Relationship between certain ceramic roofing tile characteristics and biodeterioration

This paper examines the relationship of certain red ceramic roofing tile properties to roofing tile biodeterioration. The following properties were studied: apparent porosity, roughness, and the presence or absence of two types of coatings.The effect of apparent porosity was studied by varying the peak firing temperature of a standard industrial red ceramic roofing tile composition and by preparing several clay mixtures, of different chemical and mineralogical composition, that were fired at various peak temperatures. The effect of roofing tile roughness was determined by either polishing or sanding fired standard red roofing tiles. A waterproof ceramic glaze coating and a photocatalytic coating were formulated to analyse the effect of the presence of different types of coatings. Roofing tile bioreceptivity was evaluated with a method developed in a previous study using the cyanobacteria Oscillatoria sp, which enabled roofing tile resistance to microbial colonization to be determined.As expected, bioreceptivity rose as apparent porosity (measured as water absorption) increased, enabling possible water retention, which favours biological growth. Similarly, greater roughness encouraged micro-organism adhesion and raised bioreceptivity. It was found that, after prolonged exposure periods (several months) under very favourable conditions for biological colonization, roofing tiles coated with the waterproof ceramic glaze were colonized. However, glazed standard red roofing tiles covered with a TiO₂ photocatalytic coating exhibited practically no biological growth under the test conditions used, even after long exposure times, owing to the chemical-physical effect of the TiO₂-based coating.