Installation Guide

11
Condition
Separation Of Gypsum
Plaster From Monolithic
Concrete Surface
Brown Coat Plaster
Separating From
Scratch Coat Plaster
FINISH COAT PROBLEMS
Gauged Lime Putty
Finish Coat Separating
From Brown Coat Plaster
Gypsum Sand Float Or
Trowel Finish Separating
From Brown Coat
Finish Coat Weak, Soft
Lime/Gauging Finish –
Tough, Short Working
Or Lumpy Lime Putty
Set Not Uniform
Construction
Basecoat over monolithic
concrete.
Three-coat plaster work.
Gauged lime finish over
basecoat.
Gypsum sand finish over
basecoat.
Gypsum finish over basecoat.
Gauged lime finish over
basecoat.
Gypsum finish over
basecoat.
Probable Cause
Concrete bonding agent not
applied.
1. Weak scratch coat plaster.
2. Failure to provide adequate
mechanical keying to
scratch coat.
1. Brown coat too weak,
too smooth, too wet (too
little suction) or too dry
(too much suction).
2. Finish applied improperly.
3. Incomplete hydration of
finish lime.
1. Brown coat too weak.
2. Brown coat too dry.
3. Brown coat too smooth.
1. Insufficient gauging
plaster used.
2. Retempered finish coat.
3. Inadequate or insufficient
troweling of the finish.
1. Old material, warehoused
too long or improperly.
2. Lime improperly mixed or
soaked.
3. Low temperatures.
1. Improper gauging plaster
used.
2. Temperature conditions
too hot or cold.
Preventive Action
Apply plaster bonding agent
per ASTM specification –
before application of plaster.
1. See preventive actions
under weak, soft plaster.
2. Do not over trowel scratch
coat; rake or broom scratch
coat to provide mechanical
keying.
1. Make sure brown coat
is properly prepared to
receive finish.
2. Apply finish, taking pre-
cautions to follow recom-
mended practices.
3. Use only Type S hydrated
lime and mix according
to recommendations.
Make certain that the brown
coat is sound, not overly dry
and has adequate roughness
to provide keying to the finish.
1. Use proper proportions
of gauging to lime putty.
2. Do not retemper plaster
that has started to set.
3. Lime putty finishes must
be troweled sufficiently
to densify the finish and
develop proper strength.
1. Use only fresh lime which
has been properly ware-
housed.
2. Mix and/or soak lime
according to supplier’s
recommendations.
3. Maintain proper temper-
ature above 55˚F prior to,
during and after plastering.
1. Use either Quick or Slow
set gauging in the proper
proportions.
2. Maintain proper temper-
ature above 55˚F prior to,
during and after plastering.
Corrective Action
No correction – remove the
plaster and replaster.
No correction – remove the
plaster and replaster.
1. No correction – remove
finish coat, correct condi-
tion of brown coat and
replaster.
2/3. No correction – remove
finish coat and replaster.
1. No correction – remove
finish, correct brown coat
condition and replaster.
2. No correction – remove
finish, spray brown coat
with water to reduce
suction and replaster.
3. No correction – remove
finish, roughen brown
coat to provide adequate
keying and replaster.
No correction – remove the
plaster and replaster.
There is no correction for
these occurrences.
There is no correction for
these occurrences.
BOND FAILURE OF BASECOAT (cont.)