Bricks

History of Bricks

Bricks Wall

Archaeologists have found bricks in the Middle East dating 10,000 years ago. Scientists suggest that these bricks were made from mud left after the rivers in that area flooded. The bricks were moulded by hand and left in the sun to dry. Structures were built by layering the bricks using mud and tar as mortar. The ancient city of Ur (modern Iraq) was built with mud bricks around 4,000 B.C. The Bible (Exodus 1:14; 5:4-19) provides the earliest written documentation of brick production—the Israelites made bricks for their Egyptian rulers. These bricks were made of clay dug from the earth, mixed with straw, and baked in crude ovens or burned in a fire. Many ancient structures made of bricks, such as the Great Wall of China and remnants of Roman buildings, are still standing today. The Romans further developed kiln-baked bricks and spread the art of brick making throughout Europe.

The oldest type of brick in the Western Hemisphere is the adobe brick. Adobe bricks are made from adobe soil, comprised of clay, quartz, and other minerals, and baked in the sun. Adobe soil can be found in dry regions throughout the world, but most notably in Central America, Mexico, and the south western United States. The Pyramid of the Sun was built of adobe bricks by the Aztecs in the fifteenth century and is still standing. In North America, bricks were used as early as the seventeenth century. Bricks were used extensively for building new factories and homes during the Industrial Revolution. Until the nineteenth century, raw materials for bricks were mined and mixed, and bricks were formed, by manual labour. The first brick making machines were steam powered, and the bricks were fired with wood or coal as fuel. Modern brick making equipment is powered by gas and electricity. Some manufacturers still produce bricks by hand, but the majority are machine made.

Phases of Manufacturing Bricks

The manufacturing process has six general phases: 

1) mining and storage of raw materials, 

2) preparing raw materials, 

3) forming the brick, 

4) drying, 

5) firing and cooling and 

6) de-hacking and storing finished products.

Mining and Storage 

Surface clays, shales and some fire clays are mined in open pits with power equipment. Then the clay or shale mixtures are transported to plant storage areas.

Preparation

To break up large clay lumps and stones, the material is processed through size-reduction machines before mixing the raw material. Usually the material is processed through inclined vibrating screens to control particle size.

Forming

Tempering, the first step in the forming process, produces a homogeneous, plastic clay mass. Usually, this is achieved by adding water to the clay in a pug mill, a mixing chamber with one or more revolving shafts with blade extensions. After pugging, the plastic clay mass is ready for forming. There are three principal processes for forming brick: stiff-mud, soft-mud and dry-press.

• Stiff-Mud Process - In the stiff-mud or extrusion process, water in the range of 10 to 15 percent is mixed into the clay to produce plasticity. After pugging, the tempered clay goes through a dearing chamber that maintains a vacuum of 15 to 29 in. (375 to 725 mm) of mercury. De-airing removes air holes and bubbles, giving the clay increased workability and plasticity, resulting in greater strength. Next, the clay is extruded through a die to produce a column of clay. As the clay column leaves the die, textures or surface coatings may be. An automatic cutter then slices through the clay column to create the individual brick. Cutter spacings and die sizes must be carefully calculated to compensate for normal shrinkage that occurs during drying and firing.
• Soft-Mud Process - The soft-mud or molded process is particularly suitable for clays containing too much water to be extruded by the stiff-mud process. Clays are mixed to contain 20 to 30 percent water and then formed into brick in molds. To prevent clay from sticking, the molds are lubricated with either sand or water to produce “sand-struck” or “water-struck” brick. Brick may be produced in this manner by machine or by hand.
• Dry-Press Process - This process is particularly suited to clays of very low plasticity. Clay is mixed with a minimal amount of water (up to 10 percent), then pressed into steel molds under pressures from 500 to 1500 psi (3.4 to 10.3 MPa) by hydraulic or compressed air rams.

Drying

Wet brick from molding or cutting machines contain 7 to 30 percent moisture, depending upon the forming method. Before the firing process begins, most of this water is evaporated in dryer chambers at temperatures ranging from about 100 ºF to 400 ºF (38 ºC to 204 ºC). The extent of drying time, which varies with different clays, usually is between 24 to 48 hours. Although heat may be generated specifically for dryer chambers, it usually is supplied from the exhaust heat of kilns to maximize thermal efficiency. In all cases, heat and humidity must be carefully regulated to avoid cracking in the brick.

Hacking

Hacking is the process of loading a kiln car or kiln with brick. The number of brick on the kiln car is determined by kiln size. The brick are typically placed by robots or mechanical means. The setting pattern has some influence on appearance. Brick placed face-to face will have a more uniform colour than brick that are cross-set or placed face-to-back.

Firing

Brick are fired between 10 and 40 hours, depending upon kiln type and other variables. There are several types of kilns used by manufacturers. The most common type is a tunnel kiln, followed by periodic kilns. Fuel may be natural gas, coal, sawdust, and methane gas from landfills or a combination of these fuels.

Cooling

After the temperature has peaked and is maintained for a prescribed time, the cooling process begins. Cooling time rarely exceeds 10 hours for tunnel kilns and from 5 to 24 hours in periodic kilns. Cooling is an important stage in brick manufacturing because the rate of cooling has a direct effect on colour.

De-hacking

De-hacking is the process of unloading a kiln or kiln car after the brick have cooled, a job often performed by robots. Brick are sorted, graded and packaged. Then they are placed in a storage yard or loaded onto rail cars or trucks for delivery. The majority of brick today are packaged in self-contained, strapped cubes, which can be broken down into individual strapped packages for ease of handling on the jobsite. The packages and cubes are configured to provide openings for handling by forklifts. More info of bricks process on following videos:

TYPES OF BRICKS

There are literally thousands of different bricks, but they can be broken down into a handful of basic types. The vast majority are made from clay and are kiln-fired.        

Facing Bricks

It is quality and durable bricks with an attractive appearance for external use above ground. 

Wirecut

The clay is continuously extruded to a required size and shape and then cut into individual bricks by means of a wire; much like a cheese is cut by cheese wire.  There are thousands of variations of blocks in colour and texture. Usually the cheapest facings available as the manufacturing process are highly automated.  

Stock

The clay is wetted to a so-called "soft mud" and then moulded to shape, before being allowed to dry prior to firing in the kiln. Much of the process is automated. Tend to be slightly irregular in shape. It is usually a bit more expensive than wirecuts.

Handmade

Handmade bricks are usually made on a bench, in a mould, much as described above for a stock brick. Because the clay isn't firmly compacted by machine, each brick normally has distinctive creasing known as a 'smile'. It is very desirable, and the most expensive of the facings, but well worth it on prestige jobs. 

Fletton

Also known as 'London Bricks'. A unique facing brick manufactured from the Lower Oxford clay found only in SE England. This clay contains coal traces, which burn during firing, reducing the amount of fuel needed for the kiln, which not only keeps down costs but also produces some interesting effects in the bricks themselves.

Commons

A cheap 'fill' brick, designed to be utilitarian rather than attractive. It is having said that, some have a charm of their own and are perfectly fine for smaller jobs.  

Common Bricks

Engineering

The workhorses of the brick family. Tough, strong, hardwearing but not usually very pretty. They have excellent resistance to frost and to water, making them ideal for ground works, sewer works and retaining walls. You pay for the performance.

Engineered Bricks

Concrete or Calcium Silicate

Popular in areas where good brick-making clay is scarce. Some are, quite frankly, bloody awful, but others may be split-faced or have a pitched face to give an impression of being something other than boring concrete. Cheap and cheerful sums them up.  

Concrete and Calcium Silicate Bricks

Reclaimed

Salvaged bricks. Bricks rescued from old buildings and cleaned up, of a fashion. Their charm is undeniable, when laid by a good brickie, but there can be a high level of wastage. Many will be the old Imperial sizes (2 5/8" or 3") which are incompatible with the modern metric bricks (65mm).

TYPES OF BRICK BONDING

Brickwork can be constructed by various arrangement of bricks bonded to form an integrated structure. There are a few commonly used bond patterns:

• English Bond

Alternative courses of headers and stretchers; one header placed centrally above each stretcher. This is a very strong bond when the wall is 1 brick thick (or thicker)

• English Garden Wall Bond

An alternative version of English bond with header courses being inserted at every fourth or sixth course. This is a correspondingly weaker bond English Garden Wall bond.

• Flemish Bond

Alternate bricks are placed as header and stretcher in every course. Each header is placed centrally between the stretcher immediately above and below. This is not as strong as the English bond at 1 brick thick.

• Flemish Garden Wall Bond

Like English Garden Wall bond, this was originally intended for use in solid walls which were required to be fair faced both sides. The number of stretchers is increased and three stretchers are laid to one header in each course.

• Raking Bond

Herringbone and diagonal bonds can be effective within an exposed framed construction, or contained within restraining brick courses.

• Strecher Bond

Originally used for single brick walls, now called 1/2 brick walls it became the obvious choice for cavity walls as less cutting was required.

BENEFITS OF BRICKS

Bricks of course have been around for centuries proving their long lasting and durability attributes. But there are many other benefits that have stamped bricks as the premier building product for future housing construction. There have been many products that have come and gone after claiming to be worthwhile replacements for bricks.

• Minimal maintenance
• Termite resistant
• Solid, safe, and secure
• Investment
• Environmental sustainability
• Brickwork is cost effective
• Aesthetic qualities
• Thermal mass - warmer in winter, cooler in summer
• Noise Reduction