No. 1 Pottery Plaster

AVAILABLE IN 5, 25, AND 50LB OPTIONS IN THE DROPDOWN

USG No. 1 Pottery Plaster is the best material available for sanitaryware and dinnerware casting.
USG No. 1 Pottery Plaster is formulated for long life and reduced breakage which leads to stronger
molds. USG No. 1 Pottery Plaster is available with or without thermal shock additive

MIXING INSTRUCTIONS

Use potable water at temperatures between 70 °F (21 °C) and 100 °F (38 °C). Because variations
in slurry (USG No. 1 Pottery Plaster and water mixture) temperature produce variations in set
time, it is important to keep both the USG No. 1 Pottery Plaster and water in a stable temperature
environment prior to use. The higher the temperature of the slurry, the shorter the set time.
Conversely, the lower the temperature of the slurry, the longer the set time.

Weigh both the USG No. 1 Pottery Plaster and the water prior to use for each mix. The water-to-
USG No. 1 Pottery Plaster ratio is critical because it governs the strength and absorptivity of
the mold.

Sift or strew USG No. 1 Pottery Plaster into the water slowly and evenly. Do not drop large amounts
of USG No. 1 Pottery Plaster directly into the water as proper soaking of the USG No. 1 Pottery
Plaster may not occur. USG No. 1 Pottery Plaster should be fully dispersed in the water prior to
mixing. Small batches require less soaking time than large batches. See USG IG503 Plaster Mixing
Procedures for specific soaking instructions.

Mixing USG No. 1 Pottery Plaster slurry is one of the most important steps in producing USG
No. 1 Pottery Plaster molds with maximum strength, absorption, hardness and other important
properties.

Mechanically mixed slurries develop uniform molds with optimal strengths. USG No. 1 Pottery
Plaster can be mechanically mixed through both batch and continuous processes. Proper blade
and bucket dimensions are important for obtaining the best batch mix (see USG IG503 Plaster
Mixing Procedures for details).

Longer mixing times result in higher mold strength and shorter set times.

POURING

To prevent air entrainment and provide a uniform, smooth surface, careful pouring of USG No. 1
Pottery Plaster slurry is necessary. Agitation/vibration of the filled mold is a further step used to
prevent air at or near the mold surface. Whenever possible, USG No. 1 Pottery Plaster slurry should
be poured carefully in the deepest area so that the slurry flows evenly across the surface of the
case mold.

Pouring a large amount of slurry directly on the face of the case mold may result in slight
densification of the USG No. 1 Pottery Plaster mold at the point where it strikes the surface of the
case. This produces a hard spot, giving uneven absorption.

DRYING

All pottery molds should be dried as quickly as is safely possible after manufacture so that
maximum physical properties can develop. Dry to a constant weight.

The best drying rooms or ovens provide 1) uniform and rapid circulation (minimum of 15-30 fps
(4.6-9.1 mps)) of air with no “dead spots” having little or no air movement, 2) equal temperatures
throughout the entire area, and 3) provisions for exhausting a portion of the air while replacing
it with fresh air. High humidity surrounding the drying room or oven inhibits drying efficiency
because the air pulled into the room is incapable of picking up much moisture from the molds.

The maximum temperature at which USG No. 1 Pottery Plaster molds are safe from calcination is
120 °F (49 °C). With substantial free water in the mold, a higher drying temperature can be used
without difficulty. As drying progresses, the temperature must be reduced to prevent calcination.
Before removing molds from the dryer, the temperature should approach that of the area around
the dryer to prevent thermal shock. See IG502 Drying Plaster Casts for additional information.

STORAGE AND USE

When properly used, USG No. 1 Pottery Plaster is easy to work with and complies with the federal
Labeling of Hazardous Art Materials Act, 12 U.S.C. Section 1277 and ASTM D4236. Keep indoors
at temperatures between 65 °F - 75 °F (18 °C - 24 °C) and 45% - 55% RH. Do not stack more than
two pallets high. Keep from drafts. Rotate stock. USG No. 1 Pottery Plaster should be used within
6 months of the manufacturing date located on the package. Always follow handling and use
directions and safety warnings on the package.

SDS