It is a long cry from the primitive method of mixing and molding
brick by hand and drying them in the sun, to the modern technical
methods and power machinery used by the American manufacturer.
Determined by the kind of material, whether surface clay, fire
clay or shale, and the kind of brick wanted, there are three chief
methods of manufacture, slop-mold, wire-cut, and dry-press.
By the first method, the clay, in a soft condition, is pressed by
the machine into molds which have been flushed with water--hence
the term slop-mold--or sprinkled with sand, in which case the brick
are called sand-mold. By the second method, the clay or shale is
ground and tempered into the consistency of a stiff mud which is
forced by an auger machine through a die, in the form of a stiff
mud ribbon, having the cross section of a brick. This stiff mud
ribbon is carried by a belt to a steel table under a series of
piano wires strung on a frame which is revolved by the machine at
proper intervals, cutting the clay ribbon into the desired sizes.
These stiff mud machines will turn out as many as 100,000 face
brick a day, and in some common brick plants they are built for
a 250,000 to 300,000 daily output. The dry-press method reduces
the clay to a fine granular form which is then, in nearly a dry
condition, forced under immense pressure into the proper sized
molds.
The brick as they come from the machines are known as "green" and
require, except in the case of the best dry-press brick, a certain
period of drying before being set in the kilns where, for from five
to ten days, depending on the quality of the ware and the general
conditions, they are subjected to a process of burning before they
are ready to be built into the wall.