Superhydrophobic films for the protection of outdoor cultural heritage assets

A very simple method that can be used to impart superhydrophobicity to stone surfaces of monuments using common and low-cost materials that are already employed or are easy to be found by conservators is presented. A siloxane-nanoparticle dispersion is sprayed on a stone, and this process can result in the formation of a rough two-length-scale hierarchical structure that exhibits water repellent properties, provided that the nanoparticle concentration in the dispersion is higher than a critical value. Superhydrophobicity (static contact angle >150° and contact angle hysteresis