Page:EB1911 - Volume 04.djvu/541

 Mixtures of sand, lime and cement (and of certain ground blast-furnace slags and lime) were introduced; the moulding was done under hydraulic presses and the bricks afterwards treated with carbon dioxide under pressure, with or without the application of mild heat. Some of these mixtures and methods are still in use, but a new type of mortar brick has come into use during recent years which has practically superseded the old mortar brick.

Sand-lime Bricks.—In the early ’eighties of the 19th century, Dr Michaelis of Berlin patented a new process for hardening blocks made of a mixture of sand and lime by treating them with high-pressure steam for a few hours, and the so-called sand-lime bricks are now made on a very extensive scale in many countries. There are many differences of detail in the manufacture, but the general method is in all cases the same. Dry sand is intimately mixed with about one-tenth of its weight of powdered slaked lime, the mixture is then slightly moistened with water and afterwards moulded into bricks under powerful presses, capable of exerting a pressure of about 60 tons per sq. in. After removal from the press the bricks are immediately placed in huge steel cylinders usually 60 to 80 ft. long and about 7 ft. in diameter, and are there subjected to the action of high-pressure steam (120 ℔ to 150 ℔ per sq. in.) for from ten to fifteen hours. The proportion of slaked lime to sand varies according to the nature of the lime and the purity and character of the sand, one of lime to ten of sand being a fair average. The following is an analysis of a typical German sand-lime brick: silica (SiO2), 84%; lime (CaO), 7%; alumina and oxide of iron, 2%; water, magnesia and alkalis, 7%. Under the action of the high-pressure steam the lime attacks the particles of sand, and a chemical compound of water, lime and silica is produced which forms a strong bond between the larger particles of sand. This bond of hydrated calcium silicate is evidently different from, and of better type than, the filling of calcium carbonate produced in the mortar-brick, and the sand-lime brick is consequently much stronger than the ordinary mortar-brick, however the latter may be made. The sand-lime brick is simple in manufacture, and with reasonable care is of constant quality. It is usually of a light-grey colour, but may be stained by the addition of suitable colouring oxides or pigments unaffected by lime and the conditions of manufacture.

Strength of Brick.—The following figures indicate the crushing load for bricks of various types in tons per sq. in.:—

See also.

 BRICKFIELDER, a term used in Australia for a hot scorching wind blowing from the interior, where the sandy wastes, bare of vegetation in summer, are intensely heated by the sun. This hot wind blows strongly, often for several days at a time, defying all attempts to keep the dust down, and parching all vegetation. It is in one sense a healthy wind, as, being exceedingly dry and hot, it destroys many injurious germs of disease. The northern brickfielder is almost invariably followed by a strong “southerly buster,” cloudy and cool from the ocean. The two winds are due to the same cause, viz. a cyclonic system over the Australian Bight. These systems frequently extend inland as a narrow V-shaped depression (the apex northward), bringing the winds from the north on their eastern sides and from the south on their western. Hence as the narrow system passes eastward the wind suddenly changes from north to south, and the thermometer has been known to fall fifteen degrees in twenty minutes.

 BRICKWORK, in building, the term applied to constructions made of bricks. The tools and implements employed by the bricklayer are:—the trowel for spreading the mortar; the plumb-rule to keep the work perpendicular, or in the case of an inclined or battering wall, to a regular batter, for the plumb-rule may be made to suit any required inclination; the spirit-level to keep the work horizontal, often used in conjunction with a straight-edge in order to test a greater length; and the gauge-rod with the brick-courses marked on it. The quoins or angles are first built up with the aid of the gauge-rod, and the intermediate work is kept regular by means of the line and line pins fixed in the joints. The raker, jointer, pointing rule and Frenchman are used in pointing joints, the pointing staff being held on a small board called the hawk. For roughly cutting bricks the large trowel is used; for neater work such as facings, the bolster and club-hammer; the cold chisel is for general cutting away, and for chases and holes. When bricks require to be cut, the work is set out with the square, bevel and compasses. If the brick to be shaped is a hard one it is placed on a V-shaped cutting block, an incision made where desired with the tin saw, and after the bolster and club-hammer have removed the portion of the brick, the scutch, really a small axe, is used to hack off the rough parts. For cutting soft bricks, such as rubbers and malms, a frame saw with a blade of soft iron wire is used, and the face is brought to a true surface on the rubbing stone, a slab of Yorkshire stone.

In ordinary practice a scaffold is carried up with the walls and made to rest on them. Having built up as high as he can reach from the ground, the scaffolder erects a scaffold with standards, ledgers and putlogs to carry the scaffold boards (see ). Bricks are carried to the scaffold on a hod which holds twenty bricks, or they may be hoisted in baskets or boxes by means of a pulley and fall, or may be raised in larger numbers by a crane. The mortar is taken up in a hod or hoisted in pails and deposited on ledged boards about 3 ft. square, placed on the scaffold at convenient distances apart along the line of work. The bricks are piled on the scaffold between the mortar boards, leaving a clear way against the wall for the bricklayers to move along. The workman, beginning at the extreme left of his section, or at a quoin, advances to the right, carefully keeping to his line and frequently testing his work with the plumb-rule, spirit-level and straight-edge, until he reaches another angle, or the end of his section. The pointing is sometimes finished off as the work proceeds, but in other cases the joints are left open until the completion, when the work is pointed down, perhaps in a different mortar. When the wall has reached a height from the scaffold beyond which the workman cannot conveniently reach, the scaffolding is raised and the work continued in this manner from the new level.

. 1.It is most important that the brickwork be kept perfectly plumb, and that every course be perfectly horizontal or level, both longitudinally and transversely. Strictest attention should be paid to the levelling of the lowest course of footings of a wall, for any irregularity will necessitate the inequality being made up with mortar in the courses above, thus inducing a liability for the wall to settle unequally, and so perpetuate the infirmity. To save the trouble of keeping the plumb-rule and level constantly in his hands and yet ensure correct work, the bricklayer, on clearing the footings of a wall, builds up six or eight courses of bricks at the external angles (see fig. 1), which he carefully plumbs and levels across. These form a gauge for the intervening work, a line being tightly strained between and fixed with steel pins to each angle at a level with the top of the next course to be laid, and with this he makes his work range. If, however, the length between the quoins be great, the line will of course sag, and it must, therefore, be carefully supported at intervals to the proper level. Care must be taken to keep the “perpends,” or vertical joints, one immediately over the other. Having been carried up three or four courses to a level with the guidance of the line which is raised course by course, the work should be proved with the level and plumb-rule, particularly with the latter at the quoins and reveals, as well as over the face. A smart tap with the end of the handle of the trowel will suffice to make a brick yield what little it may be out of truth, while the work is green, and not injure it. The work of an efficient craftsman, however, will need but little adjustment.

For every wall of more than one brick (9 in) thick, two men should be employed at the same time, one on the outside and the 