Installation Guide

10
Condition
WEAK OR SOFT PLASTER
Soft, White, Chalky
Surface
Soft, Dark, Damp
Plaster Surface
Weak, Soft Plaster,
Due To Improperly
Proportioned Aggregate
Separation Of Basecoat
From Gypsum Lath
Separation Of Basecoat
From Metal Lath
Separation Of Basecoat
From Unit Masonry
Construction
Basecoat over any
plaster base.
Basecoat over any
substrate.
Gypsum basecoat over any
plaster base.
Basecoat over gypsum lath.
Basecoat over metal lath.
Basecoat over unit masonry.
Probable Cause
Usually occurring during
dry, hot weather. Too much
ventilation has removed water
from the plaster before it
has set. Called “dry-out”.
1. DAMP WEATHER - too
little ventilation during
damp weather, water
remaining in plaster
too long after set has
occurred, “Sweat-Out”.
2. FREEZING WEATHER
CONDITIONS – FROZEN
PLASTER
1. Too fine or poor aggre-
gate grade.
2. Too much aggregate.
1. Too much or improper
aggregate used.
2. Frozen plaster.
1. Too much or improper
aggregate.
2. Frozen plaster.
3. Scratch coat too thin.
1. Excessive suction of the
masonry base.
2. Masonry base has a
non-absorbent or glazed
surface.
3. Efflorescence present on
the masonry base.
Preventive Action
Screen openings to minimize
drafts during dry, hot weather
and spray the surfaces and
floors with water during the
setting period.
1. Maintain proper heating
and ventilating prior to,
during and after plastering.
2. Maintain minimum 55˚F
prior to, during and after
plastering and provide
adequate ventilation until
plaster is dry.
Use only aggregate meeting
ASTM specification. Properly
proportion aggregate and
plaster.
1. Use only proper and
ASTM-specified plaster/
aggregate proportions.
2. Maintain a minimum temper-
ature of 55˚F in the building
prior to, during and after
application and provide
adequate ventilation.
1. Use only proper and
ASTM-specified plaster/
aggregate proportions.
2. Maintain a minimum
temperature of 55˚F in the
building prior to, during and
after application and pro-
vide adequate ventilation.
1. Dampen the masonry to
reduce suction.
2. Roughen the masonry
surface to provide a key
for the plaster.
3. Eliminate the source of
moisture causing the efflo-
rescence. Fur away from
the masonry surface and
apply lath over the furring.
Corrective Action
Spray dried out areas with
water or a solution of alum
(1 lb. alum per 3 gallons of
water).
1. Dry plaster by ventilating
and heating. If condition
has existed for too long
it cannot be corrected.
Plaster must be removed
and replastered.
2. Close building, heat
building until plaster sets
and continue heating
and ventilating after set.
No correction – remove the
plaster and replaster.
No correction – remove the
plaster and replaster.
No correction – remove the
plaster and replaster.
No correction – remove the
plaster and replaster.
BOND FAILURE OF BASECOAT