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How to... Mix plaster and gysum cement.
Mixing Instructions
Storage: Store plaster/gypsum in a warm, dry area, raised from the floor to avoid moisture absorption. The shelf life of all plaster/gypsum is limited but that life can be extended by storing in air-tight plastic containers.
  1. Weigh proper amount of room temperature water in a clean container. (Warmer water will accelerate the setting time.)
  2. Weigh proper amount of plaster/gypsum.
  3. Sprinkle the plaster/gypsum into the water. (Never pour water into plaster/gypsum). As you near completion, small mounds of plaster will peak above the surface of the water. When all the plaster/gypsum has been added, allow the mixture to sit undisturbed while the plaster soaks up the water. (Several minutes).
  4. Manually: It is possible to get a good mix by using a spoon or wood dowel. Mix slowly and steadily from the bottom, using a side to side motion. Stirring in a circular motion will introduce undesirable air bubbles into the mix. Consistency of final mix should be that of heavy dairy cream. (The "old timers" are sometimes seen "elbow deep in plaster" literally mixing by hand. This is a very dangerous method since plaster becomes extremely hot when setting, potentially resulting in severe burns.)
    Electric Mixer: You can achieve a consistently good mix by using an electric drill with a Jiffy Mixer attachment. "Stir" at 1750 RPM while holding the Jiffy Mixer at 151/2 off vertical. This method is also quicker than the manual method discussed above.

Consistency and Setting Times
USG
Product
Recommended
Consistency*
Approximate
Setting Time
Ceramical  40 18 - 23 minutes
Duracal/Fastcast  26 25 - 35 minutes
Duramold  68 27 - 37 minutes
Hydrocal A-11  42 16 - 20 minutes
Hydrocal B-11  44 25 - 35 minutes
Hydrocal FGR 95  30 50 - 70 minutes
Hydrocal White  45 25 - 35 minutes
Hydroperm 100 12 - 19 minutes
Hydro-stone  32 17 - 20 minutes
Hydro-stone Super X  22 17 - 20 minutes
Hydro-stone TB  32 17 - 20 minutes
No. 1 Pottery  70 27 - 37 minutes
Puritan Pottery  66 27 - 37 minutes
Regular Casting  72 27 - 37 minutes
Regular Pottery  74 27 - 37 minutes
Statuary Hydrocal  40 25 - 35 minutes
Tuf-Cal - 20 Minute  50 17 - 22 minutes
Tuf-Cal - 30 Minute  50 27 - 35 minutes
Ultracal 30  38 25 - 35 minutes
White Art - 20 Minute  70 17 - 27 minutes
White Art - 30 Minute  70 27 - 37 minutes
* Parts of water by weight per 100 parts of material
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