Environmental decay of ancient stucco decorations subject to outdoor exposure

Neoclassical “stucco” decorations were added in 1840 to the XIV cent. church of San Francesco in Fano (Italy) in order to decorate its interior, but, as a consequence of the roof demolition in 1930, they have been exposed to outdoor conditions for almost 80 years. In view of a possible restoration work without reconstruction of the roof, this study aims to assess the vulnerability of the stucco decorations, by characterizing the constituting materials, identifying the degradation mechanisms and evaluating the stuccoes conservation state. Firstly, an analysis of microclimatic and air quality data of the surroundings of the church was performed to evaluate the environmental aggressiveness and the possible degradation causes. Then the stuccoes were characterized in order to evaluate their articulation in multiple layers, to identify their mineralogical composition and possible presence of organic additives, to determine their pore size distribution and to assess their conservation state. In spite of their gypsum nature, the relatively good conservation state of the stuccoes seems to be ascribable to the finishing layers, realized with the addition of lime (giving calcite, less soluble than gypsum) and/or worked to reduce porosity, so that stucco decorations designed for sheltered conditions proved to be partially resistant to outdoor environment too.