A system for conveying gypsum slabs through a slab sorting section, a slab distributing section, a slab drying section and a slab removal section in that order. In the sorting section, suction boxes located above the slab path support the moving slabs, which are moved by rotating rollers acting on the upper surfaces of the slabs and holding the slabs a slight distance below the openings in the suction boxes. Undesired slabs are dropped out by reducing the suction pressure. The distributing section uses a laterally-movable distributing table, suction boxes above the slabs, and blower boxes below the slabs, so that the slabs can be gently dropped into different lateral positions on the distributing table; rollers like those in the sorting section are used to control slab advance. In the drying section, blower boxes are used below the slabs for support and drying; blower boxes may also be used above the slabs in the drying section, and brush-type rollers used to advance the slabs. The drying-section boxes are preferably wedge-shaped, with air supplied from the wider edges. The supply of air to the blower and suction boxes can be selectively turned on and off as the slabs progress along their path.