FULL information with regard to the materials used in the construction of buildings is given in Part III. of this work. This chapter will contain only so much as is necessary to meet the requirements of the Second Stage or Advanced Course.
Ordinary building bricks are made of clay or other earths subjected to various processes, such as clearing from stones, grinding if necessary, and mixing in some cases with chalk. These vary somewhat according to local practice, influenced by the nature of the material. The clay is formed, after mixing with water to a plastic condition, to the required shape by hand in moulds, or by machines, dried, and then burnt either in kilns (large ovens) or clamps (piles of the dried bricks themselves).
Machine-made Bricks are generally denser and heavier than those made by hand. In some machines the bricks are cut off by a wire: they then have no frog; in others the clay is pressed when nearly dry in a mould, and these generally have a frog, and are often pierced through with holes to make them lighter.
This differs in various localities, but in some brickfields near London there are three general classes: -
Malms, in which the clay is mixed with about 1/16 chalk, and cinders.
Washed, in which less chalk is added to the clay.
Common, in which no chalk is added.
These classes are divided into several varieties, the principal of which are - Cutters or Rubbers of even texture and very soft, so that they can be cut and rubbed to accurate shapes and to a smooth face.
Facing Paviors, hard-burnt malm bricks of good shape and colour, used for facing superior work.
Hard Paviors are more burnt, slightly blemished, and used for copings, superior facing, etc.
Stocks, good hard bricks, used generally for ordinary good work.
Grizzles and Place Bricks, which are weak, under-burnt, inferior bricks..
Chuffs are bricks on which the rain has fallen when they were hot, making them full of cracks and useless.
Burrs are lumps of over-burnt bricks vitrified and run together.
Machine-made Bricks may be classed as Pressed or Wire-cut, of each of which there are several varieties.
They should be well burnt, hard, ringing well when struck together, free from cracks and lumps, especially lumps of lime, regular in shape and uniform in size, not absorbing more than 1/6 of their weight of water.
This varies; but near London ordinary bricks are about 8¾ inches long, 4¼ inches broad, and 2½ inches thick, and weigh about 7 lbs each.