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
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
1 5 - p o u n d , b i t u m i n o u s - s a t u r a t e d f e l t s o f
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
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.
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
G A L V A N I Z E D - S T E E L
R O O F I N G .
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
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