This work deals with an integrated approach to the characterisation of historical mortars. Various techniques (Optical Microscopy on thin sections, X-Ray Diffraction, FTIR Spectroscopy, Thermal Analyses, Ionic Chromatography) were utilised in order to thoroughly analyse the mortars coming from the Basilica of St. Lorenzo (Milan, Italy), on occasion of a recent conservation work. Investigations from various, complementary points of view allowed the identification of the original components of the mortars, i. e. binder and aggregate fraction, besides the nature of degradation compounds, in order to plan the best and most respectful intervention.