Brick

A brick is building material used to make walls, pavements and other elements in construction. Traditionally, the term brick referred to a unit composed of, but it is now used to denote rectangular units made of clay-bearing soil, sand, and , or materials. Bricks can be joined together using, adhesives or by ing them. Bricks are produced in numerous classes, types, materials, and sizes which vary with region and time period, and are produced in bulk quantities. Two basic categories of bricks are fired and non-fired bricks.

is a similar term referring to a rectangular building unit composed of similar materials, but is usually larger than a brick. Lightweight bricks (also called lightweight blocks) are made from.

Fired bricks are one of the longest-lasting and strongest s, sometimes referred to as artificial stone, and have been used since circa 4000 BC. Air-dried bricks, also known as s, have a history older than fired bricks, and have an additional ingredient of a mechanical binder such as straw.

Bricks are laid in courses and numerous patterns known as bonds, collectively known as, and may be laid in various kinds of to hold the bricks together to make a durable structure.

Middle East and South Asia
The earliest bricks were dried brick, meaning that they were formed from clay-bearing earth or mud and dried (usually in the sun) until they were strong enough for use. The oldest discovered bricks, originally made from shaped mud and dating before 7500 BC, were found at, in the upper region and in southeast  close to. The n inhabitants of also constructed, and lived in, air-dried  houses between 7000–3300 BC. Other more recent findings, dated between 7,000 and 6,395 BC, come from, , the ancient Egyptian fortress of , and the ancient  cities of , , and. Ceramic, or fired brick was used as early as 3000 BC in early Indus Valley cities like.

China
The earliest fired bricks appeared in Neolithic China around 4400 BC at, a walled settlement of the. These bricks were made of red clay, fired on all sides to above 600 °C, and used as flooring for houses. By the (3300 BC), fired bricks were being used to pave roads and as building foundations at Chengtoushan.

Bricks continued to be used during 2nd millennium BC at a site near. Fired bricks were found in (1046–771 BC) ruins, where they were produced on a large scale. The carpenter's manual , published in 1103 at the time of the described the brick making process and  techniques then in use. Using the 17th-century encyclopaedic text , historian outlined the brick production process of  China: ""...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 labourers 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 standardised 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.""

Europe
Early civilisations around the adopted the use of fired bricks, including the  and. The s operated mobile s, and built large brick structures throughout the, stamping the bricks with the seal of the legion.

During the the use of bricks in construction became popular in, after being introduced there from Northern-Western. An independent style of brick architecture, known as (similar to ) flourished in places that lacked indigenous sources of rocks. Examples of this architectural style can be found in modern-day, , , and.

This style evolved into as the stylistic changes associated with the  spread to northern Europe, leading to the adoption of  elements into brick building. A clear distinction between the two styles only developed at the transition to. In, for example, Brick Renaissance is clearly recognisable in buildings equipped with terracotta reliefs by the artist Statius von Düren, who was also active at  and  (Fürstenhof).

Long-distance of bricks and other construction equipment remained prohibitively expensive until the development of modern transportation infrastructure, with the construction of, s, and s.

Industrial era
Production of bricks increased massively with the onset of the and the rise in factory building in England. For reasons of speed and economy, bricks were increasingly preferred as building material to stone, even in areas where the stone was readily available. It was at this time in that bright red brick was chosen for construction to make the buildings more visible in the heavy fog and to help prevent traffic accidents.

The transition from the traditional method of production known as hand-moulding to a mechanised form of mass-production slowly took place during the first half of the nineteenth century. Possibly the first successful brick-making machine was ed by Henry Clayton, employed at the Atlas Works in, England, in 1855, and was capable of producing up to 25,000 bricks daily with minimal supervision. His mechanical apparatus soon achieved widespread attention after it was adopted for use by the for brick-making at their factory near. The ‘Stiff-Plastic Brickmaking Machine’ was patented in 1853, apparently predating Clayton. Bradley & Craven went on to be a dominant manufacturer of brickmaking machinery. Predating both Clayton and Bradley & Craven Ltd. however was the brick making machine patented by Richard A. Ver Valen of Haverstraw, New York in 1852.

The demand for high office building construction at the turn of the 20th century led to a much greater use of and, and later, steel and. The use of brick for construction severely limited the size of the building – the, built in 1896 in Chicago, required exceptionally thick walls to maintain the structural integrity of its 17 storeys.

Following pioneering work in the 1950s at the and the  in, UK, the use of improved masonry for the construction of tall structures up to 18 storeys high was made viable. However, the use of brick has largely remained restricted to small to medium-sized buildings, as steel and concrete remain superior materials for high-rise construction.

Types
There are thousands of types of bricks that are named for their use, size, forming method, origin, quality, texture, and/or materials.

Categorized by manufacture method:
 * Extruded – made by being forced through an opening in a steel die, with a very consistent size and shape.
 * Wire-cut – cut to size after extrusion with a tensioned wire which may leave drag marks
 * Moulded – shaped in moulds rather than being extruded
 * Machine-moulded – clay is forced into moulds using pressure
 * Handmade – clay is forced into moulds by a person
 * Dry-pressed – similar to soft mud method, but starts with a much thicker clay mix and is compressed with great force.

Categorized by use:
 * Common or building – A brick not intended to be visible, used for internal structure
 * Face – A brick used on exterior surfaces to present a clean appearance
 * Hollow – not solid, the holes are less than 25% of the brick volume
 * Perforated – holes greater than 25% of the brick volume
 * Keyed – indentations in at least one face and end to be used with rendering and plastering
 * Paving – brick intended to be in ground contact as a walkway or roadway
 * Thin – brick with normal height and length but thin width to be used as a veneer

Specialized use bricks:
 * Chemically resistant – bricks made with resistance to chemicals
 * – acid resistant bricks
 * – a type of hard, dense, brick used where strength, low water porosity or acid (flue gas) resistance are needed. Further classified as type A and type B based on their compressive strength
 * – a type of engineering brick from England
 * or refractory – highly heat-resistant bricks
 * – a vitrified brick
 * Ceramic glazed – fire bricks with a decorative glazing

Bricks named for place of origin:
 * – a light yellow brick made in Milwaukee, Wisconsin
 * – a hard light coloured brick originally from the Netherlands
 * – a type of construction brick
 * – type of handmade brick which was used for the majority of building work in London and South East England until the growth in the use of machine-made bricks
 * – a type of decorative brick in India
 * – a long, flat brick typically used by the Romans
 * – a type of construction brick from England

Methods of manufacture
Three basic types of brick are un-fired, fired, and chemically set bricks. Each type is manufactured differently.

Mudbrick
Unfired bricks, also known as s, are made from a wet, clay-containing soil mixed with straw or similar binders. They are air-dried until ready for use.

Fired brick
Fired bricks are burned in a kiln which makes them durable. Modern, fired, clay bricks are formed in one of three processes – soft mud, dry press, or extruded. Depending on the country, either the extruded or soft mud method is the most common, since they are the most economical.

Normally, bricks contain the following ingredients:


 * 1) Silica (sand) – 50% to 60% by weight
 * 2) Alumina (clay) – 20% to 30% by weight
 * 3) Lime – 2 to 5% by weight
 * 4) Iron oxide – ≤ 7% by weight
 * 5) Magnesia – less than 1% by weight

Shaping methods
Three main methods are used for shaping the raw materials into bricks to be fired:


 * Molded bricks – These bricks start with 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 press. The shaped clay is then fired ("burned") at 900–1000 °C to achieve strength.
 * Dry-pressed bricks – The dry-press method is similar to the soft-mud moulded method, 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 – For extruded bricks the clay is mixed with 10–15% (stiff extrusion) or 20–25% water (soft extrusion) in a . This mixture is forced through a  to create a long cable of material of the desired width and depth. This mass is then cut into bricks of the desired length by a wall of wires. Most structural bricks are made by this method as it produces hard, dense bricks, and suitable dies can produce perforations as well. The introduction of such holes reduces the volume of clay needed, and hence the cost. Hollow bricks are lighter and easier to handle, and have different thermal properties from solid bricks. The cut bricks are hardened by drying for 20 to 40 hours at 50 to 150 °C before being fired. The heat for drying is often waste heat from the kiln.

Kilns
In many modern, bricks are usually fired in a continuously fired tunnel kiln, in which the bricks are fired as they move slowly through the kiln on , rails, or kiln cars, which achieves a more consistent brick product. The bricks often have, ash, and organic matter added, which accelerates the burning process.

The other major kiln type is the Bull's Trench Kiln (BTK), based on a design developed by British engineer W. Bull in the late 19th century.

An oval or circular trench is dug, 6–9 metres wide, 2-2.5 metres deep, and 100–150 metres in circumference. 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. Historically, a stack of unfired bricks covered for protection from the weather was called a "hack". Cooled finished bricks are removed from the other end for transport to their destinations. In the middle, the brick workers create a firing zone by dropping fuel (coal, wood, oil, debris, and so on) through access holes in the roof above the trench.

The advantage of the BTK design is a much greater energy efficiency compared with or s. 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 the bricks), and finally out the chimney, where the rising gases create suction that pulls air through the system. The reuse of heated air yields savings in fuel cost.

As with the rail process, the BTK process is continuous. A half-dozen labourers 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.

Influences on colour
The fired colour of tired clay bricks is influenced by the chemical and mineral content of the raw materials, the firing temperature, and the atmosphere in the kiln. For example, pink 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; as the temperature is increased the colour moves through dark red, purple, and then to brown or grey at around 1300 C. The names of bricks may reflect their origin and colour, such as and Cambridgeshire White. Brick tinting may be performed to change the colour of bricks to blend-in areas of brickwork with the surrounding masonry.

An impervious and ornamental surface may be laid on brick either by, in which salt is added during the burning process, or by the use of a , 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.

Chemically set bricks
Chemically set bricks are not fired but may have the curing process accelerated by the application of heat and pressure in an autoclave.

Calcium-silicate bricks
Calcium-silicate bricks are also called sandlime or flintlime bricks, depending on their ingredients. Rather than being made with clay they are made with binding the silicate material. The raw materials for calcium-silicate bricks include lime mixed in a proportion of about 1 to 10 with sand,, crushed , or crushed siliceous rock together with mineral s. The materials are mixed and left until the lime is completely hydrated; the mixture is then pressed into moulds and cured in an for three to fourteen hours to speed the chemical hardening. The finished bricks are very accurate and uniform, although the sharp es need careful handling to avoid damage to brick and bricklayer. The bricks can be made in a variety of colours; white, black, buff, and grey-blues are common, and pastel shades can be achieved. This type of brick is common in Sweden, especially in houses built or renovated in the 1970s. In India these are known as s, manufactured using the FaL-G (fly ash, lime, and gypsum) process. Calcium-silicate bricks are also manufactured in Canada and the United States, and meet the criteria set forth in ASTM C73 – 10 Standard Specification for Calcium Silicate Brick (Sand-Lime Brick).

Concrete bricks
Bricks formed from are usually termed as blocks or, and are typically pale grey. 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 bricks and blocks are manufactured in a wide range of shapes, sizes and face treatments – a number of which simulate the appearance of clay bricks.

Concrete bricks are available in many colours and as an engineering brick made with sulfate-resisting Portland cement or equivalent. When made with adequate amount of cement they are suitable for harsh environments such as wet conditions and retaining walls. They are made to standards BS 6073, EN 771-3 or ASTM C55. Concrete bricks contract or shrink so they need movement joints every 5 to 6 metres, but are similar to other bricks of similar density in thermal and sound resistance and fire resistance.

Compressed earth blocks
s are made mostly from slightly moistened local soils compressed with a mechanical hydraulic press or manual lever press. A small amount of a cement binder may be added, resulting in a stabilised compressed earth block.

Optimal dimensions, characteristics, 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 twice its width plus the width of a mortar joint, about eight inches (about 200 mm) or slightly more. This allows bricks to be laid  in a structure which increases stability and strength (for an example, 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 fact, this wall is built in a variation of English bond called English cross bond where the successive layers of stretchers are displaced horizontally from each other by half a brick length. In true English bond, the perpendicular lines of the stretcher courses are in line with each other.

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 in Gdansk; built in 1571 of imported, 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 specialised insulation materials.

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

In England, the length and width of the common brick has remained fairly constant over the centuries (but see ), 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, the usual size of a modern brick is 215 × 102.5 × 65 mm (about $8 5/8$ × $4 1/8$ × $2 5/8$ inches), which, with a nominal 10 mm ($3/8$ inch) mortar joint, forms a  of 225 × 112.5 × 75 mm (9 × $4 1/2$ × 3 inches), for a ratio of 6:3:2.

In the United States, modern standard bricks are specified for various uses; most are sized at about 8 × $3 5/8$ × $2 1/4$ inches (203 × 92 × 57 mm). The more commonly used is the modular brick $7 5/8$ × $3 5/8$  × $2 1/4$ inches (194 × 92 × 57 mm). This modular brick of $7 5/8$ with a $3/8$ mortar joint eases the calculation of the number of bricks in a given wall.

Some brickmakers create innovative sizes and shapes for bricks used for plastering (and therefore not visible on the inside of the building) where their inherent mechanical properties are more important than their 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
 * Their ribbed exterior aids plastering
 * More complex interior cavities allow improved insulation, while maintaining strength.

Blocks have a much greater range of sizes. Standard co-ordinating 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 2000 kg/m³: this is reduced by frogging, hollow bricks, and so on, 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 "frog" can refer to the indentation or the implement used to make it. Modern brickmakers usually use plastic frogs but in the past they were made of wood.

The compressive strength of bricks produced in the United States ranges from about 1000 lbf/in² to 15,000 lbf/in² (7 to 105 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, although a common house brick is likely to show a range of 20–40.

Use
In the United States, bricks have been used for both buildings and pavements. Examples of brick use in buildings can be seen in colonial era buildings and other notable structures around the country. Bricks have been used in pavements especially during the late 19th century and early 20th century. The introduction of asphalt and concrete reduced the use of brick pavements, but it is used as a method of  or as a decorative surface in. For example, in the early 1900s, most of the streets in the city of, , were paved with bricks. 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). Much like in Grand Rapids, municipalities across the United States began replacing brick streets with inexpensive by the mid-20th century.

Bricks in the and  industries are often used for lining s, in particular  bricks such as, ,  and neutral. This type of brick must have good resistance, refractoriness under load, high melting point, and satisfactory. There is a large refractory, especially in the United Kingdom, Japan, the United States, Belgium and the Netherlands.

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

s are used where strength, low water porosity or acid (flue gas) resistance are needed.

In the UK a is one founded in the late 19th or early 20th century. The term is used to refer to such institutions collectively to distinguish them from the older institutions, and refers to the use of bricks, as opposed to stone, in their buildings.

Colombian architect was noted for his extensive use of red bricks in his buildings and for using natural shapes like spirals, radial geometry and curves in his designs. Most buildings in are made of brick, given the abundance of clay in equatorial countries like this one.

Limitations
Starting in the 20th century, the use of brickwork declined in some areas due to concerns with earthquakes. Earthquakes such as the and the  revealed the weaknesses of unreinforced brick masonry in earthquake-prone areas. During seismic events, the mortar cracks and crumbles, and the bricks are no longer held together. Brick masonry with steel reinforcement, which helps hold the masonry together during earthquakes, was used to replace many of the unreinforced masonry buildings. Retrofitting older unreinforced masonry structures has been mandated in many jurisdictions.