Fire bricks

Supplying fire bricks

A fire brick, firebrick, or refractory brick is a block of refractory ceramic material used in lining furnaces, kilns, fireboxes, and fireplaces. A refractory brick is built primarily to withstand high temperature, but will also usually have a low thermal conductivity for greater energy efficiency. Usually dense firebricks are used in applications with extreme mechanical, chemical, or thermal stresses, such as the inside of a wood-fired kiln or a furnace, which is subject to abrasion from wood, fluxing from ash or slag, and high temperatures. In other, less harsh situations, such as a natural gas fired kiln, more porous bricks are a better choice. They are weaker, but they are much lighter, easier to form, and insulate far better than dense bricks. In any case, firebricks should not spall under rapid temperature change, and their strength should hold up well during rapid temperature changes.



Do not confuse lightweight insulating fire bricks with heavy dense firebricks. Insulating bricks are refractory too and of course withstand very high temperatures range BUT for purpose they have very low thermal conductivity and don’t absorb the heat well at all. Those are intentions for heat insulation. For instance if you used them for building of the hot face in a wood fired oven (for cooking) the oven wouldn’t cook, because it wouldn’t store and hold almost any heat.  



You can however use these insulating fire bricks on the outer side (of the heavy firebrick walls, vault or under the floor bricks and slab) to prevent the soaked in heat in the chamber’s body mass from escaping and achieving superb results. Meaning well insulated oven which will hold the absorbed heat in its mass, where it should be to cook for long time


How to use light weight fire bricks insulation

Use of light weight fire brick insulation is broad, mainly in industrial and hobby kilns heated up with either electric spiral elements or gas burners, furnaces, both for hot face lining or outer back-up heat insulation.


Insulating fire bricks are soft and light in weight. They can be easily cut by handheld hack saw or any other hand tool like chisel or even drill bit. Color of insulating bricks varies but usually they come in shades from light brown to white, see pictures. In refractory air is the best insulation and this is why insulating firebricks have excellent insulating properties. Their body is made of tiny air spaces similar to honeycomb effect.


Brick Primer: Choosing the Right Brick Oven Bricks

Deciding what type of brick you will use is one of the first choices you will have to make when starting to build a Pompeii Oven. You will use brick in the cooking floor, the oven dome and perhaps for your decorative vent arch, oven landing and other decorative trim.

This page explains the different types of bricks and what the trade-offs are between them. It should help you decide what types of brick you are going to use, and it can help you find the right brick at your local masonry supply store. It might be useful to take this page with you when you go shopping.


FIrebrick Comparison

Alumina (%)
Density (lb./cu/ft.)
Service Temperature (F)




Here are some basic brick types: 


Medium duty firebrick. This is the brick that we recommend for both the cooking floor and dome of the Pompeii oven. medium duty firebricks are comprised of roughly 35% alumina and 50% silica, heat up quickly, easily withstand the 900F heat your oven will reach, and are designed for the rapid heat-up and cool down (thermal cycling) that your oven will experience. Firebrick will also reach the heat required for pizza more quickly than clay brick, as they are more efficient at conducting heat.

Further, because firebrick is designed to withstand thermal cycling, your oven will last longer, though for most home ovens this is not an important issue, and your oven will probably outlast you whichever brick you choose.

When choosing your firebrick, look for a brick with straight edges for your cooking floor. It is important that the bricks in the floor fit snuggly against each other, and a curved edge will result in a gap between the bricks and in your cooking floor.

A typical firebrick measures 9"x4.5"x2.5", weighs about 8 pounds and is yellow. The price of a good quality firebrick should be around $1.20.


Red clay brick. This is the traditional red clay brick that you find at Home Depot and at masonry supply stores. Clay bricks are made from clay, and fired in a kiln. They are typically made from local clay, as shipping is too expensive, and fired to between 2000F - 3000F (high enough to fuse the minerals). You can use clay brick in the oven dome, but we would not recommend using them in the oven floor. There are trade-offs to consider.

There are two shortcoming to using a clay brick in your oven dome. First, thermal cycling will cause clay brick to spall, where little pieces of the brick flake off, and could cause individual clay bricks to crack. It has happened to us. Second, clay brick is not as good a conductor as fire brick and as a result will take longer to heat up.

Still, you can find clay bricks for about $.50 at Home Depot, which make them the most cost-effective option.

Our view is that unless cost is a prohibiting factor, we would recommend firebrick. For example, a 42" oven some has roughly 180 bricks in the dome, so the difference in brick cost should be around $100. In the context of the overall cost of the oven, and large amount of human capital you will be investing in your oven, we think the extra cost of worth it.

If your choice is to build your oven with clay brick or not at all, we would strongly recommend building your oven with clay brick.

Red clay bricks are typically used for building the decorative arch and optional sides around the oven vent and vent landing, and can be used for any decorative feature.

There are three types of brick that you should avoid.


Concrete brick. These are the concrete bricks you see at Home Depot for about $.12. They are made from standard Portland cement-based concrete and are air dried, not kiln fired. They will not withstand the heat inside your oven.


High duty fire brick. These brick have very high alumina content, get very hot (1500F and up) and are designed for continual high-heat applications, such as furnaces. They are expensive, and will get too hot for some of your oven uses, such as baking bread and roasting. In general, pizza wants heat between 750F and 900F, while bread and roasts cooks best between 500F and 600F. (Note that brick ovens are able to cook at higher temperatures without burning because of the moist heat inside the oven and shorter cooking times.)


Insulating fire brick. These light-weight refractory bricks are designed to stop heat, and as such have low conduction and low heating holding capacity. They are often used to insulate industrial equipment. A typical insulating fire brick weighs about 2 lbs, compared with an 8 lb standard duty firebrick.