Contact Angle Measurements to Investigate Subaerial Biofilms/Porous Substrates Systems in Built Heritage Research

A sound assessment of water-related properties of porous heritage materials in the presence of subaerial biofilms (SABs) offers valuable insights into the interactions between SABs and the substrate, with significant implications for treatment strategies. However, the complexity of the SAB/substrate system is also linked to the ability of SABs to modify their composition and community organization over time in response to environmental changes. This adaptability can potentially lead to transitions between bioprotective, neutral, and biodeteriorative behaviours. Water contact angle (WCA) measurements have been used to assess the impact of SABs on surface wettability and water absorption of porous substrates. In addition, they provide a powerful tool for investigating these behavioural shifts. In this study WCA measurements were employed to characterize two model SABs systems grown on limestone specimens under controlled laboratory conditions. Experiments were performed under two relative humidity regimes to simulate different exposure conditions, with measurements taken after equilibration. The results highlighted the potential of WCA measurements in probing SAB/substrate interaction and demonstrated their effectiveness in tracking environmentally induced changes in SAB behaviour.