BUILDING. 643 BUILDING. the same as in stone arches, the work of setting the arch-bricks beginning at the bottom en each side, and progressing unilornily upward until the two si<lcs meet at the crown of the arcli. FiKEi'ROOFiXG is the process of laying up or applying tireproof materials to Iwams, columns, etc. (See FiRKi'BOOF Construction.) The more common fireproof materials are burned-clay prod- ucts, plaster mixtures, and concrete. Burned-clay fireprooting and fireprooling of plaster mi.xtures are usually furnished by the manufacturers in molded blocks ready for erection : concrete fire- proofing is manufactured on the building-site, and is applied to the member to be protected in a plastic condition and afterwards hardens in place. Floor-construction and cohinm-proteetiou and partitions are the principal classes of fire- proofing work. Tile, terra-cotta, and plastic com- position blocks for fireproof floors are so made that when laid together they span the space be- tween floor-beams and imbed the beams them- selves. Floor-arches are built on centres, as are brick and masoniy arches, and by practically the same mode of procedure. To illustrate, a terra- cotta floor-areh is made up of two skewback blocks, which come next to the beams and are mokk'd so as to fit and enfold them, of a centre block or keyblock, and of several intermediate or haunch blocks. To erect such an arch the mason first suspends a centre of timber between the floor-beams. On this he sets the skewback blocks with a mortar joint between them and the beams. The haunch-blocks are then set one after another, with mortar joints, working from both ends, and last the keyblock is set. Finally the tops of the blocks are covered with a layer of concrete. Concrete iloor-arehes are built by sus- pending a suitable centre, spreading the concrete in layers and packing it firmly in position where it hardens, after which the centre is removed. Terracotta and plastic composition blocks for column-protection are so molded as to fit the column and are laid up with mortar joints much as brickwork is laid. Concrete fireproofing is applied to columns by placing molds around the columns and packing the annular space with con- crete which hardens in position. Partition-blocks are laid up with mortar joints exactly like ash- lar stonework. Lathing and Plastering are the processes of finishing walls and ceilings with lath and plaster. The very general practice of plastering walls and ceilings dates back only about a century; pre- vious to that time walls and ceilings were either wainscoted, boarded, or covered with canvas or tapestries, or else left unfinished. Brick walls and hollow tile, plastic composition and concrete ceilings and partitions have an affinity for plas- ter, and it may be applied directly to them : all other constructions require some form of lathing to serve as a ground to receive and hold the plaster. Practically, all dwellings of moderate cost, and a large proportion of other buildings, are lathed with wooden lath. Wooden lath is furnished the luiilder in strips about one-quarter of an inch thick and 1% inches wide and 4 feet long. Lathing is the process of nailing these strips parallel to each other, with one-quarter of an inch space Iietween them to the ceiling or jiarti- tion studding. Tn recent years the tendency toward fireproof construction has led builders and manufacturers to devise various stvlcs of metal lathing. Coarse-mesh wire cloth, ex- panded metal (Fig. 13), and perforated metal (Fig. 14) are the most familiar kinds of metal lathing. These metal lathings are made in strips or sheets which are cut to the proper dimensions FIG. 13. EXPANDED METAL LATHIXG. and applied to the ceiling-joists and partition- studding by the lather who fastens them with nails or with wire clips of some form. The purpose of lathing, as already stated, is to form a ground to receive and hold plaster. Plas- ters for interior work may be divided into lime plasters and hard-wall plasters, and hard-wall plasters are susceptible of division into natural cement plasters and chemical or patented plas- FIG. 14. PERFORATED METAL LATHING. ters. Lime plaster is composed of quicklime, sand, and hair, or some fine fibre. For the Ijest lime plasters the proportion of the ingredients is generally about one part lime and two parts sand, with 1% bushels of hair to each 200 pounds of lime. The mixing of lime plaster is usually done on the building-site; but in some of the large cities there are special' establishments whose business it is to mix plaster by machinery and furnish it to builders ready for use. The general mode of procedure in mixing lime plas- ter on the building-site is as follows: The lime is first slacked in a tight box by adding water and then the hair is added and thoroughly in- corporated with the lime; lastly, the sand ia added and thoroughly mixed with the lime and hair. Usually, the whole process occupies but one or two hours; but to get the very best plas- ter possible, the slacked lime should be allowed to stand from twenly-fcnir hours to seven days be- fore the hair and sand are added, and then the mixture should stand about a week; it is then
