In the application of cement composites as Externally Bonded Reinforcement (EBR) for concrete structures, debonding is reported to be a common and undesired failure mode. This paper presents an indirect bond identification method that incorporates the nonlinear material behaviour of cement composites. The extended nonlinear indirect method is compared with a linear method by means of virtual and laboratory experiments. The virtual experiments allow omitting measurement scatter and hence quantify the error inherent to the theoretical assumptions. The laboratory experiments validate the use of the indirect method on real slip measurements. The results show that incorporating the cement composite’s nonlinear secant modulus as a function of the occurring strain is essential to accurately determine the cement composite – concrete bond from experiments.