Page:Encyclopædia Britannica, Ninth Edition, v. 4.djvu/505

Rh BRICKWORK.] erected for the purpose G or 8 feet above the work ; but this process has been very justly censured as uncertain by eminent engineers, who prefer to put it in layers of not more than one foot in thickness, and to level each course, ramming it down thoroughly. When the lime is too hastily put into the trenches, and has not had time to be thoroughly slaked, the process will continue, and the mass will puff or swell and sometimes cause considerable mischief. Wing walls of bridges have been thrust out by this means. To make a solid concrete all the interstices of the gravel should be filled with the sand, and the lime and the water will be absorbed without any increase of bulk. In France the lime is first made into a paste, and the mixture is then called bcton, not concrete ; this is a more scientific process for obtaining a sound substance. In some experiments made by the Architectural Publication Society, where the materials were carefully mixed, no change took place in the bulk ; but some experimentalists, practical men, and writers differ on this point, and assert there is a loss of one-seventh in bulk when set. The lime, if it can be procured, should be hydraulic ; and concrete is much improved by the addition of the volcanic sands. French authors recommend, as good proportions, one-fifth hydraulic lime, one-fourth pozzuolana, one-eighth sharp sand, and the rest broken stone or gravel ; or 20 per cent, hydraulic lime, the same of trass, the same of sharp sand, 15 per cent, of gravel, and 25 per cent, of broken stone. Perhaps the very best concrete is made of a simple mixture of gravel, sand, and Portland cement. It is unnecessary to enter into the details of foundations in water, as this but seldom comes within the ordinary builder s province. Digger or Excavator. The digger works with a pick-axe and a spade or shovel. With the pick-axe he breaks down the soil if it be hard or very stiff, and throws it out with the shovel ; but compacted sand and alluvial soil are spitted and thrown out with the spade alone, without previous breaking down. When rock occurs in a foundation, the assistance of the quarryman is requisite to cut through or blast it, as the occasion may require. The digger should be required to produce a perfect level in every direction, and especially in trenches for walls; nor may this be done by replacing loose matter, but the level must be produced on the solid or undisturbed bed. A good excavator will dig and throw out, of common soil, into a basket or wheelbarrow, 8 or 10 yards per diem ; but of stiff clay or firm gravel not more than G yards. When the excavation has to be dug to a depth about the height of a man it will be necessary to strut the ground to prevent its falling in, especially if it be of a sandy, loose, or watery nature. This is done by placing on each side of the cutting upright planks against the soil, which may be either open or close, according to the quality of the soil, and against these one or more horizontal waling pieces secured by horizontal cross pieces or struts, and wedging up as necessary. On these struts are formed the landings or stages on which the lowest workman throws the soil he digs up, which is then again thrown up by a second man to another stage or to the surface, according to the depth. Sometimes the soil is hoisted in baskets or tubs raised by a windlass worked by hand, or by a horse-run. When the work has been executed for which the excavation was prepared, the digger has to fill in over and around it, carefully ramming the soil to prevent inequalities on the surface by the soil sinking, and to prevent water soakiiif in which might affect the foundations. BRICKWORK, The tools and implements employed by the bricklayer are the trowel, plumb-rule, rod, level, square, bevel, line-pins 457 and lines, raker, jointer, crow-bar, pick-axe, and rammer, , together with a hod and spade for his labourer. Besides these there are sundry others, as an axe, saw, and rubstone, used in ctutting and gauging bricks, and some which are peculiar to tiling and paving. A pug-mill and screens for mixing and tempering mortar, and tubs and pails for water, are alsoauxiliaries of great importance. In ordinary practice the bricklayer s scaffolds are carried Scaffolding, up with the walls, and are made to rest on them. Having built up the walls as high as he can reach from the ground, he plants a row of poles, which vary in height from 30 to 40 and even 50 feet, parallel to and at a distance of about 4 feet G inches from the walls, and from 10 to 12 feet apart. To these, which are called standards, are attached by means of cords other poles called ledgers, horizontally and on the inside, with their upper surface on a level with the highest course of the wall yet laid ; and on the ledgers and wall short transverse poles, called putlogs or putlocks, are laid as joists to carry the floor of scaffold boards. These putlocks are placed from 4 to G feet apart, according to the length and strength of the scaffold boards ; and the ends which rest on the walls are carefully laid on the middle of a stretcher, so as to occupy the place of a header brick, which is inserted when the scaffolds are struck after the work is finished. On the floor of the scaffold thus formed the bricklayer stands, and the materials are brought up ladders to him by labourers in hods from the ground below ; or they are hoisted up in baskets and buckets by means of a pulley-wheel and fall ; or by the horse-run, which is more generally used, formed of a level pathway in which the horse moves, drawing up the load by the intervention of snatch blocks and guide wheels ; or by the now usual hoisting- machine, worked by men, horses, or steam- power. The mortar is placed on ledged boards about 3 feet square, at convenient distances ; and the bricks are strewn on the scaffold between the mortar boards, leaving a clear way against the wall for the bricklayers to move along unobstructedly. The workman then recommences the operation of bricklaying, beginning at the extreme left of his course, and advancing to the right until he reaches the angle or quoin in that direction, or the place where his fellow-workman on the same side may have begun. Thus he goes on with course after course until the wall is as high as he can conveniently reach from that scaffold, when another ledger is tied to the poles, another row of putlocks laid, and the boards are removed up to the new level. The ledger and most of the putlocks, however, remain to give steadiness to the temporary structure, and so on to the full height of the wall, the poles being pieced out by additional lengths as may be required. If a scaffold be very much exposed, and run to a great height, it must be braced. This is done by tying poles diagonally across on the outside to the standards and ledgers, and it may be further secured by tying the ends of some of the putlocks to the ledgers ; but an outside scaffold should never be attached in any way to the building about which it stands. A scaffold should never be loaded heavily, as well on account of the work as of the scaffold itself; for the putlocks resting, as they do, on single bricks, in a green wall, they exert an injurious influence on it, which every additional pound weight on the scaffold must necessarily increase, and the putlocks themselves are liable to be bent or broken. A constant and steady supply of bricks and mortar on the part of the labourers, without overloading the scaffold at any one time, should be strictly required. The suspended scaffold is a very ingenious contrivance, Suspended by which pointing and other external repairs of a house can scaffold, be performed at a comparatively small cost, and without interference with the thoroughfare. The front can also be painted by the same means. Although known at least IV. 58.