In practical engineering works, external bonding (EB) of fiber reinforced polymer (FRP) composite materials to concrete cannot be as perfect as in laboratory. Defects in bonding, therefore, cannot be avoided. An experimental program including single shear pull-out tests on EB-FRP concrete joints and three-point bending tests on reinforced concrete (RC) beams with/without EB-FRP was conducted. The effects of existing cracks in concrete with different spacing and widths, as well as FRP location relative to the centerline of specimen, were studied. Most of the specimens in the experimental program were prepared by unskilled personnel to simulate the "imperfect" workmanship. Test results show that EB-FRP joints with more than 10% concrete pulled off on the bond surface could have stable strength and ductility. Transverse offset of FRP from longitudinal center line does not have a significant effect on bond behavior. Existing cracks have a two-sided effect on bond-slip relationship. Cracking of concrete causes degradation of the bond slip relationship when crack width is large. However, cracking with smaller crack width could enhance the bond behavior to a certain degree. Existing cracks have limited influence on the load-deflection curves of FRP strengthened RC beams.