The present paper summarizes the findings of an experimental programme to investigate a strengthening/repair technique through the introduction of a new RC layer to an existing slab. Six RC slabs, composed of twelve cantilever and six interior spans, were tested under monotonic transverse loading. The behaviour of statically determinate cantilever spans and indeterminate interior spans was examined by comparing the test results of these specimens to the results of reference slabs, in which the existing and additional layers were cast monolithically. The influences of recovering the permanent slab deformation before repair and the spacing of the shear connectors between the existing and additional layers were investigated. The tests indicated that recovering the permanent deformations of a slab before repair substantially reduces its rigidity while having little influence on the ultimate load. Furthermore, debonding of the reinforcement was observed to considerably decrease the load capacities and rigidities of the slabs.