Bricks, as we know them today are building components formed of clay, concrete, or other similar substance, usually machine made and used in constructing walls.
Bricks were initially used in the early Egyptian dynasties and were formed of alluvial silt. The art of brick-making then passed to the Romans who subsequently developed a characteristic, flat, kiln-burnt brick using sand or clay. Roman bricks still survive in Britain today, as in the tower of St Alban's Abbey.
The basic process in the manufacture of modern clay bricks still consists of 'winning' and preparing the clay, forming it into the required brick shape, and then drying and firing it. Brickmaking has now developed into a highly mechanised industry and takes place in a continuous process in a tunnel kiln, although some expensive bricks may be hand-finished to provide a pleasing appearance. Another method used is the Hoffman kiln whereby the fire is moved around various interconnecting chambers which contain the bricks.
Because bricks are laid manually, it is essential that they be made in sizes that are easily lifted with one hand.
Four major kinds of brick are produced. Common brick, made from clay, is the ordinary brick of commerce. Face brick, made from clay, is used in exposed exterior and interior masonry walls and in architectural applications where the size, color, and texture of the brick are especially important. Common brick and face brick are made in numerous sizes, shapes, surface textures, and colors. Calcium silicate brick, made of sand and lime, is used as building brick and as face brick. Refractory brick, made from clay or nonclay minerals, is used in furnaces.
Common Brick. Any clay that is plastic enough to be shaped and becomes hard and strong when burned at a relatively low temperature in a kiln is suitable for making common brick. Because common brick generally is used as an unexposed backup for face brick, its size and shape, color, and resistance to weathering are less important than for face brick.
Common brick generally has a red color because iron in the clay is converted to iron oxide or other red-colored compounds when the brick is fired. Yellow brick is made by firing clays that have a small amount of iron.
Face Brick. Face brick, which is used only for wall surfaces that are exposed to view or require a decorative effect, must be exact in shape, size, and color. Such brick must also have good weather resistance.
Clays for making face brick, when formed and fired, range in color from red to nearly white, depending on the type of clay used. Colorants can be added to provide an almost complete spectrum of brick colors.
Calcium Silicate Brick. Hydrated lime and sand or pulverized quicklime and sand, in a ratio of 1 part lime to 10 parts sand, are used to make calcium silicate brick (sand-lime brick). This brick is produced in large quantities in Canada, Germany, and the Soviet Union. Sand-lime brick, which is not so strong or durable as clay brick, is made in areas where clay is scarce.
Refractory Brick. Clays or nonclay minerals are used to make refractory bricks for furnace construction where resistance to temperatures as high as 3000° F (1787° C) is required.
Most refractory bricks are made from fireclays, which chiefly contain alumina and silica.
Fireclays have a much greater ability to resist heat than do other clays. Fireclay bricks are used for lining the sides of fireplaces and industrial furnaces.
The two major kinds of nonclay refractory brick are magnesia brick and chrome brick. They are used principally in steelmaking furnaces, glass-melting furnaces, and other industrial furnaces where conditions are severe. Other non-clay refractory materials include silica, alumina, bauxite, zircon (zirconium silicate), zirconia (zirconium oxide), silicon carbide, and dolomite.
In building a straight wall, bricks are laid in horizontal layers. To make sure the wall is straight horizontally, it is built to a line. A plumb line can be used to ensure that the wall is built straight upward.
Mortar is placed between the bricks to form horizontal and vertical joints 0.3 to 1.3 cm thick. The bricks are bedded with mortar to cause the bricks to adhere to one another, to distribute pressure uniformly over the structure, and to make the wall watertight. A trowel is used to apply mortar between the bricks.
When a brick is laid, it should be pressed down into a generous mortar bed and shoved into final position to ensure that (1) the mortar is forced into the spaces between the brick; (2) the horizontal and vertical joints are filled with mortar; and (3) the wall will be watertight.
In brickwork, an arrangement of bricks is
called a bond. A brick laid so that its long side is exposed to view is
called a stretcher; a brick that is laid with its end exposed is called
a header. Different arrangements of headers and stretchers make the
different kinds of bonds. Various arrangements are used; some of the
more commonly used ones may be found in the accompanying diagrams.
- RUNNING (or STRETCHER) bond is laid in overlapping courses of stretchers (bricks' long sides).
- FLEMISH bond has the headers (short sides) and stretchers alternately laid in every course.
- CHECKER bond is a checkerboard pattern of headers primarily used for decorative purposes.
- ENGLISH bond has the vertical mortar joint one third from the end of each stretcher brick.
- BASKETWEAVE, used for paving, may be laid flat or on edge or may be a combination of both.
- GARDEN WALL, a strong bond, has a symmetrical placing of the headers in every other course.
- COMMON (HEADER) bond, the most com mon bond, has a series of headers breaking each sixth row.
- ENGLISH (DUTCH) CROSS has stretcher joints overlapping half a length in alternating rows.
- STACKED bond, popular for facing buildings, is laid with the stretchers in vertical lines.
- HERRINGBONE bond, used in paving or paneling, may be laid with the brick flat or on edge.
- RUNNING HEADER is the same as running bond but with headers used instead of the stretchers.
- COMMON (FLEMISH) bond, a modified common bond, has the Flemish bond in the sixth row.
Bricks are widely used today, and indeed for constructions of up to
four storeys brick is a very economic material. Furthermore, bricks
possess good fire and thermal insulation properties and require little
maintenance. The particular qualities of different bricks vary
according to their type and grading, but they are all in general
resistant to chemical pollution. Resistance to frost attack is more
variable. Good bricks should be reasonably hard and strong.
Bricks are usually graded into three categories: (1) internal quality bricks, known as 'commons', which are strong enough for load-bearing walls, but are not suitable for facing work; (2) 'facings' which are manufactured with particular regard to appearance, strength, and other qualities; and (3) ordinary quality or 'stock' quality, from which many buildings are built. A further category of bricks are the special or engineering bricks (and semi-engineering). These are especially hard and are used for carrying exceptional loads (e.g., bridges and piers).
Bricks are further divided into different varieties according to the composition of the clay used. The most important types used are: (1) Flettons which are produced from Oxford clay, of which there are extensive and thick beds. This is used for manufacturing the cheapest types of brick. They are usually a light pinky colour and fairly hard and strong. (2) Marls, produced from sandy clays, are widely used in the Midlands. They may be used as 'facing' bricks and vary in colour from light to dark red. (3) London Stock bricks, which are slightly yellow and contain sand and alumina and some chalk, are common in the south-east England. They have the advantages of being fairly cheap and of weathering very well.