SILICA THIN FILM SYNTHETIZED BY SOL-GEL PROCESS FOR THE PROTECTION OF OUTDOOR ARTISTIC CERAMIC IN ARCHITECTURE

A coating treatment with a silica thin film synthesized by sol-gel process was performed during the restoration of the Gio Ponti’s Church of Santa Maria Annunciata in Milan (Italy). Despite its recent construction (1964-67) the external façades made of porcelain stoneware tiles presented degradation phenomena caused either by exposure to weathering and by the fabrication characteristics of the material. A careful analysis of the deterioration of ceramic elements by optical microscopy and ESEM-EDS was performed in order to characterize the material and to project a proper intervention. A silica thin protective film was synthesized by sol-gel process, according to the method developed by the research group of Chemistry for Cultural Heritage of the University of Padua, and adapted to the specific application by the spin-off company Siltea srl. The method involves the neutral pH catalysis of the sol and the room temperature condensation of the film. The coating was applied by means of conventional air-spray gun. Optical microscopy and ESEM-EDS analysis before and after accelerated ageing on several samples were performed to evaluate the protective efficiency of the coating. The treatment was realized on a surface of 300 square meters with good results, encouraging the application of this new technology as an efficient alternative to the traditional methods, often based on the use of synthetic organicpolymers.