This section is from the book "Spons' Mechanics' Own Book: A Manual For Handicraftsmen And Amateurs", by Edward Spon. Also available from Amazon: Spons' Mechanics' Own Book.
The art of making and burning bricks does not come within the range of the artisan who employs them, and need not be described here. Bricks may bo divided into 3 classes : .
(1) "Cutters" or; "rubbers," i. e. bricks intended to bo cut or rubbed to some shape different from that in which they were originally moulded.
(2) Ordinary bricks, intended to be used without cutting except where required to form the bond; the best of these are selected for fronts, and are termed facing bricks; specially hard varieties are used for coping, also for paving, quoins, and other positions where they will be subjected to unusual wear.
(3) Under-burnt and misshapen bricks, only fit for inside work. Of each of these classes there are in most brickfields several varieties, varying in quality according to circumstances. Their general characteristics are as follow.
Cutters or rubbers are purposely made sufficiently soft to be cut approximately to the shape required with a trowel, and then rubbed to a smooth face and to an accurate shape. To ensure this, they are made of washed earth carefully freed from lumps of all kinds, and uniform in composition throughout its mass. The best rubbers are burnt to a point little short of vitrification. Inferior kinds are often stinted in firing; the cohesion between the particles is small, and they are easily destroyed by rain or frost. For the sake of durability, it is better to avoid rubbers in all exposed work, and to use " purpose-made" bricks moulded to the shape required and thoroughly well burnt. This is often done in good work.
Ordinary building bricks include the bulk of those required for building. The qualities and characteristics of these vary, not only in different localities, but also in the same brickyard. Such bricks are made either from washed earth or malm, from partly washed earth, or from earth which has merely been tempered, not washed at all. They should be hard and well shaped, those most uniform in colour being selected for facing, and the whole of the remainder being fit to use for good sound work.
Under-burnt bricks are generally known as "grizzle" or "place" bricks, in some places as "samel" bricks. They are always soft inside, and sometimes outside also, are very liable to decay, and unfit for good work. They are, however, often used for the inside of walls.
The names given to different classes of bricks vary in different districts, and even in different brickfields of the same district. The subjoined list of names for clamp-burnt bricks may be taken as a specimen, with the relative prices per 1000. The bricks are divided generally into 3 classes - "malms," "washed," and "common" - according to the manner in which the earth for them is prepared. For the third or common class the earth is not washed at all. All 3 classes are moulded and burned in exactly the same manner, and are then further sorted into a number of varieties according to the manner in which they have been affected by the fire.
The classes are subdivided as follows: - (Malms) cutters, 110s.; best seconds, 85s.; mean ditto, 75s.; pale ditto, 45s.; brown facing paviors, 55s.; hard paviors, 50s.; shippers, 37s. 6d., 48s.; bright stocks, 50s.; grizzle, 3Ss.; place, 35s. ( Washed) bright fronts, 60s.; stocks, 45s.; shippers, 48s.; hard stocks, 42s.; grizzles, 36s.; place, 34s. (Common) shippers, 48s.; stocks, 44s.; grizzles, 36s.; rough stocks, 35s.; place, 33s.
Cutters have already been described. Seconds are similar to cutters, but with some slight unevenness of colour. Facing paviors are hard-burned malm bricks of good shape and colour used for facing superior walls. Bright fronts are the corresponding quality from "washed" earth. Hard paviors are rather more burned, and slightly blemished in colour; used for superior paving, coping, etc. Shippers are sound, hard-burned bricks, not quite perfect in form; chiefly exported, ships taking them as ballast. Stocks are hard-burned bricks, fairly sound, but more blemished than shippers; used for the principal mass of ordinary good work. Hard stocks are over-burnt bricks, sound, but considerably blemished both in form and colour; used for ordinary pavings, for footings, and in the body of thick walls. Grizzle and place bricks are under-burnt, very weak, and 2 out of 5 " common " or unwashed place bricks are allowed to be bats, the stones left in the unwashed earth making them very liable to breakage. These two last-mentioned descriptions are only used for inferior or temporary work, and are commonly covered with cement rendering to protect them from the weather when intended to be permanent.
Chuffs are bricks upon which rain has fallen while they were hot, making them full of cracks, and perfectly useless. Burrs are lumps of bricks vitrified and run together; used for rough walling, artificial rock-work, etc. Bats are broken bricks. Of these varieties, those from "common" or unwashed clay are hardly ever quite perfect in form, on account of the stones left in the earth, which make them shrink unequally, and become distorted in burning. Bricks from " washed " clay suffer in the same way to a less degree.
Kiln-burnt bricks are generally pretty equally burnt, and are classed chiefly according to the process by which they are made.
Bricks used in ordinary buildings generally are, or should be, the best that are made in the neighbourhood. Some descriptions of bricks, however, are universally known, and are used even outside the locality in which they are made, either for special purposes, or in buildings of such importance as to justify incurring the expense of carriage.
Good building brick should be sound, free from cracks and flaws, also from stones, or lumps of any kind. Lumps of lime, however small, are specially dangerous; they slake when the brick is exposed to moisture, and split it to pieces. A small proportion of lime finely divided and disseminated throughout the mass is an advantage, as it affords the flux necessary for the proper vitrification of the brick. In examining a brick, lumps of any kind should be regarded with suspicion, and tested. In order to ensure good brickwork, the bricks must be regular in shape and uniform in size. Their arrises (edges) should be square, straight, and sharply defined. Their surfaces should be even, not hollow; not too smooth, or the mortar will not adhere to them. The proportion of water that a brick will absorb is a very good indication of its quality. Insufficiently burnt bricks absorb a large proportion, and are sure to decay in a short time. It is generally stated in books that a good brick should not absorb more than 1/15 of its weight of water.
The absorption of average bricks is, however, generally about 1/6 of their weight, and it is only very highly vitrified bricks that take up so little as 1/13 or 1/15.
Good bricks should be hard, and burnt so thoroughly that there is incipient vitrification all through. This may be seen by examining a fractured surface, or the surface may be tested with a knife, which will make hardly any impression upon it unless the brick is under-burnt. A brick thoroughly burnt and sound will give out a ringing note when struck against another. A dull noise indicates a soft or shaky brick. A well-burnt brick will be very hard, and possess great power of resistance to compression. A really first-class rubber will not be easily scored by a knife even in the centre, and the finger will make no impression upon it. Such a brick will be of uniform texture, compact, regular in colour and size, free from flaws of any description. It is easy to distinguish clamp-burnt, kiln-burnt, and machine-made bricks. In clamp-burnt bricks, the traces of the breeze mixed with the clay can generally be seen. Kiln-burnt bricks very often have light and dark stripes upon their sides, caused by their being arranged while burning with intervals between them. Where the brick is exposed, it is burnt to a light colour; where it rests upon or against other bricks, it is dark. In some cases care is taken to prevent this, and the best kiln-burnt bricks are of uniform colour.
Machine made bricks may generally easily be distinguished, if wire-cut, by the marks of the res; if moulded, by the peculiar form of the mould, letters on the surface, etc, or sometimes by having a frog on both sides. In many cases the marks made by pronged rks, used for packing the bricks, may be seen on their sides.
Before 1839 a duty was paid upon bricks; their size was then practically fixed by ct of Parliament, and it has since remained materially unaltered. Ordinary bricks in e neighbourhood of London are about 8 3/4 in. long, 4 3/4 in. wide, and 2 1/2 in. thick, and eigh about 7 lb. each. In different parts of the country, the size and weight vary ghtly; in the north of England and in Scotland they are larger and heavier. A very rge brick is inconvenient for an ordinary man to grasp, and a heavy brick fatigues the icklayer, who has to lift it when wet and lay it with one hand. In order to obtain od brickwork, it is important that the length of each brick should just exceed twice breadth by the thickness of a mortar joint.
The best method of testing bricks is to see if they ring when struck together; to certain the hardness by throwing them on to the ground, or by striking them against ler bricks. The fractured surface should also be examined in order to ascertain if it hibits the characteristics mentioned. Brard's test is sometimes used for bricks, but is t of much practical benefit. The amount of water absorbed by bricks is to a certain tent an indication of their quality, and their resistance to compression, either singly or len built into brickwork, will show whether they are strong enough for the purpose paired.