The invention relates to the manufacture of a reinforced slab-shaped building element (E) having a length (L), a width (W) and a thickness, said slab-shaped building element (E) comprising an upper concrete plate anchored to a lower concrete plate with a top surface and a bottom surface, said upper concrete plate being cast from relatively higher strength concrete laid out upon said top surface, said lower concrete plate being of a less strong concrete, said lower concrete plate including a base contiguous with a plurality of raised portions integral therewith, said raised portions being spaced apart in the direction of said length (L) and said width (W), said plurality of raised portions defining between them a network of recesses, at least some of said recesses including reinforcing bars (R), said raised portions and said recesses together defining said top surface.