The church of Santa Maria delle Grazie al Calcinaio by Francesco di Giorgio Martini. New studies on the characterisation of the facing wall decay in a striking architecture of the Italian renaissance

The study aims to document the state of conservation and to interpret the alteration processes of the facing wall on the Calcinaio church. The masonry built by ashlar is affected by severe decay phenomena, which in a few years could lead to the almost complete cancellation of the finishing traces in the surface of the ashlars and the significant loss of the architectural decoration. In this paper a specific aspect of degradation has been considered. It concerns the widespread detachment phenomena of material, thin slabs of different thicknesses, from the surface of the ashlars. It is a degradation with very peculiar characteristics, as it cannot be assimilated to the sandstones degradation processes usually taken into consideration. It is a form of degradation to be interpreted in diagnostic terms and to be understood in the operational implications regarding possible conservation interventions. The widespread traces of thin layers of lime-based mortar existing in the facade are another salient aspect, which would suggest a protective finish extended to the entire walls. If this hypothesis were confirmed, it would document a completely different original character compared to the image of the church established over time. In order to clarify the questions that raise these two issues, an articulated laboratory investigation program, still in progress, has been launched. Some first results of the research are illustrated in this contribution.