BRICK

a small rectangular block of fired clay used in the construction of foundations, walls, piers, buttresses, and arches of buildings and other structures and in the construction of the ducts, flues, linings, and chimneys of furnaces. By massing bricks in quantity, with mortar joints, greatly varied forms of construction can be erected. Throughout their long history, bricks have varied greatly in size. The term brick is now usually associated with a unit that measures approximately 89 inches (2022 cm) long by 3.754.5 inches (911 cm) wide by 23 inches (57.5 cm) deep. Larger hollow clay units called structural clay tiles are widely used for building in Europe and the United States and can be considered to be a development of the brick. Both these types of brick are made of clay and are fired in a kiln, or oven, to produce strength and hardness. Clays suitable for ordinary bricks are widely distributed. Most of these natural clays are complex mixtures of one or more of the clay minerals (hydrous aluminum silicates) with salts of common elements, such as iron and calcium. The use of bricks may date to more than 6,000 years ago. Primitive bricks were sun-dried, but the brick kiln was invented at an early date; bricks used in Middle Eastern temples and ziggurats built in the 3rd millennium BC were kiln-fired. Sun-dried bricks proved effective only in climates having low humidity and rainfall, and even then they required safeguards against dissolution. From Babylon and other such centres the ancient craft of brickmaking appears to have spread westward to Egypt and the Mediterranean and eastward to India and China. The ancient Romans acquired this knowledge and improved the durability of both brick and mortar, using them in combination with concrete to form the characteristic Roman arches, vaults, and domes. Roman techniques of brickwork were passed on to the Byzantines who, in turn, influenced the Seljuq and Ottoman Turks. Byzantine brick buildings in Italy furnished prototypes for the great Lombard development of brick architecture beginning in the 11th century. Inspired by the Italian example (and perhaps also by the Middle Eastern example through the Crusades), brickwork then began to appear elsewhere and came to dominate the architecture of northern Germany, Denmark, the Low Countries, and parts of England. Western Europe probably made a more thorough use of brick than did any other region of the world. Brick was particularly important in preventing recurrences of the disastrous fires that chronically affected medieval cities. After the Great Fire of 1666, London changed from being a city of wood and became one of brick, solely to gain protection from fire. As increasingly tall buildings were constructed in the second half of the 19th century, their load-bearing exterior walls had to be built of progressively greater thicknesses of brick in order to guarantee the walls' stability. The 16-story Monadnock Building in Chicago (188991), for example, had brick walls 6 feet (2 m) thick at the base, and tapering to a thickness of 12 inches (30 cm) at the top story. For the most part, brick has been replaced by an armature of steel as the load-bearing structure in large modern buildings. Many such buildings are still faced with brick, however, for aesthetic reasons. Modern brick manufacture begins with mining the clay, which is crushed and ground in a mill to a fine grain, then mixed with water to make a stiff paste. The paste is then formed into bricks either by pressing it into molds or by extruding it in a continuous rectangular column, which is then sliced with wires to size. After the bricks are formed, they must be dried in kilns to remove as much free water as possible prior to firing. The green, or partially dried, bricks are then fired in another kiln at 9501,200 C (1,7502,100 F) for about 12 hours. In modern kilns, the bricks are loaded onto cars carrying as many as 3,000 or more bricks. These cars start at the cool end of a long tunnel kiln and move slowly forward through gradually increasing temperatures to the firing zone. After passing through this zone, the bricks pass through decreasing heat zones until cooled. In highly automated brickmaking facilities, the bricks emerging from the kiln are automatically stacked in packages of approximately 500, strapped with metal bands, and are ready for storage or shipment. Sun-dried bricks are known as adobe (q.v.). They are made from heavy clay soil (adobe) that is mixed with a small amount of straw to prevent shrinkage cracks during the drying process. The adobe is shaped into bricks, which are dried in the sun for up to several weeks. Adobe has been widely used in areas of dry climate such as the Middle East, the Mediterranean, southern Spain, and the American Southwest, where the bricks are less likely to be dissolved by rainfall or ground moisture. The three general classes of brick are face brick, which is used where appearance is important; common brick, made of lower-quality clays and used for ordinary construction; and refractory brick, which can resist extremely high temperatures and is used in the construction of furnaces and fireplaces. In the walls of most modern buildings, only the outer layer is made of face brick, which is made to be seen and to withstand weather; the core is made up of common brick, concrete or clay-tile blocks, or poured concrete. Stability in brick walls requires that the separate bricks cling together so that the masonry will withstand loads and stresses and retain its character as one piece. Each layer of bricks in a wall is called a course. Courses laid end-to-end are stretchers, and courses laid side-to-side are headers. The different bonding patterns of brick result from different arrangements of stretchers and headers. Where two or more vertical courses are constructed across a wall thickness, they must be tied by header units (or light-gauge metal ties) to provide structural stability. Among the most common brick-bonding patterns are English bond, which consists of courses of headers alternating with ones of stretchers, and Flemish bond, in which the bricks of each course are alternately header and stretcher, laid so that a header is always over a stretcher. In English bond, one-half of the surface has headers penetrating two brick-widths deep, while in Flemish bond, one-third of the surface is headers. Either bond provides a tremendous interlocking effect and thus contributes greatly to the stability of the wall. Bricks are held together with mortar, an adhesive usually made of cement, lime putty, and sand in various proportions.