The behaviour of RC beams strengthened with NSM FRP bars was experimentally investigated. Eight beams were tested under four point bending. The effects of material type, epoxy properties, bar size and the number of NSM bars were studied. The tested beams were strengthened with a limited bond length in order to imitate as much as possible work-place conditions, as the grooves could only be cut up to the faces of the supporting columns with difficulty. The load capacity, deflection, mode of failure, FRP strain, concrete strain, free end slip and the transverse strain in epoxy and concrete of the tested beams were all analysed. Comparison of strengthened and control beams showed enhancement of 155.8% and 129.8% in the yielding loads, while the increase in the ultimate loads was 166.3% and 159.4% for beams strengthened with carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) respectively. The beams strengthened with CFRP bars experienced higher stiffness than the corresponding beams with GFRP bars. Epoxy properties, size and number of bars had little effect on the load capacity of the strengthened beams with failures mainly occurring either in epoxy or as a result of concrete cover separation The authors acknowledge the support provided by the Spanish Government (Ministerio de Ciencia e Innovacion), Project ref. BIA2010-20234-C03-02. The first author also acknowledges the support from the Generalitat de Catalunya for an FI pre-doctoral Grant, ref. 2011FI_B 00003