Surfacings can serve one or more functions for low-slope
membrane roof systems. Surfacings' primary purpose is to protect
membrane roof systems from the effects of ultraviolet rays and
weather exposure. However, surfacings also can provide increased
fire resistance and impact resistance, aesthetic enhancement and
improved roof system thermal performance.
Surfacings can be an integral factory-applied element of a
membrane or a separate field-applied component of a roof system.
Membrane surfacings come in various forms, including aggregate,
ballast, mineral granules, liquid-applied coatings, metal foils,
green roof overburden and an occasional combination.
Factory-surfaced membranes include metal foils, mineral granules,
coatings and granule-coating combinations. Field-applied surfacings
include aggregate, ballast, mineral granules, coatings and green
Aggregate is used to surface built-up and polymer-modified
bitumen roof systems. When used in this context, aggregate is
embedded on a roof surface using hot bitumen or—less
frequently—cold mastic. Aggregate generally is 3/8 to 3/4 of
an inch in diameter river gravel, crushed stone or slag. Gravel and
crushed stone, such as Merrimac gravel, marble chips, geo rock and
green garnet, may be used for decorative purposes. Mineral granules
also can be broadcast into mastic as a field-applied surfacing.
Ballast also is used to surface loose-laid, ballasted single-ply
roof systems and protected membrane roof systems. Ballast generally
is 1 to 2 1/2 inches in diameter aggregate, as differentiated from
built-up roof aggregate, or concrete roof pavers. Ballast also can
be used for decorative purposes and designed to provide or enhance
a roof system's...
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