A gypsum board according to the invention comprises calcium sulphate dihydrate; Tartaric acid in an amount in the range of 0.01 to 0.1% w based on the weight of calcium sulphate hemihydrate; A fluidizer in an amount of 1.0 to 10.0 kg/m.sup.3; Starch in an amount of 3.0 to 12.0 kg/m.sup.3.

A gypsum hardened body including a gypsum slurry that has been hardened is provided. The gypsum slurry is obtained by mixing calcined gypsum, calcium hydrogen phosphate dihydrate, water, and foam. The specific gravity of the gypsum hardened body is greater than or equal to 0.3 and less than or equal to 0.8.

A gypsum hardened body including a gypsum slurry that has been hardened is provided. The gypsum slurry is obtained by mixing calcined gypsum, calcium hydrogen phosphate dihydrate, water, and foam. The specific gravity of the gypsum hardened body is greater than or equal to 0.3 and less than or equal to 0.8.

A fire-resistant gypsum panel comprises: a gypsum core layer comprising set gypsum and a high temperature sag-resistant material including mineral wool in an amount between 0.2% and 3.0% by weight of gypsum.

A waterproofed gypsum board and associated method are provided, featuring the use of a mixture of magnesium oxide and a gypsum crystal modifier for improving the resistance to sagging of the waterproofed gypsum board, in particular, in moist and warm climatic conditions.