For all of these blocks, mortar composed of lime with a little cement should be used for setting, and the finished plaster surfaces are best when hard-setting plaster -is used.
Metal Lath Partitions. For a saving of floor space, very thin partitions may be made by using small steel bars for studding; these are usually -inch channel bars set vertically about a foot apart and turned at a right angle to be fastened top and bottom. On one side metal lathing is stretched and wired to the bars. This is plastered with a very heavy coat of hard plaster, which squeezes through the lathing and makes a good surface to receive the plaster of the other side side of the parti tion, forming, when completed, a solid wall of plaster and metal about 1 inches thick. (Fig. 237.) It is necessary in this case to use a very hard setting plaster, as this gives the partition its stiffness. Special patented studs of sheet steel, made with prong to hold the lathing, and of various depths, Fig. 238, are used in a similar manner. Door and window frames are set in these thin, partitions, by setting up a rough wooden frame to which the channel bar is screwed, as in Fig. 239, and for a nailing for chair rails, picture mouldings, and other finish, strips of wood are laced to the lathing, flush with the plastering before the plaster is applied. (Fig. 240.) Metal Lathing. Metal lathing, which is of great importance, both for fireproofing, and the finish of fireproof buildings, may be obtained in a variety of patterns and devices. The original form of metal lathing was the common on wire cloth, and this is still one of the prin cipal forms in which metal lathing is found. Improvement in the manu facture of wire cloth for lathing may be found in the various means adopted for stiffening the cloth by rods or ribs of metal. These are attached to, or woven into, the lathing which is then known as "stiffened lathing." A well-known form of stiffened lathing is the Clinton lath, which contains corrugated steel furring strips, attached to the cloth by metal clips and running across the roll every eight inches. These strips not only serve to stiffen the lathing, when stretched over furrings, but, if the lathing is applied directly to a plain surface, such as planking or brick walls, the stiffening keeps the lathing away, and allows room for the clinch of the plaster.
The Roebling stiffened lathing contains V shaped ribs of various depth, which are woven into the cloth at 7•',-inch intervals. These ribs serve for a furring, and are made from if to 11 inches in depth. For special uses, ribs of j--inch steel rods are used instead of the V-shaped steel. Wire cloth for lathing is run in a variety of meshes; 3 X 3 and 21- X 2'- to the inch being the com mon mesh, and it may be obtained plain, painted or galvanized; painted lathing being very satisfactory, and more generally used than any other kind.
Expanded Metal Lathing. This form of lathing is made from strips of thin and tough sheet steel, which are cut at regular intervals and then "expanded" by being wrenched or pushed into open meshes, greater or less, as the cuts are longer or shorter. This expanding also turns the metal on edge, making a flat and stiff sheet of lathing much larger than the original piece of metal. (Fig. 241.) Having a degree of stiffness, this lathing does not require stretching, and it is used extensively for wrapping steel beams or columns for fireproofing or finishing, for thin partitions, and for concrete floors.
An objection is sometimes made to wire or expanded metal laths, that they require an excessive amount of plaster for ordinary uses. This may be overcome, when feasible, by the use of the Bostwick sheet metal lath, shown in Fig. 242. This is made from sheet steel by punch ing out loops at regular intervals. In this, and many other forms of sheet metal lathing, the surface is corrugated, besides being punched, to give stiffness and to keep the lathing away from the face to which it is applied. Sheet metal lathing is easily adapted to the forming of coves or round ners, but for fireproofing the open lathing, requiring a greater amount of plaster, with the metal more thoroughly imbedded, is to be ferred.