A process for stabilizing plaster includes: a) providing a heated HH-plaster; b) feeding the hot plaster in a moistening device having walls heated to at least 100.degree. C.; c) injecting water and/or steam into the moistening device in conditions that such not yet moistened surfaces of the plaster are exposed to the injected water and/or steam; d) maintaining an atmosphere in the moistening device at a level of the dew point in the range of 75 to 99.degree. C.; e) feeding the moistened blend into a curing device; f) maintaining an atmosphere in the curing device above 75.degree. C. for at least 3 minutes; g) feeding the moistened and cured blend into a drying device; and h) drying the moistened and cured blend.Also an apparatus for moistening .beta.-hemihydrate plaster includes a rotating drum with lifting blades inside where all walls in contact with the product are externally heated at a temperature above 100.degree. C.