When the raw bricks are half dry they are scintled, that is, placed diagonally and a little distance apart, so that the wind may pass between them. They therefore take up more room in plan, but as the bricks are drier, about fourteen courses may be piled up instead of eight as before.
The bricks on the hacks are generally protected from the weather by light coverings or roofs, made of straw, called lews, or by boards or tiles.
In permanent brickyards the hacks are sometimes covered by sheds, with sliding roofs so that they may be uncovered in favourable weather and closed in case of rain, or when the sun is so strong as to warp the bricks.
The time of drying varies according to the weather. The raw bricks generally take about ten days before being scintled, and about three to six weeks for the whole process of drying.
Machine-Moulding, - When there is a large number of bricks to be made at the same spot, it pays to set up machines for moulding, and in cases where the clay is very hard, stony, or in any way refractory, machines become a necessity.
There are several varieties of machines for brick-moulding, but they may be divided into two general classes. These will be just referred to, but to describe even the most common brickmaking machines in detail would be beyond the province of these Notes.
In these the clay is first pugged in the machine, next forced through an opening of about 10 inches by 5 inches in a plastic band, from which the bricks are cut off by means of wires, and then dried or burnt as usual.
Dry Clay Machines in which the clay is first reduced to powder, then filled by the machine dry into a mould, and subjected to enormous pressure which consolidates it, and forms a well-shaped brick with hard even surfaces.
These machines are well adapted for stony and marly clays, and they are economical inasmuch as they save the expense and time employed in drying, which process is, of course, unnecessary.
Some machines receive the clay in a semi-dry condition, and deal with it in the same way as the dry clay machines just mentioned.
This may be done in hand presses, or in larger machines worked by steam power.
Such treatment gives the bricks good faces and arrises, but they require more care in drying and burning, and the oil necessarily used, gives them a glazed surface, which peels off upon exposure to the weather.
Dressed Bricks after being moulded are beaten with a dresser shaped like a small cricket bat, and sometimes tipped with iron. This toughens the clay, corrects its warping, and improves the arrise3 of the brick.
"Polished Brides, as they are called, are rubbed upon a bench plated with iron, to make their surfaces perfectly even, and are also dressed with a dresser as before described.
"This process is only gone through with the very best bricks, and its cost is such that it is not employed to any very great extent."1
Most hand-made bricks have a hollow on one of the larger surfaces called the "frog" or "kick."
The object of this is to afford a key for the mortar. The reason why there is not a hollow on both sides in hand-moulded bricks is that the top of the brick is struck off to a flush surface by the moulder.
Bricks should be laid with the hollow uppermost.2
Wire-cut bricks (see above) have, of course, no frogs.
In some machine bricks made by pressure there is a frog on each side.