Protective effect of endolithic fungal hyphae on oolitic limestone buildings

Abstract

International audienceThis study presents characterizations of weathering forms of the same oolitic limestone from four quarries and eight monuments exposed on various environmental conditions focusing on the water-proofing effect of endolithic organic matter. Patinas were analyzed by X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDX), capillarity coefficient through weathered and unweathered sides, gypsum content and porous network morphology by epoxy resin molding. Study of weathering forms on old quarries indicates that lichens colonization (Verrucaria nigrescens and Caloplaca aurantia) can fill the superficial porous network with a dense network of lichenised fungal hyphae. Capillary coefficient measurement on natural and calcinated samples showed that endolithic organic matter can waterproof the stone and could act as a sulfate contamination barrier. Similar endolithic organic layer due to ancient lichens growth are found on some antique monuments of the Nîmes downtown and could explain their well-preserved state, unlike decayed 19th century churches that were never colonized by lichens

The Role of Fungi and Lichens in the Biodeterioration of Stone Monuments

“…Concha-Lozano et al [114], comparing samples from well preserved and deteriorated limestone monuments in Nîmes and from quarries, found that the thick network of endolithic hyphae can act as a barrier increasing waterproofing of the stone and slowing down the sulphate diffusion into the stone. These results are very promising, nevertheless a standardization of water absorption measurements in situ should be necessary as environmental humidity, and consequently water content of lichens, could entail noteworthy variation in the results.…”

Lichens as Agents of Biodeterioration

“…A protective effect by fungal hyphae for oolitic limestone buildings has also been noted (Concha-Lozano et al 2011). However, when lichens are removed by mechanical and/or chemical methods, the structural integrity of the substratum can be reduced and is thereby far more vulnerable to weathering (Silver and Wolbers 2004;Tratebas 2004;McIlroy de la Rosa et al 2012a).…”

Color thresholds for aesthetically compatible replacement of stones on monuments

“…Therefore, replacement materials have to be chosen from commercially available stones. Their required specifications are usually accurate with regard to mechanical and water transfer properties . In practice, the ranges of compatible properties values are usually defined around those of the original stone …”