Hydro stone, from Adelaide Moulding and CastingSupplies is a hard and strong cement with a high water absorption resistance. Hydro stone works well in plaster and most flexible moulding compounds. It also has low viscosity slurry for filling multiple moulds at one time. Another plus is that hydro stone has an extremely fine detail when duplicated.

Preparing the mix

Use potable water at temperatures between 21 and 38°C. Since variations in slurry (Hydro Stone Gypsum Cement and water mixture) temperature produce variations in setting time, it is important to keep both hydro stone gypsum cement and water in a stable temperature environment prior to use.  The higher the temperature of the slurry, the shorter the set time. Measuring

Weigh both hydro stone gypsum cement and water at the recommended use consistency for each mix (see Technical properties). The water to hydro stone gypsum cement is critical because it governs all physical properties of the final cast piece.


Sift or strew hydro stone gypsum cement into water slowly and evenly.  Do not drop handfuls of hydro stone gypsum cement directly into the water.  Allow soaking for 1 –2 minutes.  Hydro stone gypsum cement should be fully dispersed in the water prior to mixing.  Small batches require less soaking than larger batches.


Properly mixing hydro stone gypsum cement is the most important step to producing casts with maximum strength, hardness, and other important properties. Unlike other plasters and gypsum cements, hydro stone gypsum cement cannot be mixed by hand and must be mixed mechanically.  Additionally, hydro stone gypsum cement can only be mixed by a batch process, not by a continuous process mixer.


To prevent air entrainment and provide a uniform, smooth surface, careful pouring of the slurry is necessary.  Agitation of the filled mould is a further step used to prevent air at or near the surface of the cast piece.  Whenever possible, the slurry should be poured carefully in the deepest area first so the slurry flows evenly across the surface of the mould.  Pouring a large amount of slurry directly on the face of the mould may result in slight densification of the cast at the point where the slurry strikes the surface of the mould.


All casts should be dried as quickly as is safely possible after manufacture so that maximum physical properties can develop. The best drying rooms or ovens provide

(1) Uniform and rapid circulation 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 room or oven inhibits the efficiency of the drying because the air pulled into the room is incapable of picking up much moisture from the cast piece.


Keep in a dry, stable environment indoors. Do not stack more than two pallets high. Keep away from drafts and remember to rotate the stock.