Reconsideration of a theory of the setting of gypsum plaster

The rates of hydration of eight samples of calcium sulphate hemihydrate, six of which were commercial calcined gypsum, were determined from the accompanying increases in temperature. The compositions of the samples and the areas of their surfaces were determined, and the sizes of the microcrystals in the hydrated and hardened systems were studied. The results strongly support the applicability of a theory of hydration of calcium sulphate hemihydrate developed earlier. The possibilities of calculating periods of induction are described, and some of the implications of the theory discussed.