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BITUMINOUS
FLASHINGS |
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8.4.3 Surfacing: JM recommends that GlasTite Flexible
flashing sheet be coated with an approved JM roof coating
such as Topgard Type A, Type B, or Fibrated Aluminum Roof
Coating. Hot asphalt is not an acceptable coating.
8.5 Application of SBS Modified Bitumen Materials
("DFE-" Specifications)
8.5.1 DynaFlex is a durable, flexible, modified bitumen flashing
sheet incorporating a fiber glass scrim/polyester mat
composite reinforcement. This composite reinforcement
provides strength and dimensional stability, as well as
conformability, puncture and tear resistance. DynaFlex can be
installed using hot asphalt, JM MBR Flashing Cement or MBR
Utility Cement. It is not acceptable to heat-weld DynaFlex.
Conventional cut-back cements should not be used to adhere
DynaFlex to the surface being flashed.
8.5.2 A base sheet may be required under the DynaFlex in
some flashing specifications. Typically, this is necessary when
the flashing materials are installed over wood or plywood
substrates.
8.5.3 Hot Bitumen Application
The advantage of hot-applied flashings is speed, economy,
and convenience. The quality of asphalt used is crucial to the
overall success of the flashing system. JM maintains a list of
qualified asphalt sources throughout the United States. These
asphalts meet or exceed the requirements of ASTM D 312,
"Standard Specification for Asphalt Used in Roofing". All
asphalts utilized in the construction of guaranteed flashing
systems must have an Asphalt Confirmation Number indicating
that the asphalt was registered with an approved source.
8.5.4 ASTM D 312, Type III and Type IV asphalts are the only
asphalts acceptable for application of bituminous base
flashings. Low softening point asphalts must not be used, since
flashings placed in these bitumens will sag. PermaMop is not
to be used.
8.5.5 It is crucial that the flashing be firmly and uniformly set in a
full mopping of hot asphalt, without voids and with all edges well
sealed. To ensure that full contact is made, the mechanic must
"work-in" the DynaFlex sheet by applying pressure across the
entire sheet while the asphalt is still hot. If the material is
installed with little or no pressure applied, there is a risk of
disbonding, voids, and openings at the laps.
8.5.6 The temperature of the asphalt at the point of application
is also very important. The asphalt must have a minimum
temperature of 400°F (204°C) or be at the EVT, whichever is
higher, when the sheet is set into it. This will cause the back
coating to remelt or "flux", assuring a proper bond to the
substrate.
8.5.7 All hot-applied flashings must be secured at the top edge
with appropriate mechanical fasteners, spaced 6" (152 mm)
o.c. maximum, or with some other positive means to prevent
sliding or sagging.
8.5.8 The use of short lengths of flashing material
(approximately 6' -8' [1.83 m - 2.44 m]) is strongly
recommended. This will improve handleability of the flashing
material and reduce the possibility of the asphalt cooling too
much before the flashing is laid into it.
8.5.9 During installation of hot-applied base flashing, the
surface to which the flashing will be applied is mopped with the
hot asphalt. The sheet is then laid into place, and "worked-in"
to ensure that it is firmly and uniformly bonded. In cool or cold
weather, the back of the flashing sheet should also be mopped
with the hot asphalt. This "double mopping" has two benefits.
First, it heats up the substrate to which the material will be
applied. Second, it ensures "fluxing" of the back coating on the
sheet which results in a superior bond.
8.5.10 In cold weather, maintaining the desired asphalt
temperature can be difficult. Improper asphalt temperature can
result in adhesion problems. If conditions require that the
application of the modified bitumen continue at temperatures
below 40°F (4°C) additional precautions must be taken. Very
short lengths of flashing (3' - 6' [0.92 - 1.83 m]) should be used.
In addition, the asphalt application equipment should be
insulated to ensure that the asphalt is delivered to the flashing
area at the appropriate temperature.
8.6 Heat Weld Application of SBS Modified Bitumen
Flashings
8.6.1 The advantage of heat welded flashings is the speed at
which they can be applied and their ability to conform to
irregular surfaces. FesCant Plus Cant Strips are required at
the junction between the roof deck and the vertical surface to
be flashed. These cant strips are made of fire-retardant
material and are suitable for use in heat weld applications.
Wood nailers shall be installed at all eaves and openings in the
roof so that roofing plies, edging and gravel stops may be
properly secured. When roof insulation is specified, wood
nailers shall be of the same thickness as the insulation.
8.6.2 Flashing strips shall be of sufficient size to extend a
minimum of 6" (152 mm) onto the roof surface.
8.6.3 The minimum height for flashing is 8" (203 mm) above
the surface of the roof membrane. All flashing must be secured
at the top edge with appropriate mechanical fasteners, spaced
6" (152 mm) o.c. maximum, or with some other positive means
to prevent sliding or sagging. Suitable metal counterflashing
shall be provided to cover the top edge of the base flashing by
a minimum of 4" (102 mm).
8.6.4 It is crucial that flashing be firmly and uniformly set,
without voids and with all edges well sealed. All laps and edges
should be rolled with a rounded edge roller. Check all laps for
adhesion. Lift up any unbonded areas, reheat the area and
press down.
8.6.5 Safety is of primary importance and it is the
contractor’s responsibility to ensure that all relevant
safety precautions are adhered to. (See section 7B.17).
Never heat weld to an area where the flame or heat can be
pulled in. Never heat weld directly to a combustible surface or
to an area that cannot be seen. If there is a question as to the
safety of the area being heat welded, then the heat should be
applied to the flashing material away from the area
