In situ application of alginate hydrogels containing oxidant or natural biocides on Fortunato Depero's mosaic (Rome, Italy)

Stone monuments in outdoor environments are subjected to biodeterioration due to the growth on their surfaces of biofilms responsible of aesthetic, physical and chemical damages. In recent years, the encapsulation of antimicrobial agents into inert matrices has aroused considerable interest thanks to the drastic reduction of the biocide amount needed to counteract the growth of biopatinas. In this study, two biocidal hydrogels containing thyme essential oil (thyme EO) or sodium dichloroisocyanurate (NaDCC), previously tested in the laboratory, were applied on three selected areas of the Depero’s mosaic located in the EUR district of Rome (Italy). A simple method to prepare the biocidal hydrogels directly in situ and their easy application on large and vertical surfaces were developed. Before and after the treatment, photographic, colorimetric, and microscopic analyses were performed to highlight the hydrogels’ biocidal effectiveness in removing all colonizers. Only one treatment was enough to completely remove the microbial patina constituted of various prokaryotic and eukaryotic microorganisms.