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BITUMINOUS
FLASHINGS |
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8.3.4 Cants: Prior to application of base flashings, a cant strip
shall be installed to modify the sharp angle between the roof
deck and the vertical element of the structure. Minimum size of
the cant shall be 2 ¾ " (70 mm), as measured on the diagonal
face of the cant.
8.3.5 Roof Edging Nailers: Wood nailing strips (pressure
treated with a salt preservative) must be provided to serve as a
base for attaching the flanges of metal edgings. Treatment of
the nailers with creosote or asphaltic preservatives is not
acceptable. The wood nailers must extend horizontally beyond
the flanges of the metal edgings.
8.3.6 Roof Membrane: All felts comprising the roof
membrane shall be installed before the flashing is applied and
shall be turned up the wall or parapet as called for in the
flashing specification. Roofing felts should not be carried all the
way up a wall to act as a base flashing.
8.4 Application of BUR Materials ("FE-" Specifications)
8.4.1 Hot Bitumen Application: GlasTite Flexible(e.g., FE-1)
GlasTite Flexible is an asphalt-coated flashing sheet with a
fiber glass scrim/polyester mat composite reinforcement. The
fiber glass in the reinforcement provides strength and
dimensional stability, while the polyester provides
conformability and resistance to puncture and tearing.
Base flashing materials of this type are typically applied in a
mopping of hot bitumen. The advantage of hot-applied
flashings is speed, economy, and convenience. The quality of
bitumen 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 bitumens utilized in the
construction of guaranteed flashing systems must have an
Asphalt Confirmation Number indicating that the bitumen was
registered with an approved source.
ASTM D 312, Type III and Type IV asphalts are the only
bitumens acceptable for application of bituminous base
flashings. Coal tar and low softening point asphalts must not be
used, since flashings placed in these bitumens will sag. It is
crucial that the flashing be firmly and uniformly set in a full
mopping of hot bitumen, without voids and with all edges well
sealed. To ensure that full contact is made, the mechanic must
"work-in" the flashing sheet by applying pressure across the
entire sheet while the bitumen 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.
The temperature of the bitumen at the point of application is
also very important. The bitumen must be at or slightly above
the EVT when the sheet is set into it. This will cause the back
coating of the flashing sheet to remelt or "flux", assuring a
proper bond to the substrate.
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.
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 bitumen cooling too much before the flashing
is laid into it.
During installation of hot-applied base flashing, the surface to
which the flashing will be applied is mopped with the hot
bitumen. The sheet is then laid into place and "worked-in" to
assure 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 bitumen. This "double mopping" has two benefits.
First, it heats up the substrate to which the material will be
applied. Second, it assures "fluxing" of the back coating on the
sheet, which results in a superior bond.
In cold weather, maintaining the desired bitumen temperature
can be difficult. Improper bitumen temperature can result in
adhesion problems. If conditions require that the application of
the flashing 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, all
of the bitumen application equipment should be insulated to
ensure that the bitumen is delivered to the flashing area at the
appropriate temperature.
In certain circumstances, GlasTite Flexible may also be applied
using cold flashing cement. Refer to the individual flashing
specifications for guidance.
A fiber glass ply felt can be used with reinforced base flashing
as a backer felt. This backer felt is applied to the primed
masonry surface in a mopping of hot bitumen. The use of a
backer felt may be a requirement for the issuance of a
guarantee.
8.4.2 Cold Application: Ply felt and Flashing Cement (e.g.,
FE-2) This system consists of alternating layers of ply felt, set in
and covered over with layers of flashing cement. The ply felt
provides reinforcement to the system, as well as stabilizes the
flashing cement.
The flashing cement serves as an adhesive for the flashing
plies, and provides the interply waterproofing.
Bestile Industrial Roof Cement: This cold application
flashing cement is a blend of selected asphalts, non-asbestos
fibers, selected fillers and petroleum solvents. It is supplied in a
smooth, easy working consistency which adheres to wet and
dry surfaces, resists slumping and remains plastic. Bestile
Industrial Roof Cement may be used on horizontal as well as
vertical surfaces and where differential movement is expected.
It provides excellent durability against the stresses and wear to
which flashing adhesives are normally exposed.
