Mixing
Plaster Slurry sets before
it is sufficiently soaked and completely mixed.
Cause A: Contaminated plaster
Cure A: Determine if plaster became contaminated after its removal
from bag. First mix plaster from the storage bin in one mix. Then,
under identical conditions, use plaster directly from the bag for a
second mix. Any lumps of setup plaster in bags or storage bin
should be removed. If both mixes set too fast and do not appear
contaminated, the plaster may be at fault or either of the two
following causes may be present:
Cause B: Dirty mixing equipment.
Cure B: Clean all mixing equipment to remove set plaster or other
contamination. Dirty equipment accelerates setting time.
Cause C: Impurities in mixing water.
Cure C: While this problem is extremely rare, if excessive alum,
chlorine or sulfur is present in the water, the set could be
accelerated. Check plaster by making a mix with distilled water.
Plaster should always be mixed with water fit to drink.
Plaster unusually slow in
setting.
Cause: Contamination
Cure: Confirm that plaster has not become contaminated by sugar,
glue or organic acids. If not contaminated, fault could be improper
formulation for setting time by manufacturer. Accelerate set by (1)
stirring mixture faster, (2) stirring for a longer period of time,
(3) using warm water or plaster to make the mix, or (4) using a
combination of these three changes in mixing.
Lumps ranging in size from
pellets to rocks are in plaster before mixing.
Cause A: Plaster has absorbed moisture from the air, or water has
been splashed into the bin.
Cure A: Equip plaster storage bin with tight-fitting lid and keep
it closed.
Cause B: Plaster has become wet en route to your plant.
Cure B: Bags showing evidence of water should be examined before
carrier is relieved of responsibility. Note: Paper bags are usually
wrinkled when wet, and lumps have a smooth side next to paper.
Carrier inspection should be initiated as the carrier is
responsible for this damage.
Cause C: Plaster has become wet in storage.
Cure C: Store plaster in warm, dry, ventilated place; keep off of
damp floors.
Cause D: Packing lumps in bags of plaster.
Cure D: Do not store plaster in dumps higher than ten bags. Always
rotate stocks, using older plaster first. Packing lumps usually are
the result of lengthy storage. Never use lumpy plaster.