxes and burner ports—anywhere around direct flame. Soft bricks are lightweight and made from a refractory clay body containing combustible materials. When fired, the materials burn out leaving a sponge like matrix of air pockets, which serve to provide insulating qualities to the brick. Also known as insulating firebricks (IFBs), these bricks absorb about half the energy as hard bricks during a firing. Soft brick ranges from 2000°F to 3300°F and are used as the brick of choice for constructing electric kilns or as insulating liners in reduction kilns.

Hard and Soft

There are two types of firebrick: hard brick and soft brick. Hard bricks are very dense and durable and used for their structural qualities. They can be found most often as the main building component of large kilns, chimneys, fireboxes and burner ports—anywhere around direct flame. Soft bricks are lightweight and made from a refractory clay body containing combustible materials. When fired, the materials burn out leaving a sponge like matrix of air pockets, which serve to provide insulating qualities to the brick. Also known as insulating firebricks (IFBs), these bricks absorb about half the energy as hard bricks during a firing. Soft brick ranges from 2000°F to 3300°F and are used as the brick of choice for constructing electric kilns or as insulating liners in reduction kilns.

Grades Are Important

The main ingredient in fire bricks is fireclay, which contains mostly alumina and silica, elements capable of withstanding high temperatures. Hard bricks are available in several grades, depending on their composition and properties, which determine the most efficient use of them in construction. High alumina compositions start at 50% alumina and increase in alumina content to 98% for the highest purity and most expensive. It’s extremely rare that a potter would require an alumina content exceeding 70%.

Low-duty: Typically rated to 1750°F maximum service temperature. Primarily used for fireplace chimneys and contains 24–26% alumina.

Medium duty: Temperature rating to 2700°F maximum service temperature. Uses include backup linings, lower-temperature ceramic kilns and chimneys, and contains 34–38% alumina.

High Duty (first-quality firebrick): Temperature rating to 2850°F maximum in purely heat service. Certain atmospheres can reduce this temperature rating by several hundred degrees and contains 36–40% alumina. Uses include boilers, ceramic kilns, chimneys and back-up linings.

Super Duty: Temperature rating to 2900°F in pure heat service. Certain atmospheres can reduce this temperature rating by several hundred degrees. Same uses as high duty where higher temperatures are involved. Contains 40–44% alumina.

High-Fired Super Duty: Temperature rating between 3000°F–3150°F. A higher burned version of super duty firebrick designed to lower the porosity, increase physical strength and improve resistance to alkali attack and carbon monoxide disintegration. Contains 40–44% alumina.

Shapes
Most bricks are pressed or extruded. Common shapes are straights, arches, wedges, keys, rotary kiln blocks (RKBs) and square-edge tiles. Larger pieces are typically produced by air hammering the brick mix into wooden or steel molds sized for the desired shape dimensions.

The standard refractory brick size is 9×4½×2½ inches, also known as one brick equivalent (beq). This size is the most common used in pottery kiln construction. However, an equally popular standard size used in industrial furnace construction is the 9×4½×3-inch series. The 3-inch series brick reduces the number of joints in the kiln.

Straights - The standard straight is 9×4½×2½ inches or 9×4½×3 inches and available in larger sizes up to 18 inches long, 9 inches wide, and 4½ inches thick.

Square edge tile - This term refers to “big” straights, which comprise 12×12 inches up to 24×12 inches with thickness ranging from 1½ to 3 inches.

Soaps - A term used to describe a half brick in width such as 9×2¼×2½ inches or 9×2¼×3 inches.

Splits - A term used to describe the thickness of a brick thinner than 2½ inches, i.e., splits come in 1, 1¼, 1½, and 2-inch thicknesses.

Arch - This shape tapers in thickness along the width over its entire length and is used to make sprung or circular barrel arched roofs either 4½ inches or 6 inches in thickness.

Wedge - This shape tapers in thickness along the entire length of the brick and is used to make sprung or circular barrel arches 9, 12 or 13 inches in thickness.

Skew - A shape having a certain taper on one side or end to enable a sprung arch to be built. Four major types are available in both side and end skews that relate to the rise of the arch.

Recommendations
Here are some recommendations that will greatly assist you on your firebrick purchase.

• The vast majority of pottery kilns are constructed of high duty or super duty brick.

• Use extreme care when considering used refractories for building kilns. In most cases, you won’t know the conditions under which they were exposed. If they’ve been removed from a furnace, it’s usually because the lining failed. Properties of refractories deteriorate with exposure to extreme heat, chemical vapors, mechanical stress and thermal cycling.

• While insulating firebricks can be easily cut with any kind of saw, hard bricks require special equipment, like a tile cutting saw, to cut. Design your kiln to take full advantage of available shapes, and when possible to minimize the amount of hard bricks you must cut.

Jim Wunch is the owner of Larkin Refractory Solutions located in Lithonia, Georgia. He has more than thirty years of professional experience with refractory manufacturers and installers worldwide.


Fire Brick Home Depot 

Since its inception in 1978, Home Depot has rapidly gained recognition as the largest home improvement superstore in America. With over 2300 stores in operation, it is likely that there is a Home Depot within a 15-mile radius of almost every medium and large city. So… does this mean that you can find fire bricks at any Home Depot location without needing to inquire about availability beforehand? Well, not exactly. Fire brick may not be available at every Home Depot location, and it is highly advisable to call your local Home Depot and inquire about their fire brick inventory before driving over to your local store. Moreover, upon arrival, you might discover that the new hire wearing an orange vest that you spoke with on the phone mistakenly referred to clay brick instead of fire brick… which not the same thing (see Clay Fire Brick vs. Silica Fire Brick).


When contacting your local Home Depot regarding fire bricks, it is advisable to specifically reach out to a representative at their PRO-DESK. The employees behind the Pro-Desk at Home Depot are usually industry experts that have previously worked as contractors, masons and/or construction journeymen and they retain vast amounts of knowledge about construction materials. Therefore, it is in your best interest to consult with a Pro-Desk agent when seeking information about fire bricks (as well as other materials). The Pro-Desk agents will likely be familiar with fire brick and can provide you with a definitive inventory inquiry… or recommend local sources for purchasing fire bricks.


During your Home Depot fire brick phone conversation, take the opportunity to inquire about the availability of fire bricks at other Home Depot locations nearby. It's important to note that if your local Home Depot store doesn't have any fire bricks in stock, there is still a possibility that another nearby Home Depot might have a pallet of fire brick. In such cases, there is a good possibility for Home Depot stores to transfer their inventory of fire bricks between stores.


Another benefit of shopping at Home Depot for Fire Brick is that many of their locations carry Sakrete High Heat Mortar. If you're in the process of building a Mattone Barile or Mattone Barile GRANDE pizza oven kit, this factory blend of high-temperature, non-water soluble mortar is exactly what you'll need to construct your fire brick pizza oven. And if you do decide to buy pre-mixed fire brick mortar from Home Depot, there's no need for you to create your own high-temp mortar using fire clay, hydrated lime, portland cement, and fine-grain sand.


Home Depot Fire Brick

The Home Depot Fire Brick online inventory tracker is known for its reliability; however, we highly recommend that you verify the availability of items with a quick phone call before making a trip. Additionally, it's advisable to check nearby Home Depots for their fire brick inventory. If other branches have fire bricks in stock, reaching out to an expert behind the Home Depot Pro-Desk and requesting a transfer of fire bricks from the stocking Home Depot location to your preferred Home Depot would be beneficial.