inorganic materials, exposure to the weather is much less serious than with organic felts. For an expected use of not more than 4 years, no treatment is necessary. Manufacturers of asbestos felts usually do not recommend recoating asbestos-felt roofs at any time. However, recoating of these roofs with asphalt emulsion at a rate of 3 gallons per square, at intervals of 4 or 5 years, will prolong their usefulness indefinitely.

On mineral-surface built-up roofs, exposed felts are repaired by first removing all dust and dirt from the exposed area and, in the case of asphalt roofs, applying one thin coat of asphalt primer. When the primer is dry, treat as described for exposed bituminous coating. Coal-tar pitch roofs are treated similarly, except that no primer is required before the coal-tar pitch is applied.

On organic felt, smooth-surfaced built-up roofs, repairs to exposed felts should be made as described for those on mineral-surfaced roofs, except that 20 or 25 pounds of asphalt should be mopped per square and the mineral surfacing omitted.

DISINTEGRATED FELTS. - To repair felts that have been exposed and partially disintegrated, scrape off all surfacing material to at least 2 1/2 feet beyond the area of disintegrated felts. Remove disintegrated felt layers and replace them with new 15 - pound, bituminous - saturated felts of approximately the same size, mopped in place with hot bitumen. Apply at least two additional layers of 15-pound saturated felt, mopped on with hot bitumen and extending at least 12 inches beyond the area covered by the replacement felts. Apply a pouring of hot bitumen to the repaired area at a rate of 70 pounds per square; and while hot, embed fresh gravel or slag into it.

As mentioned earlier, asphalt and coal-tar pitch are not compatible. Asphalt and asphalt-saturated felt should always be used in the maintenance of asphalt built-up roofs and coal-tar pitch and coal-tar saturated felt in the maintenance of coal-tar pitch built-up roofs.

Metal Roofing

Galvanized-steel and aluminum roofing should be inspected semiannually for holes, looseness, punctures, broken seams, inadequate side and end laps, inadequate expansion joints, rust or corrosion, and damage resulting from contact of dissimilar metals. Because the different metal roofing materials normally require different preventive maintenance, they are considered separately in this manual. However, copper, terne, and aluminum roofs have one thing in common. When they have been well applied and adequately maintained, reroofing is seldom required.

GALVANIZED - STEEL ROOFING. - Corrugated, galvanized roofing is the lowest in cost of all types of metal roofing; and when properly applied and maintained, it renders satisfactory service. This type of galvanized roofing is used most frequently on warehouses and sheds. It is representative of the galvanized-metal roofings. The most frequent causes of failure in galvanized roofs are improper application and lack of maintenance painting. Leaks at seams and fasteners are evidence of improper application.

Inadequate laps in galvanized-steel roofing may be repaired by caulking or, in severe cases where caulking is not possible, by covering the laps with a membrane, such as asphalt-saturated cotton fabric or lightweight, smooth-surfaced roll roofing. When making repairs, the procedure requires that you adhere to the following steps:

1. Apply an asphalt roof coating to the seams in strips approximately 6 inches wide. Use approximately 1 gallon of coating material to 80 linear feet of seam.

2. Cut the roll roofing or saturated fabric into 4-inch strips approximately 12 feet long. Embed the membrane strip in the asphalt roof coating, pressing it firmly into the coating until it lies flat without wrinkles or buckles; the center of the strip must be directly over the exposed edge of the roofing.

3. Then apply another coating directly over the membrane strip so that the membrane is completely covered and the first and second coatings are continuous.

Roof coating materials vary considerably in consistency, composition, and setting time. In some cases, it may be desirable to allow the first coating to become tacky before applying the membrane material or to allow the first coating with the membrane embedded in it to remain for some time before applying the second coating.

You should realize that repairs of this kind cannot be expected to last as long as the galvanized sheets. Seams treated by this method should be maintained by recoating them periodically with an asphalt coating of the type used in the original treatment. [n warm humid locations, recoating will probably be necessary after