Clay bricks, also called burnt clay, are the oldest structural man-made building material. They have changed little over the millennia, perhaps because they are the perfect size and weight for a mason to lay and manipulate them, one by one, to form a sturdy structure. They are durable to the elements, long-lasting, low maintenance, reusable and do not contain any harmful ingredients.

Bricks are made from fired clay mineral, fillers, fluxes and a certain amount of impurities. The clay is mined from the ground – dug up and stockpiled. They type of clay will affect colour and quality. Popular brick colours include red, white, tan, brown, orange, grey and black. The colour is influenced by the chemical and mineral content of the raw materials, the firing temperature, and the atmosphere in the kiln. For example, whereas red bricks are the result of a high iron (Fe) content, white or yellow bricks have a higher lime content. In the past, bricks would’ve been made from locally-sourced clay, which helped determine the appearance of brick buildings in the area.

The mix may contain recycled material, such as agricultural and industrial waste, or pulverised fuel ash (PFA), which is a by-product of coal-fuelled power stations. As well as reducing the amount of mined material required, waste materials may yield benefits for production (such as lowering firing temperature) or affect the appearance of the finished article.

The shape, surface and performance depend on the ingredients and method of manufacture. Modern bricks are formed from carefully homogenised ingredients to ensure consistent quality, colour and performance. Facing bricks for facades and interiors are shaped by moulding or extrusion; and engineering bricks for more demanding applications are extruded.

Clay brick and concrete block are suitable for many of the same applications. And while brick is typically stronger and lighter than normal strength concrete, the ultimate strength of a wall is largely dependent on the mortar that joins them together. Concrete is available in many different configurations, such as aerated to reduce weight and so permit larger blocks, which reduces the amount of mortar needed. It is also less expensive and more resistant to water and freezing conditions. Bricks are preferred for their appearance, especially over time. Also, bricks do not require the same frequency of movement joints as concrete: 12 m versus 6 m for concrete. This is especially important for low-rise buildings, where clay is unlikely to require a movement joint, but concrete almost certainly will. Without movement joints, the concrete is prone to cracking as it shrinks over time.