Ceilings

CEILINGS Fig. 96 also shows the method of supporting a ceiling made of metal lath or sheathing. This sheet material is wired securely to the light bars shown running transversely across the I-beams. The bars are held to the flanges of the I-beams by clamps, the top part of the clamp being bent over the flange and embedded in the concrete. Plaster is placed directly on the metal lath. This same method of fireproofing is also applied to the rafters.

In the case of the Vaughan system shown in Fig. 79, the lower part of the concrete beams forms the ceiling. These may be finished by the application of a single coat of rough plaster, and then the final finishing coat.

Fig. 102 shows the plaster applied directly to the under side of floor-slabs. These slabs are generally of sufficient roughness from the forms so that they will hold the plaster.

In

this same figure is illustrated a ceiling formed by a smooth floor-slab. Care in manipu lation of the concrete, together with well-made forms of planed boards, tongued-and-grooved and well jointed, will produce a fairly smooth surface. The concrete must be wet, and well

worked over with a shovel or hoe when it is placed on the forms, in order to get the larger parts of the aggregate away from the boards, and allow the mortar to sink down and form a smooth face to the mass. Figs. 97 and 98 show the method of forming ceilings for arched floors where some form of close-mesh sheet fabric is used for a reinforcing agent. In Fig. 98, the method of protecting the bottom flanges of I-beams from fire is shown. The rib-lath or ex panded metal is placed about the bottom flange as a kind of cage, fastened in place securely, and plastered over with a thick coating of cement plaster. As before stated in an earlier chapter, the steel reinforcing materials should be em bedded from to inches, depending upon the importance of the member and the likelihood of a hot fire in the room.