CEMP-ET
TI 809-53
01 May 1999
(b) For a glaze coat the bitumen is mopped or squeegeed at a rate of 1 kg/m2 (0.2 psf) or
less. This is far less durable than a flood coat and aggregate.
(c) A cutback coating is a solvent-based roof coating available with or without reinforcing
fiber, similar to a glaze coat.
(d) An emulsion coating is an asphalt dispersion in water using a clay stabilizer. It is
available with or without reinforcing fibers. Emulsions are more durable (sun and water-resistant) than
glazings and cutbacks and provide better flame spread ratings. They cannot be stored or applied in
freezing weather.
(e) Aluminized coatings (either fibrated or non-fibrated asphalt aluminum coatings) are
popular on sloped surfaces but dull quickly on roofs that pond water. Reduction in solar loading and
increased UV protection can be expected; recoating at 5-7 years is needed to restore protective
qualities.
(f) Water-based asphalt-aluminum coatings are relatively new. Water mixed with fine
aluminum flakes may result in hydrogen gas buildup. Storage is limited to about 6-months.
(g) Reflective latex-based coatings using acrylic elastomers are also available. As with
emulsion coatings, they should be stored and applied under warm conditions only. They also require
positive drainage for best performance.
(h) Some cold process systems spray an asphalt cutback onto the roof surface followed
by blown roofing granules. Approximately 2 kg/m2 (0.4 psf) of granules is applied.
k. Penetrations and Flashings. Flashing and detailing of BUR systems is critical. Construction
Detail plates are available from the NRCA, SMACNA, and individual manufacturers. Pitch pockets and
embedded metal gravel stops are especially troublesome and should be avoided by using raised curbs
and edges whenever possible. Polymer modified bituminous materials are frequently used as flashings
for BUR systems as they are tough, flexible and durable. However, they require careful workmanship
as well. The MB and BUR materials should be from a single manufacturer.
l.
Historical Roof Restoration. BURs are suitable for historical renovation.
m. Aesthetics. In typical low-slope applications aesthetics is rarely of concern. Aggregate is
relatively attractive with some color choices available. Mineral capsheets and sprayed granule roofing
provide some light reflectance and when carefully installed, can look good. Reflective coatings are
pleasing while fresh but can become quickly objectionable if they flake off, dull unevenly, or craze due
to substrate movement. BURs can also be converted into PMR plaza decks (when combined with
extruded polystyrene insulation, filter fabric, and paver-ballast) for an attractive appearance.
n. Gaps, Flashings and Sealants.
(1) Gaps. Gaps in insulation in excess of 6 mm (1/4 in.) should be filled in by inserting pieces
of thermal insulation or by replacing broken boards. Gaps in nailable decks are bridged with sheets of
galvanized steel.
(2) Flashings.
(a) Vertical flashings on BUR systems require cant strips to reduce the angle at the base
of the wall or curb. NRCA details, on occasion modified to specific job conditions, should be followed.
(b) Base flashings should extend not less than 200 mm (8 in.) above the membrane.
4-5
Previous Page
