Installation Guide

9
Condition
CRACKS (cont.)
Cracks At Wall Or
Ceiling Angles
Cracks Not Due To
Any Of The Previously
Mentioned Causes And
Are Not The Result Of
Structural Movement
SURFACE DEFECTS
Fuzz (Efflorescence) On
Surface, White Or Colored,
Is Water Soluble And Can
Be Removed By Brushing
Streaky Discoloration
Streaked Finish, Joinings
Showing, Dirty Areas
Blisters On Finish Coat
(Entrapped air between
finish and substrate)
Projections On Surface
Which Fall Out Leaving
Craters Or Pits. May Have
Fine Cracks Radiating
From The Center
Construction
1. Plaster over gypsum lath.
2. Plaster over masonry.
1.
Plaster over metal or
gypsum lath.
2. Plaster over metal or
gypsum lath on steel
framing.
Basecoat or finish coat over
masonry or concrete substrate.
Lime putty finishes gauged
with gauging plaster or
Keene’s cement.
Finish plaster over any
substrate.
Gauged lime putty or mill
mixed gypsum plaster trowel
finishes.
Finish or basecoat plasters
containing lime.
Probable Cause
1. a. Thin plaster.
b. Failure to use expanded
metal reinforcement.
c. Structural movement.
2. Failure to tie walls
together.
1. a. Metal lath too light.
b. Metal lath not lapped
or properly tied.
c.
Thermal shock.
2. a.
Improper spacing of
framing members.
b. Thermal shock.
Efflorescence – water soluble
salts are deposited on the
surface of the plaster as the
masonry or concrete dries.
1. Use of too much water
while troweling.
2. Improperly/poorly mixed
lime and gauging material.
3. Dirty tools, water, or mixing
equipment.
4. Efflorescence.
1. Too much water used
while troweling.
2. Use of dirty water during
troweling.
1. Basecoat too green (wet).
2. Insufficient suction.
3. Too much water used
while troweling.
4. Insufficient gauging.
5. Troweling before suf-
ficient take-up.
Unslaked lime or foreign
matter in the plaster which
hydrates and expands after
application.
Preventive Action
1. a. Be sure proper plaster-
ing grounds are in place.
b. Always apply expanded
metal reinforcement in all
interior angles.
c. Follow proper construc-
tion practices.
2. Follow proper construction
practices.
Follow proper construction
practices.
Fur wall away from the
masonry or concrete prior to
plastering.
1. Use proper amount
of water while troweling.
2. Thoroughly mix the lime
and gauging.
3. Use only clean tools, mixing
equipment and water.
4. See prevention for FUZZY
surface.
Use only the proper amount
of clean water during trow-
eling.
1/2. Allow basecoat to dry
sufficiently to develop
proper suction.
3. Dash water on surface
sparingly during troweling.
4. Use proper proportions of
lime putty and gauging.
5. Allow plaster to take-up
sufficiently before troweling.
Use Type S hydrated lime or
properly soak lime to insure
proper hydration.
Corrective Action
1. a. Apply second coat of
plaster to proper thickness.
b. Cut out plaster and
patch.
c. Patch cracks.
2. Patch cracks.
1. a/b. Remove lath and
plaster, apply proper
weight lath and replaster.
c. Patch cracks.
2. a. Remove plaster, properly
space framing and replaster.
b. Patch plaster.
Eliminate the source of
moisture.
1–3. Paint plastered surfaces
with a good quality paint
as recommended by the
paint manufacturer.
4. See correction for FUZZY
surface.
Prime and paint surface
with a good quality paint as
recommended by the paint
manufacturer.
Remove blistered finish and
replaster.
Remove the core of the
crater or pits and patch
with finish plaster or ready
mix joint compound.