Bricks are among the oldest construction materials known. The raw materials needed to make them are found almost everywhere, and the method of making them is very simple. The Sumerians were using plano-convex bricks, flat on one side and curved on the other, as early as 4000 B.C.. Brickwork at Ur showed traits of sophistication, included corbeled vaulting. At the time bricks were often stamped with the names of their makers.
Brick-making spread to Persia, India, China, Greece, and eventually to most of the world. In some areas, such as Egypt, stone was reserved for official buildings and the homes of the privileged, while sun-dried brick was used in common construction. In other areas, brick was preferred for the officials while wood and other less permanent materials were left to the commoners. Sun-dried brick was adequate as long as there was no danger of destructive rains. Even so, the Egyptians and many other ancient peoples often found it desirable to strengthen their sun-dried bricks by scattering chopped straw around the brick pits and then walking about the pits to mix the straw with the clay, literally "treading the mortar" as references in the Bible suggest.
In wetter climates, bricks required kiln-firing to made them hard enough to fend off moisture. Brick kilns, or ovens, have been used for millennia, and the decision to adopt baked or unbaked bricks was sometimes as much a matter of cultural choice as of technological necessity. By the seventh century B.C., straw was no longer mixed in the clay, but the clay was still "trod" to ensure an even distribution of moisture and proper baking in the kiln.
Most of the natural clay used for bricks are complex mixtures of clay minerals with salts of common elements like iron or calcium mixed in. Bricks are held together with mortar, an adhesive usually made of cement, lime putty, and sand in various proportions. Brick-making in Europe, like many other technical advances, died with the Roman Empire. There was a lengthy period in which only the most basic construction techniques were practiced during the Middle Ages. Not until the 1500s, when King Henry VIII promoted it, was the use of brick revived in England. In 1619, a clay working machine was patented, and after London burned in 1666, brick-making making flourished.
European brick construction was introduced to North America in Virginia in 1611 and in Massachusetts in 1629. However, the adobe cultures of what is now the Southwest United States and Mexico had already been building their cliff dwellings with brick for centuries. (Adobe is the Spanish word for unbaked brick.) Advances in brick-making continued when Apollos Kinsley of Connecticut patented a brick-making machine in 1793. It consisted of a mill with an auger that forced clay into molds. A type of reinforced brick was introduced in the early 1800s, and iron and steel were used to strengthen the clay instead of straw. In 1825, Marc Isambard Brunel used bricks reinforced with wrought-iron bolts in his Thames River Tunnel project.
The revolution in construction that occurred in the late 1800s shifted structural support from building walls to iron or steel frameworks. Brick became a facade material, still of great importance, but no longer the main ingredient in a building's support. Yet, for several decades, brick was nearly the only facade material in use in some cities. Brickyards were as numerous as breweries at the turn of the twentieth century. It was also used to pave city streets and river wharves (cobblestones). In some areas, bricks were being made from granite blocks. Brick was used extensively in residential construction after World War II. Commercially, however, it took a back seat to glass and steel. After some thirty years of futuristic modern architecture based on glass and metal, brick is making a comeback as an attractive embellishment to high-rise buildings and shopping centers. It is also being used once again to pave sidewalks. After several millennia, the principles of brick-making have remained virtually unchanged.
The use of brick has varied, but its role in the construction industry seems assured.
Brick is an artificial stone made by forming clay into rectangular blocks which are hardened, either by burning in a kiln or sometimes, in warm and sunny countries, by sun-drying.
History
In the Near East and India, bricks have been in use for more than five thousand years. The Tigris-Euphrates plain lacks rocks and trees. Sumerian structures were thus built of plano-convex mudbricks, not fixed with mortar or with cement. As plano-convex bricks (being rounded) are somewhat unstable in behaviour, Sumerian bricklayers would lay a row of bricks perpendicular to the rest every few rows. They would fill the gaps with bitumen, straw, marsh reeds, and weeds.
The Ancient Egyptians and the Indus Valley Civilization also used mudbrick extensively, as can be seen in the ruins of Buhen, Mohenjo-daro and Harappa, for example. In the Indus Valley Civilization particularly, all bricks corresponded to sizes in a perfect ratioof 4:2:1, and made use of the decimal system. The ratio for brick dimensions 4:2:1 is even today considered optimal for effective bonding.
The Romans made use of fired bricks, and the Roman legions, which operated mobile kilns, introduced bricks to many parts of the empire. Roman bricks are often stamped with the mark of the legion that supervised its production. The use of bricks in Southern and Western Germany, for example, can be traced back to traditions already described by the Roman architect Vitruvius.
In the 12th century, bricks from Northern Italy were re-introduced to Northern Germany, where an independent tradition evolved. It culminated in the so-called brick Gothic, a reduced style of Gothic architecture that flourished in Northern Europe, especially in the regions around the Baltic Sea which are without natural rock resources. Brick Gothic buildings, which are built almost exclusively of bricks, are to be found in Denmark, Germany, Poland and Russia. However, bricks were long considered an inferior substitute for natural rock.
During the Renaissance and the Baroque, visible brick walls were unpopular and the Brickwork was often covered with plaster. It was only during the mid-18th century that visible brick walls regained some degree of popularity, as illustrated by the Dutch Quarter of Potsdam, for example.
The transport in bulk of building materials such as bricks over long distances was rare before the age of canals, railways, good roads and large, reliable heavy goods vehicles. Before this time bricks were generally made as close as possible to their point of intended use (it has been estimated that in England in the eighteenth century carrying bricks by horse and cart for ten miles over the poor roads then existing could more than double their price).
The use of brick in construction was not limited solely to regions that lacked stone or other materials suitable for building close at hand, bricks were often used, even in areas where stone was available, for reasons including speed of construction and economy. During the building boom of the nineteenth century in the eastern seaboard cities of Boston and New York, for example, locally made bricks were often used in construction in preference to the brownstones of New Jersey and Connecticut for precisely these reasons. However, bricks were also used in regions that lacked stone and other materials suitable for building, including, for example, much of south-eastern England and The Netherlands, places lacking easily-worked stone but having access to clays suitable for brick making and fuel for firing.
Methods of manufacture
Clay bricks are formed in a mould (the soft mud method), or more frequently in commercial mass production by extruding clay through a die and then wire-cutting them to the desired size (the stiff mud process). Brick made from dampened clay 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 highly resistant to weathering, and thus suitable for facing work. The shaped clay is then dried and fired to achieve the final, desired strength. In modern brickworks, this is usually done in a continuously fired kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistent physical characteristics for all bricks.
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 fuses the slip into a glazed surface integral with the brick base.
Dimensions and strength
For efficient handling and laying bricks must be small enough and light enough to be picked up by the bricklayer using one hand (leaving the other hand free for the trowel). Bricks are usually laid flat and as a result the effective limit on the width of a brick is set by the distance which can conveniently be spanned between the thumb and fingers of one hand, normally about four inches (about 100 mm). In most cases, the length of a brick is about twice its width, about eight inches (about 200 mm). This allows bricks to be laid bonded in a structure to increase its stability and strength (for an example of this, see the illustration of bricks laid in English bond, at the head of this article. The wall is built using alternating courses of stretchers, bricks laid longways and headers, bricks laid crossways. The headers tie the wall together over its width). In England, the length and the width of the common brick has remained fairly constant over the centuries, but the depth has varied from about two inches (about 50 mm) or smaller in earlier times to about two-and-one-half inches (about 65 mm) in more recent times. In the USA modern bricks are usually about 8 x 4 x 2.25 inches (203 x 102 x 57 millimeters) in size. In the UK the usual ("work") size of a modern brick is 215 x 102.5 x 65 mm (about 8.5 x 4 x 2.5 inches) which, with a nominal 10mm mortar joint, forms a "coordinating" or fitted size of 225 x 112.5 x 75 mm (i.e. a ratio of 6:3:2). The compressive strength of bricks produced in the USA ranges from about 1000 lbf/in? to 15,000 lbf/in? (7 to 105 megapascals), varying according to the use to which the bricks are to be put.
Use
Bricks are typically used for building and pavement. In the USA, brick pavement was found incapable of withstanding heavy traffic, but it is coming back into use as a method of traffic calming or as a decorative surface in pedestrian precincts.
Bricks are also used in the metallurgy and glass industries for lining furnaces. They have various uses, especially refractory bricks such as silica, magnesia, chamotte and neutral (chromomagnesite) refractory bricks . This type of brick must have a series of properties such as good thermal shock, resistance, refractoriness under load, high melting point, satisfactory porosity (which can influence several other properties), all of which are high-temperature properties. There is a large refractory brick industry, especially in the UK, Japan and the USA.
In the United Kingdom, bricks have been used in construction for centuries. Until relatively recently, many houses were built almost entirely from red bricks. This use is particularly prevalent in areas of northern England and some outskirts of London, where rows of terraced houses were rapidly and cheaply built to house local workers. These houses have survived to the present day, but some are in need of attention as their structure has deteriorated. Although many houses in the UK are now built using a mixture of breeze blocks and other materials, many houses are skinned with a layer of bricks on the outside for aesthetic appeal.