Rick Portiera, age 9, of Mt. Prospect, I11., for his question:
HOW ARE BRICKS MADE?
The oldest manufactured building material is the brick. Sun dried brick, similar to adobe brick, was used before 4000 B.C. by the ancient residents of Egypt, Assyria and Babylonia. The Israelites, during their captivity in Egypt, were involved primarily in brickmaking. They made sun dried bricks from clay that was taken from the Nile River.
A brick is a construction material that has been hardened into the shape of a block. Most bricks are made from clay or shale, although some are made of concrete.
After clay for bricks has been dug, it is crushed and ground thoroughly in a rotating pan with heavy rollers. This machine is called a dry pan.
Next the clay is screened to remove coarse material. Water is then added as revolving knives chop and mix the clay into a plastic mass.
Clay bricks are then molded into shape by either the stiff mud, soft mud or dry press process. The important difference in the three methods is the amount of water used.
The stiff mud process is used to make most building bricks. After water is added, the brickmaking machine forces the clay through an opening to form a long ribbon. The ribbon of clay is cut into brick sizes by a brick cutter, a piece of equipment that has evenly spaced wires which are used to slice through the stiff clay.
In the soft mud process, a handmade brick is produced. Molds are dipped into sand or water to prevent the clay from sticking. The soft paste is then pressed into the molds.
An almost perfect face brick is brought about with the dry press process. Only enough water is added to the clay to make it damp. The clay is then pressed into molds.
Sometimes air is removed from the clay by attaching a vacuum pump to the brickmaking machine. Removing air makes the clay stronger and easier to handle.
After bricks are formed, they are stacked in drying rooms where air is heated to temperatures from 100 to 300 degrees Fahrenheit. The heated air removes much of the water. The process is handled slowly so the bricks do not crack or shrink.l
Finally the bricks are burned or fired in a kiln that has a temperature between 1600 and 2000 degrees Fahrenheit. In this heat, clay particles become partly melted and fuse together, forming a brick that is strong and hard.
Clays that are high in iron compounds make red bricks. Clays with low iron content are used for yellow or cream colored bricks.
Clay and shale bricks of various colors are made for use as face bricks. These are used on exposed surfaces of buildings.