Abstract: An apparatus for use in the manufacture of plasterboard (100) having at least a first side faced with a facing liner (2), a cementitious core (1) and an opposite side faced with a backing liner (4), includes a support surface (3) with a required surface finish to support the facing liner (2) and the first side of the plasterboard, pressurized fluid supply means to supply a fluid at above atmospheric pressure and at least one fluid directing means (5) to direct the pressurized fluid from the pressurized fluid supply means onto the opposite side of the plasterboard after the cementitious core (1) has partially set but before it has set to a knife set point. The pressurized fluid exerts a substantially uniform pressure on the backing liner (4) and the opposite side of the plasterboard, thereby smoothing the facing liner (2) and the first side of said plasterboard by urging them toward the support surface (3).