Installation Guide

12
Condition
Finish Coat
Works Hard
Slow Plaster Sets –
Not Set After Five Or
Six Hours
Plaster Sets Too Quickly
To Be Darbied Or Sets
In Mortar Box Or On
The Board
Plaster Works Hard Or
Short, Will Not Spread,
Will Not Carry Proper
Amount Of Aggregate
Construction
Gypsum finish over
basecoat.
Basecoat plaster over any
substrate.
Basecoat plaster over any
substrate.
Basecoat plaster over any
substrate.
Probable Cause
1. Basecoat plaster too dry.
2. Finish coat mixed too
stiff.
1. Retarding action of
aggregate.
2. Retarding action of water
being used.
3. Old plaster set lengthened
due to aging.
1. Tools and mixing equip-
ment not free of set plaster.
2. Dirty or contaminated
sand or water.
3. Plaster too old or became
wet in storage or on the
job site.
4. Plaster being mixed too
long.
1. Plaster is old or stored
under poor conditions.
2. Too much or improper
aggregate being used.
Preventive Action
Follow good plastering
practices.
Use only proper plaster
aggregate, potable water
and fresh plaster.
Keep tools and mixing
equipment clean, use only
potable water and clean
sand for mixing. Use fresh
plaster which has been
stored properly. Follow
good plastering practices.
Use only fresh, properly
stored plaster.
Corrective Action
1. Apply finish coat over
green base or spray the
dry base lightly with
water before finishing.
2. Use correct amount of water
when mixing finish coat.
1/2. Obtain good sand
and water or accelerate
mixes.
3. Replace with fresh plaster
or accelerate mixes.
1–3. Judiciously use retarder
to slow setting, clean
equipment and obtain
clean water and sand.
4. Reduce plaster mixing
time.
1. Blend equal parts of
fresh and old plaster.
2. Use proper aggregate at
proper proportions.
FINISH COAT PROBLEMS (cont.)
WORKING QUALITIES AND SETTING ACTION
Painting Plaster
Various job conditions such as suction differences, wet or only partially
dry walls, and reactions between paint and lime may cause unsatisfactory
paint finishes, particularly on new construction.
Alkali-resistant primers specifically formulated for use over new plaster will
permit decorating with oil or latex type paints.
Quality paint products should be used and manufacturers’ recommendations
followed. Finished plaster should be painted or covered to conceal possible
discoloration. The paint system should be suitable for use over plaster
surfaces that contain lime.
It is essential that plaster be sound and completely dry before painting.
Conventional plaster may require 30 to 60 days to fully dry.