21. Asphalt, or solid bitumen, is found in several countries. Asphalt, combined with calcareous earth, that is, earth containing lime, forms a compact, semielastic solid, not liable to injury from the strongest influences of frost or thaw, impervious to water, and unaffected by acids.

22. There are three methods of laying asphalt:

The first and most durable method consists in laying felt en-tirely free from saturation with asphalt, then applying a coat of asphalt in solution, and finishing with a covering of gravel.

The second method consists in laying sheets of felt saturated with asphalt, finishing with sand.

The third is similar to the first, except that the finishing is done with a coating of Portland cement.

23. The application is very much like that in use in other composition roofing, except that the first and third methods call for copper or lead flashings. Two thicknesses of the composite roofing felt is stretched from the eaves to the ridge, the Manila side of the felt being placed downwards, the felt being secured with nails about 2 1/2 feet apart. The entire surface should then receive a coating of natural asphalt cement.

Another thickness of the felt should be laid in the cement, securing it at the upper edge by nails 4 feet apart, lapping each successive sheet about 1 inch over that preceding it. Over the entire surface of the felt thus laid, there should be spread an even and continuous coating of the cement, and this coating should immediately be covered with an adequate body of well screened gravel.

24. The flash-ins for this roof should preferably be of copper, as should also the eaves stops and nails. Flashings of zinc, galvanized iron, or tin may, however, be used as fairly satisfactory substitutes for copper.

Asphalt Roofing 245

Fig. 20.

Asphalt Roofing 246

Fig. 21.

The eaves stops (see a, Fig. 20) should extend 2 inches on the roof as shown at b; they are laid over the felt and should extend down wards over the eaves c not less than 1 inch below the upper surface of the roof boards. The wall flashings a, Fig. 21, extend at least 2 inches under the felt on the roof.

They should be well nailed, and should be covered with cement when the gravel is applied; they should project upwards against the wall at least 5 inches and be secured with flashing hooks, and should have the vertical joints c well locked and soldered.

The flashing should be covered with a coun-ter flashing d, Fig. 21, which reaches within 2 inches of the roof, and is turned in to the wall at least 1 inch and secured by wall hooks or plugging. The joint should be pointed with elastic cement. This roofing may be covered with a layer of hydraulic cement, as shown at a, Fig. 22, 1 1/2 inches thick, divided into small sections b, b suggestive of stone or tile.

Asphalt Roofing 247

Fig. 22.

Asphalt Roofing 248

Fig. 23.

In the second method (see Fig. 23), the flashings are of the same material as the roof. In this method the felt a is laid close in to the angles against the walls, and is extended 2 inches upwards. Over this, in the angles, is laid a strip b 8 inches wide, with half its width against the walls and half on the roof. The upper edge is fastened with a wooden strip c, nailed to the walls and pointed with cement; the felt is pressed in to the angles of the wall and cemented to the roof with liquid coating. In securing the laps of the prepared felt, the nails should be spaced about 1 inch apart.

The outside angles of walls and chimneys should be flashed, as shown in Fig. 24.

A strip of felt a 8 inches wide is folded and cut as shown. It is bent around the angle, and is nailed and cemented, with the liquid coating, over the under roofing b, after which it is counterflashed as shown at c.

The inside angles of walls are flashed, as shown in Fig. 25, the strip of felt a being of the same dimensions and similar to that used for outside angles; the process of applying is the same.

Asphalt Roofing 249

Fig. 24.

Asphalt Roofing 250

Fig. 25.

The ridge is capped with a 16-inch strip of felt, lapping on the roof each side of the ridge, well cemented and securely nailed at the edges and joints. The best temperature to apply this roofing in is one of 35° F. When it is colder than this, the material should be kept in a warm room before using, and taken out only as required.

The quantity of material required to lay and cover a square of this roofing is: 1 roll of 2 or 3 ply natural asphalt roofing; 2 gallons of liquid coating; 1 pound of nails; and 1 pound of tin caps.