Joist hangers are used for framing wood joists into girders and for framing headers into joists around stairwells and chimneys. Various types of expansion bolts, screw anchors, and toggle bolts are available for securing fixtures, brackets, and equipment to solid material, such as masonry, brick, concrete, and stone. Anchors also can be had for fastening to hollow walls, such as plaster on metal lath in furred spaces and hollow tile. The best device to use depends on the requirements in each case. For use with practically any materials, including soft and brittle ones, such as composition board, glass, and tile, fiber screw anchors with a hollow metal core find a universal application. These plugs with braided metal cores possess many advantages: They can be used with wood screws and with lag screws. The flexible construction permits the plug to conform to any irregularities. Because of this elastic compression, the fibers are compressed as the screw enters. Screws can be unscrewed and replaced. Shock and vibration have no effect on gripping power. The plugs come in about 40 sizes to fit anything from a No.6 screw to a 5/8-in lag screw. In practice, a hole is drilled first, the plug is driven into it, and then the screw is inserted, expanding the plug against the sides of the hole. For some fastenings, one-piece drive bolts are hammered like a nail into prepared holes in masonry or concrete. Other types of expansion bolts have expansion shields or are calked into place. The expansion shield is expanded in the hole by a tapered sleeve forced against a cone-shaped nut by the tightening of a bolt threaded into the cone. These types are not recommended for soft or brittle materials. For thin hollow walls, toggle bolts equipped with spring-actuated wings are used (Fig. 11.89). The wings will pass into the hole in folded position. After entering the hollow space, the wings open out, thereby obtaining a secure hold. For fastening lightweight materials to nailable supports, stapling machines are extensively used. In one patented system, for example, staples secure acoustic tile to wood furring strips. In this system, invisible fastenings are obtained by using a full-spline suspension for the kerfed pieces of tile and a special stapling machine adjusted to function at the proper distance below the furring strips. The machine staples the splines (at the joints of the tiles) to the supporting strips, giving a speedy, economical, and secure fastening. Wire nails, made of mild steel, are commonly used for most nailing purposes. Cylindrical in shape, they are stronger for driving than cut nails and are not so liable to bend when driven into hardwoods. Cut nails, sheared from steel plate, are flat and tapered. They have holding power considerably greater than wire nails. They are usually preferred to wire nails for fastening wood battens to plaster; also in places where there is danger that the nails may be drawn out by direct pull. Cut nails are frequently used for driving into material other than wood. They are generally used for fastening flooring. When driven with width parallel to grain of wood, they have less tendency to split wood

Both thermosetting and thermoplastic molding materials are formed into final shape by a variety of molding and fabricating methods. Thermosetting materials are commonly formed by placing molding powder or molded preform in heated dies and compressing under heat and pressure into the final infusible shape. Or they are formed by forcing heat-softened material into a heated die for final forming into the hard infusible shape. Thermoplastics are commonly formed by injection molding, that is, by forcing soft, hot plastic into a cold die, where it hardens by cooling. Continuous profiles of thermoplastic materials are made by extrusion. Thermoplastic sheets, especially transparent acrylics, are frequently formed into final shape by heating and then blowing to final form under compressed air or by drawing a partial vacuum against the softened sheet. Foamed plastics are employed for thermal insulation in refrigerators, buildings, and many other applications. In buildings, plastics are either prefoamed into slabs, blocks, or other appropriate shapes, or they are foamed in place. Prefoamed materials, such as polystyrene, are made by adding a blowing agent and extruding the mixture under pressure and at elevated temperatures. As the material emerges from the extruder, it expands into a large log that can be cut into desired shapes. The cells are closed; that is, they are not interconnecting and are quite impermeable. Foamed-in-place plastics are made with pellets or liquids. The pellets, made, for example, of polystyrene, are poured into the space to be occupied, such as a mold, and heated, whereupon they expand and occupy the space. The resulting mass may be permeable between pellets. Liquid-based foams, exemplified by polyurethane, are made by mixing liquid ingredients and immediately casting the mixture into the space to be occupied. A quick reaction results in a foam that rises and hardens by a thermosetting reaction. When blown with fluorocarbon gases, such forms have exceptionally low thermal conductivities. All the plastics can be machined, if proper allowance is made for the properties

strength, min, psi Moisture content for Type I units, max, % of total absorption (average of 5 units) Avg annual relative humidity, % Moisture absorption, max, lb. / ft3 (average of 5 units) Oven-dry weight of concrete, lb / ft3 Avg of 5 units Individual min Over to Under or more to Under Concrete building brick, N-I, N-II (high strength severe exposures) S-I, S-II (general use, moderate exposures) Linear shrinkage, %: 0.03 or less 45 40 35 0.03 to 0.45 40 35 30 Over 0.045 35 30 25 Solid, load-bearing units, N-I, N-II (unprotected exterior walls below grade or above grade exposed to frost) S-I, S-II (protected exterior walls below grade or above grade exposed to frost) Linear shrinkage, %; (Same as for brick) Hollow, load bearing units, N-I, N-II (general use) 1000 800 13 15 18 S-I, S-II (above grade, weather protected) Linear shrinkage, %; (Same as for brick) Hollow, non-load-bearing units, Linear shrinkage, %; (Same as for brick) *For units weighing less than 85 lb / ft3. TABLE 4.8 Physical Requirements for Clay or Shale Solid Brick