This invention relates to the use, in a foamy aqueous suspension of calcium sulfate hemihydrate, as an agent having the dual function of being a dispersing agent and an anti-defoaming agent, of a comb polymer made up of (meth)acrylic acid, a monomer which is an alcoxy- or hydroxy-polyalkylene glycol, and an ester of (meth)acrylic acid. It also relates to the aqueous suspensions thereby formed, and the plasterboard manufactured from 2 sheets of paper containing a body resulting from the drying of said suspensions.