International Building Code 718.1
Thickness of plaster. The minimum thickness of gypsum
plaster or portland cement plaster used in a fire-resistance-
rated system shall be determined by the prescribed fire
tests. The plaster thickness shall be measured from the face of
the lath where applied to gypsum lath or metal lath.
International Building Code 718.2
Plaster equivalents. For fire-resistance purposes, 0.5
inch (12.7 mm) of unsanded gypsum plaster shall be deemed
equivalent to 0.75 inch (19.1 mm) of one-to-three gypsum sand
plaster or 1 inch (25 mm) of portland cement sand plaster.
International Building Code 718.3
Noncombustible furring. In buildings of Type I and II
construction, plaster shall be applied directly on concrete or
masonry or on approved noncombustible plastering base and
International Building Code 718.4
Double reinforcement. Plaster protection more than 1
inch (25 mm) in thickness shall be reinforced with an additional
layer of approved lath embedded at least 0.75 inch (19.1
mm) from the outer surface and fixed securely in place.
Exception: Solid plaster partitions or where otherwise
determined by fire tests.
International Building Code 718.5
Plaster alternatives for concrete. In reinforced concrete
construction, gypsum plaster or portland cement plaster is
permitted to be substituted for 0.5 inch (12.7 mm) of the
required poured concrete protection, except that a minimum
thickness of 0.375 inch (9.5 mm) of poured concrete shall be
provided in reinforced concrete floors and 1 inch (25 mm) in
reinforced concrete columns in addition to the plaster finish.
The concrete base shall be prepared in accordance with Section