The water-reducing agent is an additive that can keep the working fluidity of gypsum slurry unchanged and significantly reduce the added amount. Adding water reducing agent in the production of gypsum board, even in the case of a lower water-to-slurry ratio, still can improve the proper fluidity of gypsum slurry. Therefore, reducing the amount of process forming water added. During gypsum board drying, the amount of evaporated water is correspondingly reduced, reducing the energy consumption of drying gypsum board and the production cost.

Water reducing agents are mostly surface-active substances. Anionic water reducers include sodium naphthalene sulfonate formaldehyde condensate salts.

Sodium naphthalene sulfonate formaldehyde water reducing agent is a slightly yellow powder, easily soluble in water. It is prepared by sulfonating naphthalene and condensing it with formaldehyde, and then neutralizing it. It has a good water-reducing and strengthening effect on gypsum slurry.

Sodium naphthalene sulfonate formaldehyde water-reducing agent, the amount added to the plasterboard slurry is about 0.2% of the mass of plaster, reducing the amount of water added by 5%~10% and increase the strength of gypsum board by 5%~ 10%.