Q&A / 

Bricks and Colored Mortar

Why So Strong?

Bricks are basically a form of artificial rock or stone. They do not occur naturally. The raw material from which they are made, however is a raw material which is very abundant. Clay, which is a major portion of many soils, is used to manufacture brick. Shale, a soft sedimentary rock, is used as well. These two materials are found just about everywhere in the world.

The process of turning clay and shale into bricks is a somewhat simple process. The clay and/or shale is refined and then mixed with a small amount of water until it can be shaped into bricks. The bricks are then dried and put into a kiln, sometimes for days. The kiln is nothing more than a very hot oven. Temperatures can reach in excess of 2,000 degrees F. This heating or firing process is what transforms the soft clay into hard bricks. In this manner, the clay and shale become an artificial stone.

Surface Textures

Prior to placing the soft bricks into the kiln, manufacturers can do any number of things to the soft bricks to give them a texture. Some bricks are either rolled, brushed, scratched, or dimpled after they come out of the forming die.

Some manufacturers offer the capability to produce custom textures for a certain brick, however it is very expensive to have this done. But, if you have the money and want a very unusual texture, it can be produced. Patterns, letters, even sculptures can be produced on the face of individual bricks.

Coatings

If you visit a brick showroom, you will undoubtedly come across bricks which have coatings applied to them. These coatings, once again, are applied prior to the bricks entering the kilns.

Some of the coatings commonly seen are sand coatings, colored slurries of fine clay, pigments and water called "engobes", and Portland cement mixed with pigments. The colored Portland cement is mixed with water and applied to the bricks.

All of the coatings are semi-permanent. They do not produce color throughout the body of the brick. If the coating wears off or is chipped, you will see the inside color of the brick. Thus, it is important for you to choose a brick with a high quality coating if you like the appearance of these products. This is especially true of the Portland cement-based slurries. I have seen these coatings wash off of bricks after 15 or 20 years. This can be a severe problem if all the bricks on your house do not receive the same amount of weathering.

Strength

Not all bricks have the same strength. Their strength is a function of the type of clay and/or shale used as a raw material, and the temperature and length of time the bricks spend in the firing kiln. The higher the temperature and the longer you leave a brick in the kiln, generally speaking, the stronger it will be at the end of the process.

This is very important to know when shopping for bricks, as the last two points are directly related to the cost of a brick. Think of it, if you use more fuel to achieve a higher kiln temperature and you leave the bricks in for a longer period of time, your costs per brick are going to be higher.

Bricks which have been fired longer and hotter generally are a deeper color. Deep red, purple, and brown bricks are usually very hard.

A good example of bricks which are not hard and durable are those orange colored bricks you often see from old buildings in our inner cities. These bricks were usually produced in lower temperature crude kilns.

The hardest portion of some bricks is just the outer 1/4 inch. This is why it is dangerous to sandblast bricks. Sandblasting can expose the soft inner portion of the brick and cause it to weather at an accelerated rate.

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