Damage that occurs in reinforced concrete elements can reduce the capacity and serviceability of these elements. One of the damages that may be encountered is spalling or delamination of concrete covers. Repairs to this type of damage can be carried out by patching methods. This research uses unsaturated polyester resin mortar (UPR-mortar) as a patch repair material to recover the damage of two-way slabs. Laboratory investigations were carried out to determine the effects of variations in patching location and loading on the ultimate capacity. The development of crack patterns as the load increases, the final yield lines formed at the time of collapse, and the magnitude of the ultimate load are the main data discussed in this research. In addition, load-deflection behavior, stiffness and toughness are also presented and discussed. Yield Line Theory (YLT) has been applied using virtual work principle with several assumptions and simplifications to estimate the ultimate load of the slabs. The experimental results show that UPR-mortar is able to recover the capacity and stiffness of the damaged slab, but it can not restore the toughness to the original level. The theoretical strength of the patched repair slabs estimated by simplified YLT shows that it is at least 90 % compared to experimental results.