On the basis of experimentally established data on the size and shape of gypsum crystals which constitute the solid phase in hardened suspensions of CaSO4 . 0.5 H2O, and on that of the size of pores in the materials it was shown that the strength of hardened gypsum was proportional to the area of mutual contacts between the gypsum crystals. Mechanical failure occurs at these contacts which represent the points with weakest bonds. Analyses of the microstructure of fracture surfaces resulted in the same conclusions.
