Different ancient mortar samples were analyzed to characterize their binder fraction, Thermal analyses (TG. DSC) proved to be very useful in the identification of three different species of lime composed of: (a) only calcite: (b) calcite and magnesite: (c) calcite. hydromagnesite and magnesite. The hydromagnesite is well identified in the DSC curve showing the peaks corresponding to the three-step thermal decomposition. Also the same mineral was detected by FTIR and/or micro-FTIR analyses. depending on its amount in the binder fraction of the mortar. Actually the two absorption peaks characteristic of the hydromagnesite were often hidden by the wider peaks due to the asymmetric stretching of the carbonate ion, observed for the calcite and magnesite.