Durability to simulated bird guano of nano-filled oleo/hydrophobic coatings for the protection of stone materials

The conservation and protection of ancient buildings and art-works made of stone materials, that constitute the Cultural Heritage of each Country, are very delicate tasks involving different experts and disciplines. The most common and successful method for protecting the stone-made constructions and art-works consists in applying on their surfaces protective layers of polymers having oleo-hydrophobic character. Polymer materials themselves can undergo degradation if they interact with external agents, thus reducing their protective features. The durability of the protected stones is the subject of many investigations in the last decades, but, among the agents able to severely affect the treated stone substrates outdoor exposed, only little attention has been paid so far to the effects of bird droppings, also known as guano. This work would contribute to fill this gap, assessing the effects due to bird excreta on two kinds of stone (a very porous, Lecce stone, and a more compact, Trani stone) protected with an experimental polymer coating containing SiO2 nanoparticles in comparison with two commercial protective polymer products. Color, surface hydrophobicity, water vapor permeability, and capillary water absorption were evaluated before and after exposure to pancreatin, used to simulate bird droppings. Different behaviors were observed depending on the stone porosity and the nature of the polymer coating. Good performance was obtained using the coatings with nanoparticles