Assessing preventive surface treatments against microalgae on marble for sustainable building conservation

Abstract In this research, the effectiveness of different eco-treatments for preventing the colonisation of microalgae on marble surfaces was studied. To achieve this goal, different types of samples were employed: a fragment detached from the Lastra family mausoleum (which was constructed entirely of marble material and presents a green biofilm on its surface), old dirty marble samples, old marble samples that were cleaned and commercial new marble. A biofilm sample of this mausoleum was collected, taxonomically determined and later used in laboratory experiments as an inoculum. The surface samples were treated using a water-based solution with surfactants with and without 1% thymol. The samples inoculated with the algal community were incubated under environmental photoperiod and temperature conditions for 30, 60 and 120 days. For surface characterisation petrographic studies, stereoscopic microscopy, environmental scanning electron microscopy and epifluorescence microscopy were applied, and the surface contact angle, colour, specular glow and roughness were measured. Both treatments inhibited algal growth on marble surfaces, and their effectiveness was demonstrated over time. We propose that these surface treatments would be potentially useful for cleaning and preventing the phototrophic formation of biofilms on buildings to achieve sustainable building conservation.