How It’s Made: Clay Brick

Words: Mat Tramel
Photos: ACME Brick

Going back to around 7000 B.C., when the first bricks were made from a combination of mud and straw (highlighted because mud and straw are not part of the defined parameters of masonry) and then dried in the desert sun, the general process of how brick is made has not changed much at all. Around 3500 B.C., the process evolved with the first firing of brick in a kiln following drying. Since then, little to nothing has changed. The process of making brick still starts with a combination of clays taken from the ground. Bricks are then shaped, stacked, dried, fired, and stored for later use. This is how it has always been and continues to be. However, moving into the second quarter of the 21st century, what has changed is how the bricks are shaped, stacked, dried, fired, and stored. Modernization of equipment has made brick-making much more efficient in just about every way possible. While the same principles and processes exist for how brick is made in the 21st century as for when they were first made around 7000 B.C., the quality, colors, durability, and sustainability of brick in the present is the best it has ever been and is expected to continue to improve.

Raw Materials
How brick is made starts with the raw materials. Bricks are made of a combination of clays mixed with water. In many cases, sand and/or recycled/partially fired brick (grog/calcine) are also part of the mix. This mix will have plasticity to allow it to be shaped and stacked with the appropriate wet and air-dried strength to maintain their shape. The clays and often the sands are mined in open pits and then either stockpiled at the mine site, stockpiled at the brick-making location, and/or stored in covered sheds. Materials are then run through a series of size-reducing machines, followed by a run through size-determining screens to ensure that the particle size for the mix is ideal for the next step in the process.

Manufacturing
The manufacturing portion of how brick is made has changed over time mostly by the percentage of brick made in each of three distinct processes. In the earliest days, all the brick was certainly made by hand, which is a process that evolved over time into a soft mud or “molding” process that is done by machine to look like handmade brick. Handmade brick still exists but is a very small percentage of brick made in the 21st century. Nearly all the brick made today is made by a stiff mud extrusion process. The raw material mix is run through additional mixing with additional water added and then extruded using a vacuum process that produces strong, consistently shaped, and consistently sized brick. This is also the point in the process where additional materials would be added to the mix to affect the color of the body of the brick. The natural color of the brick depends on the percentage of various oxides present in the raw materials. The most common of these that affect color are iron (red), magnesium (brown), and calcium (buff/off-white). To change or further enhance the color of the body of the brick, extra oxides are added to the mix.

Color/Appearance
It is between when the bricks are formed and when they are stacked that the color and appearance of the surface of the brick can be affected. Texture, coatings, and/or glazes can be applied. Liquid mixes, known as both slurries and engobes, can be applied to the surface of the brick. These are usually applied in bulk to the brick surface and then distributed with some type of roller or air moving device. Sand mixes (sand is highlighted as it is not primarily within the MCAA definition for masonry) can also be applied to the surface. These are usually rolled into the brick directly with a steel or plastic roller. Both the liquid and sand mixes are made up of a combination of clays, sands, and oxides, fluxes that help them to stick to the surface, and in the case of slurries and engobes, deflocculants, which help to keep the ingredients in the mix in suspension for a consistent appearance. You can develop a mixture to apply virtually any color to the surface of a brick.

Stacking/Setting
How brick is made began to really evolve in the 21st century in this phase of the process. While the bricks themselves are not any different in the majority of cases, how the bricks are stacked or set is much different. From the earliest days, bricks were stacked/set by hand, and there are still a notable portion of brick currently being manufactured that are set by hand, especially those that are still handmade. Those bricks often must be set individually on racks or metal sticks and dried more gently as they need to develop strength before being set. However, the large majority of bricks are now set by automated equipment onto large kiln cars often containing 15–20K bricks per car, with the current machinery involving the latest in 21st century robotics.

Brick in the process of being set on a modern kiln car (Acme Brick – Bennett Plant)

Finished Setting of Brick on a Modern Kiln Car (Acme Brick – Elgin New Plant)

Drying/Firing
Depending on the method that bricks are manufactured, they will be dried beginning at temperatures as low as ambient temperature with extremely high humidity and gradually raised up to temperatures as high as 500 F, meaning no humidity. Most bricks dry in 24 to 48 hours. Once dried, the bricks are fired. In most cases, this is done in a tunnel kiln, in which the kiln cars move automatically. There are some bricks that are still fired in periodic kilns, which are loaded and unloaded manually. Firing temperatures for brick can be as low as 1750 F and as high as 2250 F. Most bricks are fired in 12 to 48 hours. The drying and firing schedules are determined by the raw materials and how to achieve the best quality with each mix.

Brick being fired in a tunnel kiln at around 2000 degrees F (Acme Brick)

Unloading (Dehacking)/Storing
How brick is made continues to evolve in the 21st century in this phase of the process as well. From the earliest days, bricks were unloaded and packaged by hand, and there is still a notable portion of brick currently being handled this way. However, the large majority of bricks are now unloaded by automated equipment from the previously mentioned large kiln cars often containing 15–20K bricks each. These devices are known as dehackers, a modern-day brick/tile term that simply means a machine that unloads kiln cars and stacks bricks/tiles for packaging. After being “dehacked,” bricks are packaged into cubes and then stacked and stored until they are shipped to a job.

Example of NEW modern dehacker (Acme Brick – Denton Plant)

Another example of NEW modern dehacker (Acme Brick – Bennett Plant)

How It’s Made: Clay Brick

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