CASE A3 - Roofing and Waterproofing, C. B. Key
Alligatoring of aluminum pigmented asphaltic roof coating
Collection of Facts: Within three months after an aluminum pigmented
asphaltic coating was applied on a smooth surfaced built-up roof, it began
alligatoring. This was a new built-up roof. A glaze coat of asphalt had
been applied to the surface of the built-up roof as a temporary protection
of the felts during construction. The glaze coat of asphalt had not been
left exposed to the weather long enough to oxidize and still possess cold
flow properties. This is what caused the alligatoring in the aluminum
pigmented asphaltic coating.
Solution: The roof coating was allowed to continue alligatoring for
approximately six months, at which time the alligatoring stopped. This is
because the asphalt was allowed to oxidize. The roof was recoated with
aluminum pigmented asphaltic coating and there were no subsequent problems.
CASE A4 - Roofing and Waterproofing, C. B. Key
Wind blown aggregate surfacing on built-up roofing
Collection of Facts: Wind blown aggregate on built-up roofing in Guam
caused damage to automobiles and other structures during typhoons.
Membrane felts were left bare and unprotected from ultraviolet rays of the
sun which deteriorate the felts.
Solution: Double aggregate surfacing was used. The gravel was coated
with a fine spray of kerosene to improve adhesion. The aggregate was
applied in two layers. The first layer consisted of four hundred pounds
of gravel embedded in sixty pounds of hot asphalt per one hundred square
feet. The second layer consisted of three hundred pounds of gravel
embedded in eighty pounds of hot asphalt per one hundred square feet. All
loose gravel was removed.
CASE A5 - Roofing and Waterproofing, C. B. Key
Problem: Poor adhesion and blistering of built-up roofing on high
moisture content decks.
Collection of Facts: When built-up roofing is hot-mopped to high moisture
content decks, e.g., gypsum, lightweight insulating concrete, the roofing
system resulted in poor adhesion to the deck and often resulted in
Solution: Mechanical fastening of an inorganic base sheet or vented base
sheet was found to eliminate this problem. Subsequent plies of roofing
felt were hot-mopped to the base sheet.