Abstract: A conveyor belt is formed with depressions which are bounded by sealing edges, and tiles corresponding to the outline of the respective depressions are continuously admitted from above onto the belt and inserted into the depressions so as to be in sealing contact with the respective sealing edges. A layer of hardenable synthetic plastic material is then deposited on the belt over the tiles so that the latter are partially embedded in and united by the layer when the same hardens, thereby obtaining a unitary structure. Subsequently this structure is subdivided in plate elements of desired size.