What Are Bricks Made Of? The Materials of Brick Production Explained
Bricks are made of a wide range of materials depending on the availability of materials, regional preferences, and specific location requirements such as building codes and architectural designs. The composition of a particular type of brick will produce a specific look and style as well as define the type of use suited to certain bricks.
The most common ingredients in bricks are clay, sand, water, and additional additives. Yet, not all bricks are equal in substance. Understanding the differences in a brick’s composition will make you more able to assess the quality of a brick type, compare and contrast different bricks, and consider the aesthetics of specific brick styles.
Contents in Brick Production
The contents of bricks differ by region due to the availability of materials, production capacity, innovation level, and architectural needs.
Clay
Clay is the most prominent material in most common bricks because it is found throughout the world. Clay is a fine-grained soil with strong cohesion which means that it holds its shape when it is molded and compressed. Clay is composed of many different minerals and other materials that determine its distinct properties. Together these ingredients determine the clay’s plasticity, shrinkage, strength, and color. Common minerals in clay are kaolinite, illite, and montmorillonite. Other ingredients of clay include silica, alumina, iron oxide and lime.
Popular Clay Varieties for Brick Production
- Kaolin Clay – Kaolin, also known as china clay, is a pure form of clay composed primarily of the mineral kaolinite. It has a fine particle size, white color, and plasticity. Manufacturers use kaolin clay to make high-quality, light-colored bricks and ceramics.
- Fire Clay – Fire clay is a clay that contains alumina and iron oxide. Fire clay has refractory qualities that make it able to withstand high temperatures. Fire clay is a common ingredient in refractory bricks, also called fire bricks.
- Sandy Clay – Sandy clay contains a significant amount of sand mixed with the clay. This clay has excellent plasticity. Sandy clay produces strong bricks with little loss from shrinkage.
Shale
Shale is a fine-grained, laminated, sedimentary rock. Shale, like clay, is a readily abundant natural material. Manufacturers grind up pieces of shale and mix them with clay to form bricks. Shale rock adds iron to the brick mixture to strengthen it, decrease moisture absorption, and increase its abrasion resistance. Shale bricks are best where they will not be subject to thermal shocks.
Fly Ash
Fly ash is a coal combustion product that is used in the manufacturing of bricks. Many people consider fly ash bricks more environmentally friendly than clay bricks. This is because fly ash bricks utilize an industrial waste product and they are self-cementing so the production is more energy-efficient. Fly ash bricks are lighter and stronger than many clay bricks.
Concrete
Concrete bricks, also known as concrete blocks or concrete masonry units (CMU), are made from concrete, an aggregate like sand or mixed stone, and water. Concrete bricks are prized for their stability and durability. Builders utilize concrete bricks in foundations and other load-bearing walls. Most people do not consider concrete bricks an aesthetic choice.
Sand-Lime
Sand-lime bricks, also called calcium silicate bricks, consist of a mixture of sand, lime, and water. Fabricators make sand-lime bricks by using pressure to mold them and then curing them through a chemical reaction called carbonation. Sand-lime bricks have a uniform color and texture. While they have excellent properties of strength and require less mortar, sand-lime bricks do not hold up to water over long periods.
Autoclaved Aerated Concrete
Autoclaved aerated concrete (ACC) is a lightweight, foam concrete building material used to make concrete masonry units (CMU) or bricks. This material is unlike standard concrete because it does not use any aggregate larger than sand. This is an excellent material for structural support. ACC is a material with significant thermal efficiency, so it works well in areas with extreme temperatures.
Compressed Earth
Earth and sand mixed with cement binders are used to form compressed earth blocks or bricks (CEBs). Architects and engineers who favor sustainable and environmentally friendly design value CEBs because of the abundance of soil as a raw material.
Stone
Stone bricks are cut from existing stone rather than molded into a standardized shape. Sandstone is a popular stone for making bricks because fabricators can cut and shape it into blocks. These bricks have a wide range of colors including brown, gray, green, beige, pale yellow, and pink.
Recycled Materials
Innovation in the building industry has allowed for the use of new materials in the construction of bricks. Bricks are now made of recycled products such as crushed concrete, recycled glass, and even plastic waste. These bricks help reduce waste and conserve other primary materials.
Additives
Along with the primary materials like clay, shale, or concrete, fabricators mix in additives that enhance brick performance and change its appearance.
- Plasticizers – Plasticizers like cellulose derivatives and starch are common in brick mixtures to help increase moisture retention and make the material easier to shape and mold.
- Binders – Brick manufacturers use binders to help hold the shape of the brick during the shaping and firing process. Historic binders were gypsum and lime. A common binder today is cement.
- Fluxes – Flux agents are added to the brick material to lower the melting point of the clay minerals. Fluxes promote vitrification and increase the bonding between materials. Common flux materials are feldspar, limestone, and dolomite.
- Coloring agents – Coloring agents, like dyes, change the color of the brick. Coloring agents are both natural and synthetic. Iron oxide is a coloring agent that produces the color red or brown. Chromium oxide produces green colors.
- Stabilizers – Stabilizers increase the dimensional stability of the brick and to reduce shrinkage, warping and cracking during the firing process.
- Antioxidants or anti-efflorescence agents – The presence of these agents in the brick mixture prevents the formation of white crystalline deposits, like salt, on the bricks. This helps to preserve the appearance and the structural integrity of the bricks over time.