Brick
A brick is a block made of kiln-fired material, usually clay or shale, but also may be of mud, etc. Clay bricks are formed in a moulding (the soft mud method), or in commercial manufacture more frequently by extruding clay through a die and then wire-cutting them to the proper size (the stiff mud process). Brick made from clay that is hardly more than dampened must be formed in molds with a great deal of pressure, usually applied by a hydraulic press. These bricks are known as hydraulic-pressed bricks, and have a dense surface which makes them suitable for facing work. The shaped clay is then dried and fired to achieve the final, desired strength. Usually this is done in a continuously fired kiln, in which the bricks move slowly through the kiln on conveyors, to achieve consistent physical characteristics for all bricks. When other than the ordinary structural clay brick is meant, a descriptive term such as fire-brick, sand-lime brick, etc., is employed.
Construction and types
Bricks are used for structural purposes in buildings, for paving, and for lining furnaces. The latter type of brick is known as refractory or fire-brick. Hard-burned brick should be used for face work exposed to the weather, and soft brick for filling, foundations, and the like. The standard brick measures approximately 2.25 x 4 x 8 inches, and has a crushing strength of between 1000 and 3000 lb/in² (7 to 21 million pascals) depending on quality. A highly impervious and ornamental surface may be laid on brick either by salt glazing, in which salt is added during the burning process, or by the use of a "slip," which is a glaze material into which the bricks are dipped. Subsequent reheating in the kiln fuzes the slip into a glazed surface integral with the brick base.
Fire-brick
A refractory brick is built primarily to withstand temperature. This does not usually accompany resistance to heat flow; in fact, most refractory bricks usually have the highest thermal conductivities. This is logical, as thermally-related fractures are caused by tensions within the mass of the material. In turn, these fractures are caused by different degrees of dilation within the mass; these varying degrees are caused by different degrees of heat being absorbed by thermally non-conductive materials. Using a thermally conductive material negates the whole causality chain presented here by allowing the material to absorb heat uniformly, thus dilating uniformly and avoiding the internal tensions which lead to fracture. It is important for refractory brick to have a high resistance to erosion by ash-laden gases and to the fluxing action of molten slag; it should not spall badly under rapid temperature change, and its structural strength should hold up well under rapid temperature changes. Fire-brick is baked in the kiln until it is partly vitrified, and for special purposes may also be glazed. Fire-bricks usually contain 30-40% aluminium oxide and 50% silicon dioxide. For bricks of extreme refractory character, the aluminium oxide content can be as high as 50-80% (with correspondingly less silica), and silicon carbide may also be present. The standard size of fire-brick is 9 x 4.5 x 2.5 in.
Proportions
Regardless of size, bricks are always manufactured with the depth equal to half the length (assuming that the brick is laid horizontally). This allows for several convenient layouts which must necessarily interweave the bricks in any structure, often both at the corners and within the wall depth in order to ensure the greatest possible durability of the structure.
See also
In role-playing games, a brick is a character whose main useful skill is being able to take a great deal of damage (usually physical damage) and act as a shield for weaker allies. These characters are also usually quite strong, but slow.
