process of clay brick making

Clay preparation

Tempering

Tempering is adding water to the clay soil in order to make it more workable. Too much water added to the clay mix will decrease quality, though.

Disintegration and Crushing

An alternative to tempering is disintegration or weathering, which involves allowing clay to dry in the sun and accept moisture from rain and dew. The repeated drying and moistening of clay will bring clay to a plasticity and workability appropriate for brickmaking. Crushing will make the mixture more homogeneous.

Mixing

Mixing is done to make the clay soil homogeneous and smooth. There are different techniques that can be used to do this, including using animal power or letting humans mix the clay with their feet. Different admixtures such as coal or sawdust can be added to the clay for two beneficial reasons: 1) reduce cracking during drying and 2) reduce fuel usage during firing.

Importance of Standardizing the Brickmaking Process

Bricks should have standard characteristics if they are to be used in construction. For example, contractors may buy bricks from several different sources for one project: the bricks must be the same size or there will be problems matching the construction of different sections of the building. Moreover, a standard brick size will allow a contractor to more accurately determine how many bricks will be needed for a project. A new brickmaker, therefore, should follow local standards, checking with other brickmakers in the area or with local authorities or construction contractors.

Shrinkage

When determining the size of a mold for brickmaking, a necessary consideration must be shrinkage. Bricks will shrink when drying, so the mold size must be larger than the intended finished brick.

Slop Molding

In slop molding, a wet clay mixture is used- the mix is put into a rectangular form without a top or bottom. A problem with this technique is that because the mix is so wet, the brick may deform under its own weight and the surface can be marked easily.

Sand Molding

Sand molding utilizes a drier clay mix, formed into a wedge and thrown into a mold. A bow cutter will be used to smooth the top of the brick, and the form will can be released because of a hinged bottom. Since the clay is drier, the brick can be moved with wooden palettes which can reduce the amount of surface marks. There are multiple benefits to using sand molding instead of slop molding, such as:

• Less water is used, so there is less cracking and the bricks are stronger.
• Fewer molds are needed because they can be removed from the brick right away.
• The work space is cleaner because of less splashing of the drier mix.
• The worker is standing up instead of squatting down, so they are more comfortable.
• The bricks are more regular because they don't deform like slop molded bricks, so a better product is produced. Therefore, better construction and better looking buildings will be possible.
• Slop molded bricks can be imprinted with the brickmaker's name, called a "frog," on the flat side of the brick. This helps the brick dry and fire better, and is a good form of advertising.

Water was added during clay preparation to increase workability of the mixture, but in drying it is removed for several reasons. First, there will be less cracking in fired bricks with less water content. Second, additional fuel is needed, beyond what is used for firing, to dry the bricks in the kiln. Proper drying of bricks will involved rotating the bricks for different exposures to ensure even drying rates.

For best results, drying should be done slowly. This will help with more even drying. Also, the best drying technique may change from location to location, so the brickmakers must gain experience to determine the best way to dry bricks for each production process.

Firing

Laying out and constructing a clamp

A clamp is a field kiln built from the green bricks that will be fired. Clamps vary with size and shape and must be oriented with respect to wind direction. Once a clamp is laid out and constructed, it must be insulated.

Finally, the process of firing the clamp will take place in several steps. First, pre-heating, or water-smoking, will remove the water leftover from the drying process. This process is still physical. The second stage is firing, where the clay bricks will vitrify through a chemical process. The temperature must remain constant at this stage for complete vitrification. Finally, for the cooling stage, the temperature must be slow and steady. A clamp may take two weeks to cool.