169. Ceilings

Ceilings. Before plastering the ceiling under flat arches, any inequalities should be filled with mortar, so as to make a flat surface. It is usual to apply two coats of plaster directly to the under side of the arches. If furring is necessary for fastening decorative work, etc., it may consist of either wood or metal strips, attached by bolts to the bottom of the arches, and covered with wire lathing.

170. Floors

Floors. In nearly all systems of construction, concrete filling is laid upon the tile, to level up to the top of the I beams; upon the latter are then placed nailing strips, or sleepers, usually 16 inches apart, to which the flooring is fastened. These are made of thoroughly seasoned pieces about 2 inches thick, 4 inches wide at the bottom, and 2 inches at the top. Sometimes 3"x4" pieces are used, the under side being notched 1 inch, to fit over the upper flange of the beams. A common practice is to allow 3 1/2 inches between the top of the I beams and that of the floor, in order to insert water and gas pipes, electric wiring, etc. The strips are usually laid at right angles to the beams, and fastened to them by iron clamps, one end of which is hooked under the top flanges, and the other driven into the side of the strip. If the strips are laid parallel to the beams, pieces of flat iron, about 1/8 in. X 2 in. and 1 foot long, are nailed across the under side of the strips, about 4 feet apart, to hold them firmly in place. When the sleepers are laid, concrete is filled in between them, flush with the tops, the beveled sides of the strips holding them in position.

171. As lightness is of prime importance in floor construction, the concrete should weigh as little as is possible for good work. This result may be obtained by using some light, porous material, such as cinders, etc., in place of broken stone. The cinders, free from dirt, should be mixed with cement or lime mortar, and the concrete should be laid compactly on the arches, being allowed to dry before the flooring is laid. To save the time required for drying, the cinders are often put on dry, but this is a practice not to be recommended. When the beams are very deep, tile of a less depth is sometimes used, and the filling consists of partition tile or specially made ∩ -shaped tile.

Office buildings frequently have a great many movable partitions, to suit the requirements of tenants. In such cases, the wooden floors are laid over the whole floor space, and the partitions placed on them; but, if the latter are to be permanent, they should be put in position before the floors are laid.

170 Floors 209

Fig. 82.

172. Fig. 82, representing the floor construction in a large Chicago building, well illustrates the foregoing descriptions. At a is shown the steel column, formed of Z bars and plates, carrying the girder b, and the floorbeams c; at d are the tile arch blocks; at e, the 2"x4" nailing strips; at f, the concrete filling; at g, the wooden flooring; at h, the water and gas pipes; and at j, the tile fireproofing and plastering around the column.