Nano-TiO2 coatings for cultural heritage protection: The role of the binder on hydrophobic and self-cleaning efficacy

In this work, nano-TiO2 was combined with three different binders and applied on two stone substrates, namely the Carrara marble and the Noto calcarenite, two lithotypes extensively used in built heritage. The performance of all tested coatings was evaluated by scanning electron microscopy (SEM), roughness measurements, capillary water absorption test, static contact angle calculation, colorimetric measurements, UV aging and self-cleaning test. Results suggested the key role of interaction between coating and stone surface in terms of penetration of the product, hydrophobicity, variations of surface roughness and durability, which define the performance of the coatings. Specifically, among the three tested products, the best behaviour in terms of hydrophobicity, durability and self-cleaning properties was shown by both the acrylic (Fosbuild) and fluorinated (Akeograd P) suspensions. Conversely, the Paraloid id B72 - TiO2 mixture led to an intense superficial alteration of both stones and showed scarce water-repellent and photo-degrading effect.