This section is from the book "A Treatise On Architecture And Building Construction Vol3: Stair Building, Ornamental Ironwork, Roofing, Sheet-Metal Work, Electric-Light Wiring And Bellwork", by The Colliery Engineer Co.. Also available from Amazon: A Treatise On Architecture And Building Construction.
25. Asbestos is a white, gray, or green-gray fibrous variety of amphibole, usually one containing but little aluminum, trenolite, or actinolite; also, improperly, a fibrous serpentine or chrydolite. The fibers are sometimes very long, easily separable, and flax like, sometimes compact and capable of a high polish. It is very soft when reduced to powder. It is incombustible, and from white, green, and gray, turns red and black. Asbestos is mined in Canada, Vermont, Virginia, South Carolina, and Staten Island, N. Y.
26. Before the application of asbestos, the roof surface should be cleaned of all refuse. Care should also be taken that the joints of the boards are planed to a level surface and then thoroughly swept.
Unroll the roofing as shown in Fig. 20, taking care that the material passes over and not under the roll. Cut enough off the roll to cover the length required. Commencing at the eaves, lay the sheets in succession parallel to the eaves. The lap for steep roofs should be 1 1/2 inches, and for flat roofs, 2 or more inches. Where short lengths are used, see that the vertical joints do not come in line with each other; and on steep roofs, where the roofing is vertical, or from ridge to eaves, place a continuous strip next to the short lengths. All edges and laps are cemented before being nailed down, the nails being spaced 1 inch apart. When the roofing has been nailed, cement a second time, thoroughly covering the joints and laps, concealing all nail heads and filling up the edges as much as possible. Next apply a coating to the entire surface of the roof, and when thoroughly dry, apply a second coating, finishing, while fresh, with an even covering of fine ground asbestos powder.
Where there are no gable walls, the roofing is thoroughly cemented at the edge of the roof, with a coating mixed and thickened with hydraulic cement. It should, also, be nailed down close and tight and then covered with a wooden cap molding a, as shown in Fig. 27.
27. Where there are parapet walls, chimneys, bulkheads, etc., the roofing should run to the angle only. See Fig. 28. When the roofing has been nailed in place, the angle formed by the roof and walls should be thoroughly cemented. While this coating of cement b is wet, apply a separate flashing c, as shown; this flashing to be 8 inches wide, 4 inches on the roof and 4 inches up against the walls, nailed and also cemented.
Where a metal counterflashing is used, secure the upper edge of the flashing c, just mentioned, with a wooden strip d, well nailed to the walls, finishing the top with a good coating of cement e. By using a wide strip of wood, and keeping the top of it flush with a joint f in the brickwork, the mortar can be raked out and the coating of cement made to enter the joint, thus rendering it more secure and water-tight.
Apply tin, copper, or zinc, where used for counterflashings, in the same manner as in other roofs. In fitting around the corners of chimneys, etc., take a piece of roofing 8 inches square, and from the middle point of either side, cut it half across; bend this on theangles as required and cement well. This pattern will suit an outside or an inside angle. See Figs. 24 and 25. Where the roofing connects with tin, or other metal portion of the building projecting through the roof, the edges should be carefully secured by nailing and cementing.
28. At the leader outlets (see Fig. 29), turn the leader sleeve over the gutter; cut a piece of roofing felt a with a hole in it the size of the outlet; place this over the sleeve's edge; then cement and nail in place. If the gutters are to be lined with the roofing felt, use a separate strip b in the trough, and put it in place before applying the material c on the roof proper. Nail and cement all the edges and laps, and give an extra coat of cement. Avoid forming sharp angles in the roofing felt, and take care not to injure the material while applying it to the roof.
29. See that all laps are made with the current, or pitch, of the roof. Large roofs should have a pitch of not less than 1 inch to the foot. This roofing should not be applied when the temperatiire is below 40°. With this method, it requires to cover a square: 1/2 roll of roofing material, 1 1/2gallons of coating, and 1 1/2- pounds of nails.