Treatments with self-cleaning products for the maintenance and conservation of stone surfaces.

Cleaning stone surfaces is a crucial issue as irreversible and potentially harmful for the stone itself. Inadequate interventions might cause damage also visible over the time. Moreover they often have to be repeated, especially in urban areas, where the surfaces are more subjected to dusts deposition and pollution alterations. In order to reduce the need for cleaning, TiO2 -based treatments have been proposed for their self-cleaning, depollution and antibacterial properties. These products are currently used to coat the outdoor surfaces of buildings but little experience has so far been made in the field of Cultural Heritage. This paper concerns the experiments carried out to evaluate efficiency, durability and harmfulness of three different TiO2 -based products, either in form of nanoparticles or mixed with hydrophobic polymers, used to treat three carbonatic stones. A polydimethylsiloxane as reference polymer was used. Specimens of these stones were exposed to an urban polluted outdoor environment for eight months. The specimens were investigated by colorimetric measurements, surface observations and X-ray microanalyses by electron microscopy, contact angle measurements, Rhodamine tests, ion chromatography measurements and elemental analyses by X-ray fluorescence. The results showed that the photocatalytic products have a mild self-cleaning effect depending on the stone and tend to be easily washed away by the rain. Keywords: