Combination of ilalerials.—Various combinations of materials are extensively used in building operations, to some of which more particular reference will be made hereafter. General suggestions bearing on this sub ject embrace a statement that, while two kinds of materials sometimes have the effect of improving or strengthening a wall, in other cases they produce the opposite result. It is said that a stone-rubble wall is improved by bonding courses of brickwork at short intervals, and that a brick wall is improved by thorough courses at intervals of g-ood stone properly ad justed, but that elements of weakness rather than additional strength are introduced when a stone-rubble wall is faced with brickwork or when a brick wall is faced with wrought stone.
Scafoldings.—Tlie bricklayer's scaffold is usually carried up with the wall and made to rest upon it. The scaffold consists of standards, ledgers or runners, putlogs—sometinies called " putlocks "—sheeting or scaffold boards, and braces. The standards are poles, which are placed from TO TO 12 feet apart in a row about 4Y2 feet from the wall and parallel with it. These standards, which are firmly fixed in the ground or planted in tubs of earth or mortar, are from 2o to 5o feet long, and can be extended by splicing. The ledgers or runners, which are poles secured to the standards by ropes, lie horizontally, parallel with the wall at the level of the highest course of bricks laid. The putlog-s or putlocks are cross-pieces, generally of sawn birch, about 6 feet long and placed from 4 to 6 feet apart. They are fixed at one end in the wall, on the middle of a stretcher occupying the place of a header, which is to be afterward inserted. The other end of the putlogs, which make the platform upon which the bricklayer stands, rests on the ledger.
The sheeting or scaffold boards form the gangway, and the braces are Toles lashed diagonally across and outside the standards for further secur ity when the scaffolding is run to a great height. The mortar is usually placed on boards about 3 feet square along the putlogs, with bricks, to suit the convenience of the bricklayer. As the work is continued another ledger is rigged lip above at a distance of about 3Y2 feet, that the bricklayer may insure good work by never laying his bricks at too great a height.
The supply of brick and mortar is furnished constantly from below, with due care that the ledgers are never overloaded, so as to rest too heavily upon the newly-laid courses. Rubble walls can be erected from the scaf foldings just described, but in better styles of masonry and in large build ings the scaffolds are built double, a second row of standards being so fixed as to carry the inner ends of the putlog,s and avoid any injury to the wall, while securing a firm platform for the workmen.
The suspended scaffold is a convenient arrangement for painting or pointing a house-front without obstructing the sidewalk. A platform of planks makes a sufficient space for the workmen, who can lower or raise it at will by ropes and pulleys made fast to beams projecting from the upper windows or secured to the roof-timbers. Various new devices are intro duced in American cities from time to time which presumably represent improvements on old methods of scaffolding aud of furnishing brick and mortar to bricklayers.
Precautions against aggregation of population in cities, the immense increase in manufactures, the introduction of gas and steam, the discovery and extended use of petrolemn, and the vast extent and altitude of building structures, are all tending so to multiply the sources of conflagra tion that precautions against fire are becoming of vital importance to the community. The employment of incombustible materials in architecture
would seem to afford one of the best of preventive methods. The modes of building in many countries of continental Europe secure great safety in this respect. This immunity is obtained by the -use of massive walls with incombustible fillin?-, between joists and rafters, roofs of terra-cotta tiling, brick or stone partition walls, and floors and stairways of tile or marble. Timber impregnated with a solution of copperas is regarded as a fire-resist ant, and shingles, window-frames, and cornices could be well protected after being placed in position by coating, with solutions of such fireproof salts as alum, copperas, and borax, and also with paints containing the same materials. This precaution would be most serviceable in the coun try, where isolated dwellings are frequently of wood and are much endan gered by fire.
Concrete as a building material has been well tested as a fireproof com position, and ordinary plaster, if of sufficient thickness, has shown great resisting quality. Brick walls built so as to allow proper settling and bed ded in mortar containing Portland cement furnish a most valuable obstacle to flame. Mortar of good quality has in itself, when aided by brick, a sup porting- quality which gives a certain elasticity to the wall and breaks the heat-conduction of the brick, its granular formation yielding to torsion and strain without breaking. Hollow bricks have a greater relative strength, lightness, and elasticity, but the air in the interior spaces may expand dan gerously in case of fire, if means of escape are not provided. In a thick wall the interior bricks should be entirely encased in mortar, adding much to the supporting and resisting power. Stone walls of irreg,rular and rather small pieces have less ability to resist fire than brick walls; but when they are of ample thickness and are well laid in sufficient mortar, they may be estimated at the strength of brick walls of half the same thickness. Large stones, although necessarily built with less mortar, have by their great weight a resistance to vibration under fire.
Lofty buildings have an increased danger from fire, on account not only of the tendency of flame to ascend, but also of the disintegration arising from the tremor or vibration in high walls, particularly when subjected to the incidental movements of machinery, etc. When brick walls are not of excessive height, they regain elasticity after cooling-, and are often used in re-building after conflagration. In order to erect a fire-proof building it has been proposed to employ concrete for floors, washboards, ceiling-s, cor nices, sides, lintels, casings, and mouldings of doors and windows. The partitions would be brick, and the stairs either of terra-cotta, concrete, or stone slabs resting upon brick arches. An incombustible filling would be placed between wooden joists, with a concrete ceiling supporteci by a net ting of wire. The roof with its stipports would be constructed like the floors, and covered on the outside with copper, concrete, or thick galvan ized sheet iron. Brick piers for supporters, upon heavy brick arches, would complete the edifice.