Abstract: A gypsum set accelerator for use in the production of gypsum wallboard comprises a tube or ball milled mixture of gypsum and up to 20 percent by weight of the gypsum of a synthetic water-soluble solid surfactant. A process for the manufacture of gypsum wallboard is also described comprising spreading between paper sheets an aqueous slurry of calcium sulphate hemihydrate defined above at a rate of between 0.5 and 15 kilograms per 100 square meters (1 and 30 pounds per 1000 square feet) of gypsum wallboard, and allowing the slurry to set. The accelerator has high potency and appears to provide wallboard of increased compressive strength.