![]() The maximum temperature at which plaster casts are safe from calcination is 120 ☏ (49 ☌).With substantial free water in theĬast piece, higher drying temperatures can be used without difficulty.As drying progresses, the temperature must be reduced to prevent calcination.The safe drying zone is in the shaded area of graph (below, right). High humidity surrounding the drying room or oven inhibits the efficiency of the dryingīecause the air pulled into the room is incapable of picking up much moisture from the molds. Of the air while replacing it with fresh air. ![]() Having little or no air movement, (2) equal temperatures throughout the entire area, and (3) provisions for exhausting a portion The best drying rooms or ovens provide (1) uniform and rapid circulation (minimum of 15-30 fps) of air with no “dead spots” ![]() Where the slurry strikes the surface of the mold.ĭrying All plaster casts should be dried as quickly as is safely possible after manufacture so that maximum physical properties can develop. Pouring a large amount of slurry directly on the face of the mold may result in slight densification of the cast at the point Whenever possible, the slurry should be poured carefully in the deepest area so the slurry flows evenly across the surface of the mold. Agitation of the filled mold is a further step used to prevent air at or near the surface of the cast piece. Pouring To prevent air entrainment and provide a uniform, smooth surface, careful pouring of the slurry is necessary. Longer mixing times result in higher cast strength and shorter setting times. Proper blade and bucket dimensions are important for obtaining the best batch mix (see IG503 for details). Plasters can be mechanically mixed through both batch and continuous processes. Mechanically mixed plasters develop uniform casts with optimal strengths. Hardness, and other important properties. Mixing Mixing the plaster slurry is one of the most important steps in producing plaster casts with maximum strength, See bulletin IG503 for specific soaking instructions. Small batches require less soaking than large batches. The plaster should be fully dispersed in the water prior to mixing. ![]() Do not drop handfuls of plaster directly into the water. Soaking Sift or strew the plaster into water slowly and evenly. The water-to-plaster ratio is critical because it governs the strength Measuring Weigh both the casting plaster and water for each mix. The higher the temperature of the water, the shorter the set time. Since variations in slurry (the casting plaster and water mixture) temperature produce variations in setting time, it is important to keep both the plaster and water in a stable temperature environment prior to use. Preparing the Mix Use potable water at temperatures between 70 and 100 ☏ (21 and 38 ☌). ![]() Compressive Strength 1,200 psi 8.27 MN/m2ĭry Compressive Strength 2,400 psi 16.55 MN/m2 Use Consistency (parts of water by weight per 100 parts casting plaster) 65 65ġ Hr. #1 CASTING PLASTER is similar to white art plaster, except mixed at a lower use consistency to increase strength, chip-resistant, and to further minimize paint absorption. Hard working surface with reduced paint absorption. Industry standard for figurines, plaques and lamp bases. ![]()
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