Preserving the contemporary mural “Musica Popolare” by Orticanoodles in Milan, Italy: Deterioration processes and protection performance of commercial coatings

• Six commercial coatings were applied on a real street artwork and monitored over 1-year of natural ageing. • In-situ testing protocol was set up for assessing protection efficacy and durability. • Acrylic-based coatings in sheltered areas showed adhesion issues and a tendency to attract PM. • None of the commercial coatings offered optimal protection after 1-year. This study aims to investigate the possibility of protecting real street artworks in urban outdoor conditions. Specifically, this paper focuses on a testing experimental work carried out on the mural “Musica Popolare” (2016) in Milan by Orticanoodles and includes: i ) the assessment of the state of conservation through in-situ and micro-invasive techniques; ii ) the set-up of an in-situ testing protocol to assess the compatibility and efficacy of protective treatments; iii ) the one-year monitoring testing campaign. This study investigates the deterioration processes of the paint and evaluates the protective performances of various commercial coatings, which were previously tested under laboratory conditions. Notably, the mural experiences three distinct exposure conditions (fully exposed, partially exposed, and sheltered) allowing for a comparative evaluation of their effects. The coatings performance was evaluated by using a testing protocol including: portable digital microscopy, VIS reflectance spectroscopy, glossmetry, and vertical water contact angle measurements. After one year of natural ageing, the monitoring results indicate that acrylic-based coatings offered only limited protective action of the painted surface, ensuring a moderate colour retention but an insufficient protection towards liquid water. In sheltered areas, the application of protective coatings had a negative effect, making the treated surfaces more unstable than the original paintings without significantly improving water repellency (WCAs). An increase of particulate matter (PM) adhesion to the surfaces was also observed. Contact angle measurements indicated that only the fluorinated coatings achieved and maintained good water repellency over the one-year period. However, none of the tested coatings provided satisfactory protection over the monitoring period, highlighting the need for more innovative and effective preservation strategies for these artworks.