Transparent stable coating materials for stone protection

Conservation of historical buildings is an important issue and the environmental conditions seriously affect the monumental stones. The protection of cultural heritage buildings and monuments by surface treatment with polymers is a common practice due to their ability to form a protective layer on the monumental surface as well as to control the transport of different fluids from the surface to monument interior. In this work three different substrates were used: Carrara/Botticino marbles and Angera stone. Commercially available siloxanes and nano-oxides films were used as protective agents to improve the hydrophobicity features of the different tested materials. Morphological (SEM-EDS), structural (XRD, XPS), thermal (TGA) and spectroscopic (FTIR and DRS) analyses were carried out on coated and uncoated stones to establish the changes of appearance, color, and water absorption. Static/dynamic contact angle measurements and surface free energy determinations were adopted to evaluate the final wettability and after UV-light exposure and artificial ageing. In order to evaluate soluble salts formation into the stones and to test the protective action of the applied coatings, the three substrates were exposed to air in a typical polluted urban environment (Milan University Campus). The results show the effectiveness of the coating layers in reducing salts formation.