Isotopic analysis for degradation diagnosis of calcite matrix in mortar

Mortar that was used in building as well as in conservation and restoration works of wall paintings have been analysed isotopically (?13C and ?18O) in order to evaluate the setting environments and secondary processes, to distinguish the structural components used and to determine the exact causes that incurred the degradation phenomena. The material undergoes weathering and decay on a large proportion of its surface and in depth, due to the infiltration of water through the structural blocks. Mineralogical analysis indicated signs of sulphation and dissolution/ recrystallisation processes taking place on the material, whereas stable isotopes provided information relative to the origin of the CO2 and water during calcite formation and degradation processes. Isotopic change of the initial ?13C and ?18O in carbonate matrix was caused by alteration of the primary source of CO2 and H2O in mortar over time, particularly by recrystallisation of calcite with porewater, evaporated or re-condensed water, and CO2 from various sources of atmospheric and biogenic origin. Human influence (surface treatment) and biological growth (e.g. fungus) are major exogenic processes which may alter ?18O and ?13C in lime mortar.