Mixing The ‘Casting’ Plaster—Hydro-Stone or Hydro-Cal
How to mix plaster, using the old-fashioned landfill method. This is the easiest way to mix. The manufacturers recommend that you mix plaster by weight. For example—5 lbs water to 8 lbs. plaster. To alleviate all the measuring, the landfill method, is the easiest and nearly fail proof.
- Estimate the volume of water that you will need—approx. 2/3 the air space.
- Sift plaster into water (not the reverse).
- Keep sifting without stirring.
- Keep adding the sifted plaster until the entire surface of your container is covered with a mud-like coating. (It should look like a puddle of mud that has been drying in the sun.) This is called the landfill method.
- Let sit for a several minutes. If the landfill should sink, or not soak up all the water, add more plaster now. Do not stir until it’s ready and all the water is absorbed in the landfill, about 3 to 5 minutes. (If you’ve had to add more plaster, let the plaster sit for a few more minutes). Hint—do not get impatient.
- Now stir the mixture thoroughly without whipping it. (If you whip the plaster it will create air bubbles, which will destroy cast pieces). The mixture should be pourable – about the consistency of thick pancake batter—not thin.
- The plaster should be poured immediately after mixing.
- After the molds are poured, tap the mold to knock out air bubbles.
- As plaster cures, it becomes very hot. (Never attempt to cast body parts with plaster—you would lose them!)
- When the plaster is cool to the touch and no moisture is left, the pieces can be carefully taken out of the mold.