Fire bricks are special types of brick meant to be used in places where extreme temperatures are expected. Furnaces, fireplaces, outdoor pizza ovens are some of the places where we need to maintain the heat inside, however, it is impossible to work close to them if these temperatures are not stopped from escaping outside. Hence, bricks made out of a special ceramic material are used to line the walls, floors and ceilings of such areas. This ceramic also known as refractory ceramic is made specially to withstand extremely high temperatures and also helps in keeping the heat trapped inside the chamber. This quality is attributed to their low thermal conductivity.
Firebricks are made of a special mixture consisting high percentage of Aluminium Oxide and Silicon Dioxide and also some amount of calcium, sodium and potassium oxides. This clay is baked in the kiln, to form the fire bricks. The size of a standard fire brick is 9 x 4.5 x 3 inches or 230 x 114 x 64 mm. Although it may differ depending on the usage.
The various applications require different types of fire bricks for example, the refractory bricks used in an industrial furnace would not be suitable for a small pizza oven or a fireplace and vice versa. The types of fire bricks vary in terms of density, variation of chemical composition etc. One can find fire bricks tailored toward a very specific application, although broadly classified, following are the different types-
Clay Brick – The most common type of firebrick is a clay brick. Clay is baked at high temperature to make the brick smooth and hard. These bricks can survive fairly high temperatures but will eventually crack and will need to be replaced. Because of this its not wise to use them inside the ovens. As they come in various shapes and sizes, they are more suitable for decorative purposes. Outer surfaces of ovens can be decorated with fire clay bricks.
Medium Duty – Medium duty bricks are best to use in small to medium size ovens generally built in homes and restaurants. Suitable for both indoor and outdoor use, these bricks warm very quickly and also cool down pretty fast (A phenomenon known as thermal cycling). Medium duty firebricks can provide insulation from temperatures as high as 1400 degrees Centigrade. Composed of about 30% alumina and 50% silica, these bricks don’t crack very easily and are fairly durable. Using medium duty bricks instead of the clay bricks will increase the shelf life of your oven.
Keep in mind that the edges of the bricks are straight and there is no gap between adjacent bricks for efficient functioning of the oven.
Heavy Duty – Industrial furnaces and kilns require that the bricks withstand extremely high temperatures and are much more rugged. High or heavy duty firebricks are specially manufactured for this purpose and can consist of up to 50% alumina and hence they can stand up to 1500 degree centigrade. Since high duty firebricks can hold very high temperatures, they are not suitable for home ovens or other such applications.
Insulation fire brick - The insulation bricks are firebricks generally used in fireplaces as they themselves do not hold any heat, and are designed to stop heat from exiting the chamber.