The aim of the present work is to propose a new micro-mechanical deductive approach to predict effective mechanical properties of micro-cracked brick/mortar interface in masonry structures. This model, based on a previous study proposed by Rekik and Lebon (2010), represents an innovative and analytically consistent way to describe meso-scale damaging phenomenon localized at the interface between deformable solids. The focal point is to assume the existence of a new material layer between brick and mortar, called interphase. This multi-scale method combines standard homogenization technique (law of mixtures, classical bounds, numerical, random), continuum damage mechanics (CDM) and asymptotic technique in order to obtain the brick/mortar interface constitutive law. In this work it will be shown that only soft behavior interface is considered. It has been found that the variable orientation of micro-cracks induces an evolution of the material simmetry. Moreover, the angle influence on interface's stiffness appears only at higher order terms of the asymptotic expansion.