Preserving sandstone artifacts in humid conditions: Antifungal efficiency of F-ZnO/SiO2 coatings

Sandstone buildings in humid environments are highly susceptible to fungal colonization, which poses a significant threat to the buildings’ preservation. Therefore, the development of coatings with antimicrobial properties is essential to protect these structures. This study demonstrates the antifungal activity and durability of amphiphobic and UV-absorbing F-ZnO/SiO₂ (FZS) coatings. We show that the coating efficiently inhibits the growth of Aspergillus niger, protecting the sandstone surface from one of the most common molds. A fungal inhibition rate of up to 94 % was achieved with FZS nanocomposite concentrations >0.30 % (g/L). To ensure consistent antifungal performance along with enhanced water repellency and durability under practical conditions, a concentration of 0.37 % was selected for the FZS coating. Accelerated aging tests revealed that the coated sandstone retained its antifungal activity for over 56 days under harsh environmental conditions, exhibiting an antifungal effect 800 % greater than that of uncoated sandstone. After 70 days, the coating still retained its water repellency. These results underscore the potential of the coating for long-term protection of sandstone relics, offering durability and ease of maintenance for real-world applications.