repairs because asphalt and coal-tar pitch are not
compatible and contact between the two should be avoided.
If you are in doubt, perform a volubility test.
The SOLUBILITY TEST is performed by pouring
white gasoline into a container to which a small amount of
unknown bituminous material is added. The amount that
will stick to the head of a nail will be sufficient. The
mixture is then agitated to determine the volubility of the
unknown material. If the material mixes readily, giving a
homogeneous mixture, it is an asphalt cement. If a mixture
with stringy particles in suspension results, it is a tar, since
tars are insoluble. If the unknown material is not readily
soluble but forms black globules (balls), it is an asphalt
semiannually for cracking, alligatoring, low spots, and
water pending; exposed bituminous coatings; and exposed,
disintegrated, blistered, curled, or buckled felts.
CRACKING AND ALLIGATORING. Smooth-
surfaced, asphalt built-up roofs on which the surface
mopping is relatively thin usually show definite alligatoring
of the surface coating within 3 to 5 years. Alligatoring is
always most severe where the asphalt coating is thickest. If
allowed to proceed, alligatoring will develop into cracking,
as shown in figure 7-9. Once the surface coating is cracked,
water penetrates the membrane; and the roof deteriorates
rapidly. Consequently, maintenance is necessary to prevent
The type and extent of maintenance depend on the
future use of the structure. On smooth-surfaced, organic
felt roofs of relatively brief expected use (4 years or
less), remove all dust and dirt by sweeping, vacuuming,
or air blasting and apply a thin coat of asphalt primer.
After the primer is dry, one or two coating materials
(asphalt or asphalt emulsion) may be applied by
brushing or spraying at a rate of 3 gallons per square
(100 square feet).
If the asphalt coating is alligatored but not cracked
and the felts are not exposed, the primer may be
omitted. If an asphalt emulsion coating is to be applied
to such surfaces, dust and dirt maybe washed off with a
stream of water from a hose. The emulsion can be
applied to a damp but not a wet surface.
On organic (rag) felt roofs intended for prolonged
use (over 4 years), the cleaning and priming
requirements are the same as for roofs of relatively brief
expected use. After the primer has dried, apply one coat
of asphalt emulsion at a rate of 2 gallons per square.
Immediately after applying the emulsion while it is still
wet, embed strips of fibrous glass mesh (woven or
nonwoven) in the emulsion, lapping the strips 2 inches.
While the first coat of emulsion is still wet, apply a
second coat of emulsion at a rate of 1 gallon per square
over the fibrous glass strips. After the second coat of
emulsion has set firmly, apply a final coat of emulsion
at a rate of 2 gallons per square. If the asphalt surface is
alligatored but not cracked and the felts are not exposed,
the primer may be omitted.
EXPOSED BITUMINOUS COATING. When
the bituminous coating on a mineral-surfaced built-up
roof is exposed, as shown in figure 7-10, brush loose
gravel or slag from the bare area. Cover the bare area
with hot bitumen poured at a rate of 70 pounds per
square, and embed fresh gravel or slag. Old gravel or
slag may be reapplied when the dirt and dust have been
screened from it.
EXPOSED FELTS. Smooth-surfaced, asbestos-
felt built-up roofs may be surfaced originally with hot
asphalt or with a cold-applied asphalt emulsion. After
4 or 5 years of exposure (sometimes earlier with
cold-applied coatings), light gray or even white areas
appear, indicating that the felts are partly exposed.
Because the asbestos felts are constructed mainly of
Figure 7-10.Exposure of bituminous coating.
Figure 7-9.Cracking and alligatoring.