These contain a certain proportion of malm, and are made in two ways.
In some parts of the country - in Essex for example - they are composed wholly of an inferior malm, made like the malm described above, except that the proportion of chalk is only one half of that in the ordinary malm, and the cinders are unscreened.
In other brickfields, including those near London, a certain proportion of ordinary liquid malm is poured over unwashed clay, and mixed with it so that the whole becomes an inferior maimed clay.
The quantity required for 1000 bricks of ordinary size ranges from 13/4 to 31/2 cubic yards, measured before digging. The stronger the clay, the more of it is required.
The moulds used are rectangular boxes without top or bottom, about 10 inches long, 5 inches wide, and 3 inches deep, the exact size depending upon that of the brick required, and upon the contraction of the clay in burning, which may be about 1/10 or 1/12 of the linear dimensions.
The mould stands either upon the table at which the moulder works - in which case the bottom of the brick is flat - or it rests upon a stock board, or bottom made to fit the mould, and upon which is a raised projection which forms an indentation or frog l in the bottom of the brick.
The process of hand-moulding consists in dashing a clot of clay into the mould, and pressing it home so as thoroughly to fill every corner.
When a stock board is used the lower side of the brick rests upon it. The superfluous clay protruding above the top is swept or scraped off by a strike or straight-edge of wood or steel.
When there is no stock board the bottom of the brick rests upon the moulding-table, and the top surface is formed by means of a plane, which is a piece of board about 9 inches by 3 inches with a short vertical handle near one end.
Slop-moulding is the term used when the mould is dipped frequently in water to prevent the wet bricks from sticking to it.
1. It may be carried by a boy in the mould to the drying floor or ground, and there deposited, the mould being taken off and returned to the moulder. Or,
2. It may be deposited upon a pallet (a piece of board -| inch thick, the same width as the mould but longer), and placed by the boy upon a bearing-off or hack barrow for removal to the drying ground. These barrows are made with springs, and run upon smooth wrought-iron wheeling plates, so as to shake the brick as little as possible.
The raw moulded bricks may be dried either in sheds under cover or out of doors.
Drying sheds are extensively used in Nottinghamshire and the Midland counties, and they insure the great advantage of being independent of weather in drying the bricks.
1 Sometimes called a kick.
Where coals are cheap the sheds may be warmed by flues running under the floor. This secures the raw bricks against the effects of frost, and enables the brickmaking to be continued throughout the winter.
Hacking. - Bricks to be dried out of doors are placed upon hacks, which are long parallel banks raised about 6 inches from the ground. They have a slight inclination toward the kiln to facilitate drainage and transport of the bricks, and are sometimes made of brick rubbish and ashes so that they may be quite dry.
The bricks are placed upon the hacks, sometimes laid square in plan, sometimes diagonally, and piled up. They should not be more than eight courses deep, or the lowest course would be liable to be crushed.