STMP sodium trimetaphosphate is a white, crystalline salt used as an additive in gypsum and wallboard production. STMP sodium trimetaphosphate acts as a dispersant and a retarder, preventing the gypsum particles from clumping or settling, and slowing down the hardening process. This improves the workability and adhesion of the gypsum slurry, as well as the drying time and strength of the wallboard.