Processes in the Setting of Plaster

CaSOj 2H2O — -H2O CaS04 All CaSOa A 111 — — C aS04 2H2O 

The plaster powder should be suspended as homogeneously as possible when making a slurry of plaster in water to avoid settling. This ensures thorough wetting of the individual plaster particles and the dissolution of the outermost layers of the hydrated hemihydrate (or anhydrite) particles. 

After this so-called induction period , dihydrate crystals from the supersaturated solution start to nucleate round the particles. Further growth of the needle-shaped dihydrate crystals follows which, for the correct ratio of water to plaster, mat to a clo.se-grained. structure in which not yet 

After the induction period (initial solution of hemihydrate t r anhydrite), nuclcation of dihydrale occurs. Further crystal growth leads to a close-grained structure of dihydratc crystals which accounts for the rigidity of plaster Excess water is rcmove .l by drying 

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