The characterization of mortar properties can be accomplished by the use of thermal analysis. DTA can be used to identify various component materials and observe the reactions associated with controlled heating of the mortar, This method reveals thermal transformations, which include dehydration, dehydroxylation, oxidation and decomposition. In addition, crystalline transitions can be observed, which are exothermic or endothermic in nature. With TGA, thermogravimetric analysis, the mass of the sample is monitored (weight loss) as a function of temperature. Weight losses at reaction temperatures near 750 degrees C, indicate loss of CO2 not from pure CaCO3, but from recarbonated lime. The dehydroxylated clays acted as a "pozzolan" which imparts early strength to the mortar. However, a more complex phenomenon occurs in crushed brick mortar, since compounds of hydraulic type occur at the brick matrix interface also. The DTA and TG-DTG analyses identify the dehydration of calcium alumine-silicate phases, giving clear evidence of a cementitious mortar rather than one of pure lime. In the present work a spectrum of thermal and XRD analysis results from ancient, Byzantine, post-Byzantine and later historic mortars from Greece is presented and the relevant information concerning the characterization of traditional mortars is validated. Generally, the CO2 bound to carbonates and the water bound to hydraulic components (in weight loss%) discern two groups of mortars, the typical lime and the hydraulic, respectively. The specific classification of mortars into groups with characteristic transformations indicated by weight loss against temperature, enables discernment of : typical lime, cementitious, with crushed brick, with portlandite, with gypsum, with modern cement or of hot lime technology, mortars. Mineralogical, microstructural, mechanical and technological data could provide further evaluation criteria.