Set Retarders & Accelerators
Tune the hydration window between hemihydrate slurry and the cut-off knife.
Control over the calcium sulfate hemihydrate to dihydrate reaction is the single largest lever in board-line stability. Our retarder and accelerator families let you place the initial set precisely between forming and the knife, regardless of stucco source, water hardness, or seasonal temperature drift.
Retarders work by either complexing calcium ions in solution (citric acid, tartaric acid, sodium gluconate) or by adsorbing onto growing dihydrate crystal faces (hydrolyzed keratin and collagen proteins, the BMA/Retardan family). Accelerators are typically finely ground gypsum seed combined with potassium sulfate, which lowers the dihydrate solubility curve and shortens the induction period.
On a continuous board line, a 30-second shift in the initial set time translates directly into edge cracking, sticking at the knife, or kiln entry while still soft. Choice of retarder chemistry must match the calcination route: ball mill kettle stucco tolerates protein retarders well, while flash-calcined stucco usually responds better to organic acids.