FILM DI SILICE SOL-GEL PER LA PROTEZIONE DELLA CERAMICA NELL'ARCHITETTURA DI GIO' PONTI A MILANO

The church of Santa Maria Annunciata at San Carlo Borromeo Hospital in Milan is a prime example of contemporary architecture. The church was built between 1964 and 1967 by Gio Ponti (1891-1979), one of the main protagonists of XX Century Italian architecture. The unconventional choice of materials and shapes is the result of the architect's specific intent so their preservation is an important task in the conservation planning. The restoration project, through a careful analysis of the exterior facades degradation, highlighted a complex situation connected to contemporary art. The processes of surface alteration, synergistically caused by exposure to weathering, compositional aspects, constructive and material characteristics, show phenomena that cannot be found in historical buildings [1]. Particular attention was devoted to the external ceramic facing, made of glazed porcelain stoneware (or grès) tiles. The critical conservation status of the ceramic elements required an intervention for the consolidation of diffuse micro-cracking in the glassy coating and the protection of the still intact material. Silica thin films synthesized by sol-gel process, according to the technology developed by the Chemistry for Cultural Heritage research group (Department of Chemical Sciences, University of Padova), was used to perform an innovative protective treatment. This method involves a new synthetic path to obtain highly pure glassy silica thin films operating at low temperatures and in a neutral environment. The deposition of films is performed closely to neutral pH conditions, in order to avoid degradation of objects sensitive to acidic or basic environment. The slow drying process carried out at ambient temperature does not require the heat treatments necessary for the traditional sol-gel method and thus avoids possible damages to the substrate [2]. Phenomena involved in weathering, as well as chemical and morphological characteristics of the ceramic materials, were analysed and considered in planning the protective treatment. Compatibility with the glass substrate, stability to solar radiation, chemical corrosion and biological degradation resistance, durability and inalterability of the optical characteristics of the material are all features in accordance with the restoration needs. The encouraging results obtained show that this new technology can be widely used as an effective alternative to traditional methods, often based on the use of synthetic organic polymers.