Brick
This page is about clay bricks used for construction. For other uses of the word "brick" please see Brick (disambiguation). |
An old brick wall in English bond laid with alternating courses of headers and stretchers. |
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.
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The brickwork of Shebeli Tower displays 12th century craftsmanship. |
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West face of Roskilde Cathedral in Roskilde, Denmark |
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
ratio of 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.
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/in² to 15,000 lbf/in² (7 to 105
megapascals), varying according to the use to which the bricks are to be put.
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A brick kiln,Tamilnadu, India. The bricks made of clay are dried in open and arranged in a pyramid fashion.The gaps created at the base are used to fill the firewood for baking. |
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
United Kingdom,
Japan and the
U.S.A..
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.
*
Adobe*
Brickwork*
Brickwork bonds*
Ceramics
*
Fire brick*
Masonry*
Mudbrick*
International Union of Bricklayers and Allied Craftworkers*
Brick in 20th-century architecture*
Production process of bricks
