The Cathedral of St. Giorgio in Ragusa Ibla (Italy): a case study of the use of protective products

The Cathedral of St. Giorgio in Ragusa Ibla like the majority of historic buildings in the Ragusa area is constructed mainly from locally outcropping calcarenite belonging to the Ragusa Formation. Through the years, the cathedral has undergone diverse restoration procedures using different protective products, the nature of which was determined by means of Fourier transform infrared spectroscopy (FT-IR) and gas chromatography coupled with mass spectrometry (GC-MS). Regardless of these interventions, the materials used today are still subject to diverse forms of alterations and degradation (alveolitation, differential degradation, decohesions, chromatic alterations and the formation of biological patinas correlated to lichen activity), which cause considerable damage to the façade. In this paper, three protective products were tested on the calcarenite of the Ragusa Formation taken from a quarry: a fluorurated elastomer, a fluorurated anionic polyurethane and linseed oil. The protective efficiency was determined, after undergoing UV radiation aging by means of capillary water absorption, porosimetric and colorimetric procedures. The results highlighted a good and persistent protective capability of both the elastomer and the fluorurated polyurethane, whereas, the linseed oil not only provoked strong chromatic variations but also quickly lost its hydro-repellant capacity with aging.