A gypsum slurry includes calcium sulfate hemihydrate, water and calcium sulfate dihydrate, where the calcium sulfate dihydrate is added downstream of the mixer. In an optional embodiment, the a gypsum slurry includes calcium sulfate hemihydrate, a polycarboxylate dispersant, water and coated calcium sulfate dihydrate. In this case, the hydrophilic, dispersible coating is selected to serve as a modifier to enhance the ability of the dispersant to fluidize the gypsum slurry.