The dewatering channel beneath the recesses (1-12) works in conjunction with an outlet (27) which exits on the plate underside. At its deepest point the channel runs along the bending line of the loaded plate and transversally to the recesses (1-12), whilst the outlet issue in the dewatering channel, or communicates with it through the plate concrete. The dewatering channel issues on the counterposed longer basic plan edges of the rectangular basic form of the plate (16) and is cylindrical. It is arranged orthogonally to the recesses (1-12) spaced apart and running parallel to one another. For prodn. of the outlet, the hole is made (29) vertically through the plate. ADVANTAGE - To obviate building damage caused by accumulated water in hollow ceiling plates.