The efficiency of a seismic retrofit using externally bonded fiber-reinforced polymer composites on existing damaged reinforced concrete joints, designed prior to the introduction of modern standard seismic design code provisions in the mid-1970s, are herein presented, based on experimental investigations on BEAM-column joint subassemblies. The experimental program comprises 8 external BEAM–column joint connection subassemblages tested in 2 phases, the first phase was the damaging phase and the second was aimed to the repairing the damaged joints. The joints had no BEAM-column joint transverse reinforcement and special stirrups in BEAM and column critical lengths. These Non-Seismically designed (NS) joints were damaged with different levels at the first phase of the experiment. In the second phase, the damaged joints were strengthened with externally bonded carbon-fibre-reinforced plastics (C-FRP) sheets. From the observed responses the load carring capacity and stiffness of the pre-damaged strengthened joints were improved in moderate initial damages (less than 1.5% drift ratio). Also, the use of CFRP sheets increased the capacity of energy dissipation of the rehabilitated BEAM–column specimens in comparison to as-built specimen. It can be deduced that the technique of externally bonded retrofitting (EBR) using C-FRP sheets is efficient in moderately pre-damaged joints, i.e. the damage levels less than 1.5% drift ratio. This level is named as the repaire-ability level by using EBR strengthening method.