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 CASE A6 - Roofing and Waterproofing, C. B. Key
Problem: Blistering of built-up roofing when applied over polyurethane roof
insulation.
Collection of Facts: In the latter seventies, many built-up roofs applied
over polyurethane insulation were noted to produce blisters at the interface
between the insulation and the first layer of felt. The blistering was
believed to be caused by moisture in the facing felt of the insulation or
offgasing of the polyurethane insulation. None of these theories were ever
proven.
Solution: This problem is eliminated by placing a thin layer of fiberous
glass, perlite board, or mineral fiber board insulation between the
polyurethane insulation and the first layer of roofing felt. It is purely
academic to prove whether the cause of blistering is offgasing or moisture
vapor. However, a porous insulation, in contrast to a closed cell insulation
like polyurethane, allows any gaseous or vapor pressures to dissipate
laterally and reduce the concentrated effect that caused the blistering.
CASE A7 - Roofing and Waterproofing, C. B. Key
Problem: Determining the correct temperature for heating asphalt used in
built-up roofing.
Collection of Facts: Until the oil embargo in the early seventies, imperial
temperatures specified in ASTM D-312 were satisfactory for heating asphalt for
use in built-up roofing without producing any adverse effects. However, when
we began acquiring oil from different sources, the asphalt derived from these
crudes produced unreliable characteristics when heated in accordance with
these imperial temperatures. This often resulted in lowering the softening
point of the asphalt because it was heated above the actual temperature
required. The results were that the asphalt and roofing membrane would slide
down the roof. Some asphalts also required hotter temperatures than
recommended in ASTM D-312 to obtain proper adhesion.
Solution: It was determined in the roofing industry that a more reliable
method of obtaining the right temperature at which asphalt should be heated
for proper application was based on viscosity. The concept of Equiviscous
Temperature (EVT) has replaced the use of imperial temperatures in the roofing
industry. The EVT is the temperature at which the viscosity is 125
centistokes when tested in accordance with the requirements of ASTM D-2170.
The proper temperature for application of asphalt is a range between
twenty-five degrees Fahrenheit above the EVT and twenty-five degrees
Fahrenheit below the EVT. Asphalt manufacturers' labels or bill of lading are
now required to provide the EVT.
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