On-site monitoring of the performance of innovative treatments for marble conservation in architectural heritage

Innovative nanostructured treatments for stone conservation, based on dispersions of photoactive TiO2 nanoparticles, recently studied in our research group, provided interesting results after laboratory testing. Unfortunately, it is almost impossible to accurately reproduce in the lab the complexity of field exposure conditions. It is then of crucial importance to evaluate the behaviour and durability of new treatments in situ, once they are applied to real deteriorated surfaces of the architectural heritage exposed in outdoor. In the present research, the effectiveness of a TEOS-nano-TiO2 treatment and of two nanocomposites based on nano-TiO2 dispersion in organosiloxane and functionalized SiO2 for the protection of two specific marbles-Candoglia and Crevoladossola-has been evaluated on-site. The effect of the introduction of innovative titania nanoparticles in selected commercial products has been examined focusing on compatibility and protection efficacy in real exposure condition. An on-site testing protocol has been defined and carried out for 12 months after the application, considering colour and morphology changes and water absorption by capillarity. The nano-TiO2 addition does not hinder the performance of the protective treatments while it provides a positive contribution in soiling reduction. The results will be implemented in the operative framework of the ongoing conservation project of the considered historical façade. Graphical abstract Summary of the monitoring protocol of the Candoglia marble surface