Brick: Map

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An old brick wall in English bond laid with alternating courses of headers and stretchers.

A brick is a block of ceramic material used in masonry construction, usually laid using mortar.

History

The oldest shaped bricks found date back to 7,500 B.C. They have been found in Çayönü, in the upper Tigris region, and in south east Anatolia close to Diyarbakir. Other more recent findings, dated between 7,000 and 6,395 B.C., come from Jericho

and Catal Hüyük

. From archaeological evidence, the invention of the fired brick (as opposed to the considerably earlier sun-dried mud brick) is believed to have arisen in about the third millennium BC. Being much more resistant to cold and moist weather conditions, brick enabled the construction of permanent buildings in regions where the harsher climate precluded the use of mud bricks. Bricks have the added warmth benefit of storing heat energy from the sun during the day and continuing to release heat after sunset.

Examples of the civilizations who used mudbrick are the ancient Egyptians and the Indus Valley Civilization, where it was used exclusively. In particular, it is evident from the ruins of Buhen, Mohenjo-daro

and Harappa

In Sumerian times offerings of food and drink were presented to "the Bone god," who was "represented in the ritual by the first brick." More recently, mortar for the foundations of the Hagia Sophia

in Istanbul was mixed with "a broth of barley and bark of elm" and sacred relics, accompanied by prayers, placed between every 12 bricks.

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 pre-modern China, brick-making was the job of a lowly and unskilled artisan, but a kiln master was respected as a step above the latter. Early descriptions of the production process and glazing techniques used for bricks can be found in the Song Dynasty carpenter's manual Yingzao Fashi, published in 1103 by the government official Li Jie, who was put in charge of overseeing public works for the central government's construction agency. The historian Timothy Brook writes of the production process in Ming Dynasty

China (aided with visual illustrations from the Tiangong Kaiwu encyclopedic text published in 1637):

...the kilnmaster had to make sure that the temperature inside the kiln stayed at a level that caused the clay to shimmer with the colour of molten gold or silver. He also had to know when to quench the kiln with water so as to produce the surface glaze. To anonymous laborers fell the less skilled stages of brick production: mixing clay and water, driving oxen over the mixture to trample it into a thick paste, scooping the paste into standardized wooden frames (to produce a brick roughly 42 cm long, 20 cm wide, and 10 cm thick), smoothing the surfaces with a wire-strung bow, removing them from the frames, printing the fronts and backs with stamps that indicated where the bricks came from and who made them, loading the kilns with fuel (likelier wood than coal), stacking the bricks in the kiln, removing them to cool while the kilns were still hot, and bundling them into pallets for transportation. It was hot, filthy work.

The idea of signing the worker's name on the brick and the place where it was made was not new to the Ming era and had little or nothing to do with vanity. As far back as the Qin Dynasty (221 BC–206 BC), the government required blacksmiths and weapon-makers to engrave their names onto weapons in order to trace the weapon back to them, lest their weapons should prove to be of a lower quality than the standard required by the government.

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

.

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 sponge over long distances was rare before the age of canals, railways, roads and heavy goods vehicles. Before this time bricks were generally made close 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 (16 km) over the poor roads then existing could more than double their price.

Bricks were often used, even in areas where stone was available, for reasons of speed and economy. The buildings of the Industrial Revolution in Britain were largely constructed of brick and timber due to the demand created. 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 these reasons.

The trend of building upwards for offices that emerged towards the beginning of the 19th century displaced brick in favour of cast and wrought iron and later steel and concrete. Some early 'skyscrapers' were made in masonry, and demonstrated the limitations of the material - for example, the Monadnock Building

in Chicago (opened in 1896) is masonry and just seventeen stories high, the ground walls are almost thick, clearly building any higher would lead to excessive loss of internal floor space on the lower floors. Brick was revived for high structures in the 1950s following work by the Swiss Federal Institute of Technology and the Building Research Establishment

in Watford

, UK. This method produced eighteen story structures with bearing walls no thicker than a single brick (150–225 mm). This potential has not been fully developed because of the ease and speed in building with other materials, in the late-20th century brick was confined to low- or medium-rise structures or as a thin decorative cladding over concrete-and-steel buildings or for internal non-load bearing walls.

Methods of manufacture

Brick making at the beginning of the 20th century.

Bricks may be made from clay, shale, soft slate, calcium silicate, concrete, or shaped from quarried stone.

Clay is the most common material, with modern clay bricks formed in one of three processes - soft mud, dry press, or extruded.

In 2007 a new type of brick was invented, based on fly ash, a by-product of coal power plants.

Mud bricks

The soft mud method is the most common, as it is the most economical. It starts with the raw clay, preferably in a mix with 25-30% sand to reduce shrinkage. The clay is first ground and mixed with water to the desired consistency. The clay is then pressed into steel moulds with a hydraulic press. The shaped clay is then fired ("burned") at 900-1000 °C to achieve strength.

Rail kilns

In modern brickworks, this is usually done in a continuously fired tunnel kiln, in which the bricks move slowly through the kiln on conveyors, rails, or kiln cars to achieve consistency for all bricks. The bricks often have added lime, ash, and organic matter to speed the burning.

Bull's Trench Kilns

In India

, brick making is typically a manual process. The most common type of brick kiln in use there are Bull's Trench Kiln (BTK), based on a design developed by British engineer W. Bull in the late nineteenth century.

An oval or circular trench, 6-9 meters wide, 2-2.5 meters deep, and 100-150 meters in circumference, is dug. A tall exhaust chimney is constructed in the centre. Half or more of the trench is filled with "green" (unfired) bricks which are stacked in an open lattice pattern to allow airflow. The lattice is capped with a roofing layer of finished brick.

In operation, new green bricks, along with roofing bricks, are stacked at one end of the brick pile; cooled finished bricks are removed from the other end for transport. In the middle the brick workers create a firing zone by dropping fuel (coal, [wood], oil, debris, etc) through access holes in the roof above the trench.

The advantage of the BTK design is a much greater energy efficiency compared with clamp or scove kilns. Sheet metal or boards are used to route the airflow through the brick lattice so that fresh air flows first through the recently burned bricks, heating the air, then through the active burning zone. The air continues through the green brick zone (pre-heating and drying them), and finally out the chimney where the rising gases create suction which pulls air through the system. The reuse of heated air yields savings in fuel cost.

As with the rail process above, the BTK process is continuous. A half dozen laborers working around the clock can fire approximately 15,000-25,000 bricks a day. Unlike the rail process, in the BTK process the bricks do not move. Instead, the locations at which the bricks are loaded, fired, and unloaded gradually rotate through the trench.

Dry pressed bricks

The dry press method is similar to mud brick but starts with a much thicker clay mix, so it forms more accurate, sharper-edged bricks. The greater force in pressing and the longer burn make this method more expensive.

Extruded bricks

With extruded bricks the clay is mixed with 10-15% water (stiff extrusion) or 20-25% water (soft extrusion). This is forced through a die to create a long cable of material of the proper width and depth. This is then cut into bricks of the desired length by a wall of wires. Most structural bricks are made by this method, as hard dense bricks result, and holes or other perforations can be produced by the die. The introduction of holes reduces the needed volume of clay through the whole process, with the consequent reduction in cost. The bricks are lighter and easier to handle, and have thermal properties different from solid bricks. The cut bricks are hardened by drying for between 20 and 40 hours at 50-150 °C before being fired. The heat for drying is often waste heat from the kiln.

Calcium silicate bricks

The raw materials for calcium silicate bricks include lime mixed with quartz, crushed flint or crushed siliceous rock together with mineral colourants. The materials are mixed and left until the lime is completely hydrated, the mixture is then pressed into moulds and cured in an autoclave for two or three hours to speed the chemical hardening. The finished bricks are very accurate and uniform, although the sharp arrises need careful handling to avoid damage to brick (and brick-layer). The bricks can be made in a variety of colours, white is common but pastel shades can be achieved.

It is very common in Sweden, especially in houses built or renovated in the '70s. Here it is referred to as "Mexitegel" (en: Mexi[can] Bricks).

Influence on fired colour

The fired colour of clay bricks is influenced by the chemical and mineral content of raw materials, the firing temperature and the atmosphere in the kiln. For example pink coloured bricks are the result of a high iron content, white or yellow bricks have a higher lime content. Most bricks burn to various red hues, if the temperature is increased the colour moves through dark red, purple and then to brown or grey at around . Calcium silicate bricks have a wider range of shades and colours, depending on the colourants used. The names of bricks may reflect their origin and colour, such as London Red and Cambridgeshire White.

Bricks formed from concrete are usually termed blocks, and are typically pale grey in colour. They are made from a dry, small aggregate concrete which is formed in steel moulds by vibration and compaction in either an "egglayer" or static machine. The finished blocks are cured rather than fired using low-pressure steam. Concrete blocks are manufactured in a much wider range of shapes and sizes than clay bricks and are also available with a wider range of face treatments - a number of which are to simulate the appearance of clay bricks.

An 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.

Natural stone bricks are of limited modern utility, due to their enormous comparative mass, the consequent foundation needs, and the time-consuming and skilled labour needed in their construction and laying. They are very durable and considered more handsome than clay bricks by some. Only a few stones are suitable for bricks. Common materials are granite, limestone and sandstone. Other stones may be used (e.g. marble, slate, quartzite, etc.) but these tend to be limited to a particular locality.

Optimal dimensions, characteristics, and strength

Loose bricks

For efficient handling and laying bricks must be small enough and light enough to be picked up by the rocklayer 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) or slightly more. 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.

A bigger brick makes for a thicker (and thus more insulating) wall. Historically, this meant that bigger bricks were necessary in colder climates (see for instance the slightly larger size of the Russian brick in table below), while a smaller brick was adequate, and more economical, in warmer regions. A notable illustration of this correlation is the Green Gate

in Gdansk; built in 1571 of imported Dutch brick, too small for the colder climate of Gdansk, it was notorious for being a chilly and drafty residence. Nowadays this is no longer an issue, as modern walls typically incorporate specialized insulation materials.

The correct brick for a job can be picked from a choice of colour, surface texture, density, weight, absorption and pore structure, thermal characteristics, thermal and moisture movement, and fire resistance.

Face brick ("house brick") sizes, from small to large
Standard	Imperial	Metric
	8 × 4 × 2¼ inches	203 × 102 × 57 mm
	8½ × 4 × 2½ inches	215 × 102.5 × 65 mm
	8¾ × 4 × 3 inches	222 × 106 × 73 mm
	9 × 4⅓ × 3 inches	230 × 110 × 76 mm
		250 × 120 × 65 mm

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 51 mm) or smaller in earlier times to about two and a half inches (about 64 mm) more recently. In the United States

, modern bricks are usually about 8 × 4 × 2.25 inches (203 × 102 × 57 mm). In the United Kingdom

, the usual ("work") size of a modern brick is 215 × 102.5 × 65 mm (about 8.5 × 4 × 2.5 inches), which, with a nominal 10 mm mortar joint, forms a "coordinating" or fitted size of 225 × 112.5 × 75 mm, for a ratio of 6:3:2.

Some brickmakers create innovative sizes and shapes for bricks used for plastering (and therefore not visible) where their inherent mechanical properties are more important than the visual ones. These bricks are usually slightly larger, but not as large as blocks and offer the following advantages:

a slightly larger brick requires less mortar and handling (fewer bricks) which reduces cost
ribbed exterior aids plastering
more complex interior cavities allow improved insulation, while maintaining strength.

Blocks have a much greater range of sizes. Standard coordinating sizes in length and height (in mm) include 400×200, 450×150, 450×200, 450×225, 450×300, 600×150, 600×200, and 600×225; depths (work size, mm) include 60, 75, 90, 100, 115, 140, 150, 190, 200, 225, and 250. They are usable across this range as they are lighter than clay bricks. The density of solid clay bricks is around 2,000 kg/m³: this is reduced by frogging, hollow bricks, etc.; but aerated autoclaved concrete, even as a solid brick, can have densities in the range of 450–850 kg/m³.

Bricks may also be classified as solid (less than 25% perforations by volume, although the brick may be "frogged," having indentations on one of the longer faces), perforated (containing a pattern of small holes through the brick removing no more than 25% of the volume), cellular (containing a pattern of holes removing more than 20% of the volume, but closed on one face), or hollow (containing a pattern of large holes removing more than 25% of the brick's volume). Blocks may be solid, cellular or hollow

The term "melfrog" for the indentation on one bed of the brick is a word that often excites curiosity as to its origin. The most likely explanation is that brickmakers also call the block that is placed in the mould to form the indentation a frog. Modern brickmakers usually use plastic frogs but in the past they were made of wood. When these are wet and have clay on them they resemble the amphibious kind of frog and this is where they got their name. Over time this term also came to refer to the indentation left by them.[Matthews 2006]

Vault of Roman Bath in Bath - England

The compressive strength of bricks produced in the United States ranges from about 1000 lbf/in² to 15,000 lbf/in² (7 to 105 MPa or N/mm² ), varying according to the use to which the brick are to be put. In England clay bricks can have strengths of up to 100 MPa, although a common house brick is likely to show a range of 20–40 MPa.

Use

Bricks are 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. For example, in the early 1900s, most of the streets in the city of Grand Rapids

, Michigan

were paved with brick. Today, there are only about 20 blocks of brick paved streets remaining (totalling less than 0.5 percent of all the streets in the city limits).

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 good thermal shock resistance, refractoriness under load, high melting point, and satisfactory porosity. There is a large refractory brick industry, especially in the United Kingdom

, Japan

and the United States

.

In the United Kingdom, bricks have been used in construction for centuries. Until recently, almost all houses were built almost entirely from bricks. Although many houses in the UK are now built using a mixture of concrete blocks and other materials, many houses are skinned with a layer of bricks on the outside for aesthetic appeal.

In the UK a redbrick university is one founded and built in the Victorian era, often as a technical college. The term is used as differentiation from older, more classics-oriented universities.