Abstract: A floor for buildings is disclosed. The floor comprises a prefabricated reinforced concrete slab (1) with a smooth flat top surface (15), said slab (1) having been cast upside-down in a mould with a smooth flat bottom (2). Said slab (1) is supported on a base (11) arranged beneath the slab (1) with the weight of the slab (1) uniformly distributed thereover. A method for making said floor is also disclosed.