Bricks are blocks of clay that have been hardened through being fired in a kiln or dried in the sun. Over time, kiln-fired bricks have grown more popular than sun-dried bricks, although both are still found worldwide. Bricks have been in continual use for around 5000 years, and brickwork from this time still stands in the Middle East, a testament to its durability.
The Roman Legions first brought bricks to Britain, using mobile kilns to construct roads, aqueducts and buildings across the country. Bricks were especially favoured in the 18th and 19th Centuries, although their use has declined over the last 50 years due to the increased availability of cement and concrete.
Manufacture of Bricks
In the past, bricks came in many different shapes and sizes, but today’s modern bricks tend to be a standard size of around 8″ x 4″ x 2″. They demonstrate a wide variety of textures, colours and finishes from yellows, reds and purples, to smooth, rough and rustic. These are due to the mineral variations found in the clay, and the method of manufacturing.
Bricks are traditionally manufactured by mixing clay with enough water to form a mud that is then poured into a mould of the desired shape and size, and hardened through fire or sun. Adobe bricks, very fashionable in parts of the USA, are still made in this way with a mixture of clay and sand (and sometimes manure and straw) being poured into a form, and then removed and dried in stacks outside in the sun.
Compressed Earth Blocks (CEBs) were developed in the 1950s and are similar to adobe bricks, except they are more compact and uniform. They are manufactured from soil that is more sand than clay, and compressed using a manual or motorised machine to produce a variety of block shapes, including hollow designs for insulation. CEBs are highly energy efficient using up to 15 times less energy than a fired brick. They are durable, ecological, inexpensive, and utilise low technology. For this reason they are increasingly used in developing countries as a sustainable building technology.
Modern methods of brick manufacture are highly mechanised and automated procedures whereby clay is extruded in a continuous column, wirecut into bricks, and hydraulically pressed to ensure resistance to weathering. The bricks are then dried and slow fired at around 1000 – 1200° C. In more recent times, recycled glass and other waste materials have been introduced into this process. These materials have been found to reduce firing times, temperatures and toxic emissions, improve brick strength and durability, and reduce waste going to landfill.
Bricks are laid flat in rows called courses, exposing either their sides (stretcher) or ends (header). The pattern of overlap created by the course is called a bond. There are several different kinds of bonds, including Stretcher (most common), Herringbone, English, Basket and Flemish. With all bonds, the vertical joints between each course of bricks must not line up or the structure will be weakened.
Bricks are usually held together by mortar, though some bricks such as CEBs can be dry stacked. Mortar consists of sand, a binding agent (traditionally lime but these days more often cement) and water, which is then mixed to a thick paste. It is applied to a brick, which is then placed onto another brick and allowed to dry. Pointing refers to the visible edge of the mortar between the bricks, which is finished with a special trowel to provide a decorative look to the brickwork.
When building a structure, a bed of mortar is laid on top of the foundation, and the structure’s ends are built up first. A string is then stretched between these ends to ensure each row of bricks stays level. Two layers of brick are used to create a stronger structure, with a gap left in between for insulation purposes. A wide range of structures including arches can be built using bricks.
Bricks as a Sustainable Building Material
Bricks are a versatile and durable building and construction material, with good load-bearing properties, high thermal mass and potential low energy impact. In the case of simple earth bricks such as adobe and CEBs, they measure high on the sustainability index, being made from locally available (and abundant) materials of clay, sand, and water, using low technology compression equipment, solar energy or kilns. While modern methods of brick construction have a much lower sustainability index, the UK brick industry has developed a strategy to minimise its environmental impact and increase its energy efficiency and use of renewable energies. Overall, bricks are a good example of a sustainable building practice and are currently gaining in popularity around the world.