Strengthening of ancient masonry constructions by means of composite materials is strongly influenced by the properties of the substrate where the reinforcement is applied. Therefore, ageing and damaging processes affecting the masonry can play an important role in the effectiveness of the reinforcement and failure behavior. Presented in this paper is the study of the bond behavior of different ancient clay bricks and masonry specimens reinforced by carbon fiber composite sheets. Obtained results of single-lap shear tests, particularly in terms of bond resistance, pull-out curve, detachment mechanism, strain and stress distributions, are discussed to show different peculiarities of the detachment process. Moreover, the fracture energy has been computed using experimental data and then compared with the expression proposed by the Italian design code.