Bioreceptivity of sound and weathered building stones: Effects of accelerated ageing on microbial growth

The primary and secondary bioreceptivity of stone materials provide crucial insights into their susceptibility to biological colonization and biodeterioration, which is particularly relevant in the preservation of cultural heritage. This study investigates the bioreceptivity of five lithotypes (three porous limestones, a marble, and a sandstone) commonly used in both historic and modern architecture. Primary bioreceptivity, mainly influenced by the intrinsic properties of the stones, was assessed by inoculating sound (untreated) stone samples with a multi-species phototrophic culture derived from a natural biofilm and incubated under laboratory conditions for 1 month. Secondary bioreceptivity was evaluated on stone samples subjected to accelerated weathering processes, including salt crystallization, freeze-thaw cycling, and chemical attack. These accelerated ageing tests were conducted to induce controlled surface modifications (e.g., increased porosity, roughness, or microcracking) and assess the material’s susceptibility to microbial colonization under altered substrate conditions. Surface coverage areas by biofilms and chlorophyll a content were used as proxies for determining photosynthetic biomass, providing a comprehensive understanding of biofilm growth. The results from the sound and weathered stone surfaces showed a strong correlation between the degree of microbial colonization and stone properties such as porosity and surface roughness, with limestone lithotypes exhibiting the highest bioreceptivity. Weathering processes contributed notably to secondary bioreceptivity, with salt crystallization increasing biofilm development, while freeze-thaw cycling reduced biofilm growth. The novelty of this study lies in evaluating how accelerated weathering tests alter stone bioreceptivity, revealing significant implications for cultural heritage conservation strategies under changing environmental conditions. • Laboratory-based assessment of primary and secondary bioreceptivity of limestone, sandstone, and marble. • Porous limestones exhibit higher primary bioreceptivity due to their high porosity and surface roughness. • Porosity and roughness are primary drivers of bioreceptivity. • Salt crystallization and chemical attack enhance secondary bioreceptivity. • Freeze-thaw cycling reduces bioreceptivity by creating fissures less favorable to biofilm growth.