The marly limestone, a difficult material to restore: the case of the San Fruttuoso di Capodimonte Abbey (Genoa, Italy)

The on-site assessment of the effectiveness and durability of conservation treatments have several drawbacks which have their origin in the demands of the owners (both from the aesthetical point of view and with the need to conclude the restoration as soon as possible), and in the requirements of the restorer related with the logistic of the yard and with the need to satisfy the owner demands. These aspects are often in conflict with the methodological approach used in the scientific framework for evaluate the performance of applied treatments. The aims of this paper is to suggest practical solutions, capable to overcome the previous problems in the assessment of the efficiency of the consolidating and protective treatments applied on the marly limestone ashlars of the Abbey of San Fruttuoso di Capodimonte (Genoa, Italy). The abbey is located at the bottom of a bay few meters from the see, therefore strongly exposed to the action of the marine aerosol and wave erosion. The consolidation and protection of the marly limestone building material was performed by testing several products both inorganic and organic. Preliminary tests were performed on laboratory samples. Afterward the same products were applied on selected ashlars of the façade in order to study their performance in a real condition. The products were ethyl silicate, ethyl silicate with polysiloxane, litium silicate, nanosilica, ammonium oxalate, ammonium phosphate, silane/siloxane, fluorelastomers and acrylic polymers and acrylic/siloxane. The study of the effect of the treatments on the stone samples was performed by non-destructive and micro-destructive methods, and an assessment procedure has been proposed.