Methyl Potassium Siliconate and Siloxane Inhibit the Formation of Multispecies Biofilms on Ceramic Roof Tiles: Efficiency and Comparison of Two Common Water Repellents

Abstract

Ceramic roof tiles are widespread marketed building materials, rapidly colonized by microorganisms that form multispecies biofilms on their surface and play crucial roles in biodeterioration processes. Coating tiles with water repellents is a pervasive industrial strategy employed to prevent liquid water penetration and slow biodeterioration. Very few studies have examined the links between the characteristics of water-repellent coatings and biofilm colonization patterns. Our work aims to compare the effects of coating tiles with two common water repellents (siliconate and siloxane) on the growth of colonizing microbes. We combined in situ exposure of tiles for over six years and macroscopic and microscopic observations with in vitro biotests, relying on the use of algal and fungal models. Our data showed that (1) tiles coated with water repellents were macroscopically less colonized by lichens (2) a significant fungal biofilm development at the microscopic scale (3) water repellents had very contrasting effects on our model strains. These data reinforce the great interest for industry to conduct more studies linking the nature of the water repellents with the composition of colonizing multispecies biofilms. The long-term objective is to improve the available water repellents and better adapt their selection to the nature of microbial colonization.

Current and future chemical treatments to fight biodeterioration of outdoor building materials and associated biofilms: Moving away from ecotoxic and towards efficient, sustainable solutions

“…• 4.1.4 Advantages and drawbacks Water-repellents reduce water availability for microorganisms, thus slowing down their growth and, in turn, the biodeterioration of building materials (Fassier, 2009;Urzì and De Leo, 2007). For example, silanes and siloxanes efficiently reduce building material colonization by photosynthetic microorganisms, such as filamentous Nostoc-like cyanobacteria (Urzì and De Leo, 2007), and Stichococcus bacillaris (Romani et al, 2021b). Potassium methyl siliconate has also shown in vitro effects on the growth of Cladosporium cladosporioides (Table 1) (Romani et al, 2021b).…”

“…For example, silanes and siloxanes efficiently reduce building material colonization by photosynthetic microorganisms, such as filamentous Nostoc-like cyanobacteria (Urzì and De Leo, 2007), and Stichococcus bacillaris (Romani et al, 2021b). Potassium methyl siliconate has also shown in vitro effects on the growth of Cladosporium cladosporioides (Table 1) (Romani et al, 2021b). Additionally, silicone-based water-repellents are insensitive to UV radiations, making them particularly stable through time (Charola, 2001;Fort González et al, 2000;Wendler, 1997).…”

“…Moreover, they do not lower the colonization of materials by "black" fungi such as Alternaria sp. or Cladosporium sp., which are the most resistant to chemical treatments (Hallmann et al, 2011;Krause et al, 2006;Romani et al, 2021b;Urzì and De Leo, 2007). Combining polysiloxane with copper nanoparticles reduces biocolonization and blackening of marble surfaces (Pinna et al, 2012).…”

“…From this precise assessment, different possible solutions can be considered and likely combined in a specific fashion for each specific case. For example, a pretreatment with water-repellent coatings helps to lower the required concentrations of various types of biocides, which is a first step in the design of more ecologically friendly solutions (Romani et al, 2021b). Also, an in-depth analysis of the microbial composition colonizing building materials is essential to select the best biocide or coating to use, thus avoiding the use of non-essential compounds and their release in the environment.…”