A multi-analytical approach for the study of hydrofobizing coating for cultural heritage

The deterioration process of stone monuments includes the combined action of physical, chemical and biological factors, which induce severe modifications on the surface and structural integrity of the materials [1]. The most appropriate way to avoid deterioration is to prevent water penetration into the stone bulk, since accumulation of water is mainly responsible for stone decay. Different kinds of materials have been used up to now as protective hydrophobic coatings on architectural surfaces. In this study we have treated stones commonly employed during centuries (Carrara, Candoglia and Botticino marbles and Angera Stones) with different commercial water-repellent protective agents (siloxanes). A multi-analytical protocol has been set up in order to test the different coating performances. In this regard the protected surfaces have been characterized by several techniques, such as XRD, SEM-EDS, FTIR, TGA, IC, XPS, AFM, water absorption by capillary, CIE-Lab colorimetric analyses, contact angle measurements and surface energy elaborations. In order to investigate the stability of the coatings both accelerated aging tests by UV irradiation (500W, 250-315 nm) and prolonged exposure in a typical urban polluted environment were carried out. Colorimetric measurements (CIELab) were performed to verify the color modification (yellowing) of the protective film due to solar exposition. Not significant variations ( i.e. ΔE* < 5) were registered. The effectiveness of the different tested coatings in reducing water absorption and salts formation has been also demonstrated.