Biocide-Containing Varnish for the Protection of Sandstone: Comparison of Formulations and Laboratory Test Methods

Abstract

Two formulations of acrylic varnish, with and without either of two dry film biocides--one a mixture of isothiazolinones and benzimidazole derivatives, and the other a carbamate--were tested in vitro for their activity against mixtures of filamentous fungi and cyanobacteria found on sandstone buildings. Growth on filter-paper squares coated with the varnishes was assessed semi-quantitatively by naked eye, quantitatively by image analysis and chemically by measurement of ergosterol and chlorophyll a. The lower solvent content (higher resin) varnish was more inhibitory to cyanobacteria than the higher varnish content, whilst the opposite was true for the fungal inoculum. The carbamate biocide was effective against cyanobacteria, unlike the isothiazolinone mixture, but the latter produced more inhibition of fungal growth. The three assay methods produced generally similar results, although visual observation was obviously the most imprecise. There was an anomaly in the ergosterol measurements, which was considered to be caused by the varying ergosterol content and unequal inhibition of the three fungal genera used in the inoculum. Fusarium sp. was shown to contain higher levels of this membrane component than Cladosporium sp. and Penicillium sp. For this reason, the most appropriate method overall, giving reliable quantitative results, was deemed to be the image analysis.

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

“…For example, ITs are efficient on filamentous fungi such as Cladosporium sp., Penicillium sp., and Fusarium sp. ; but ITs are not effective on cyanobacteria (Table 1) (Barrionuevo and Gaylarde, 2011). As preservatives, the MIT/CMIT combination is one of the most cost-effective solutions currently known (Karsa and Ashworth, 2007).…”

Varnishes with Biocidal Activity: A New Approach to Protecting Artworks

“…One possible 2 of 15 alternative that has been explored very little is to use materials with biocide incorporated. Restorers often carry out these tasks empirically, mixing them with water repellents or consolidants, but only in the area of mortars for restoration have serious attempts been made to obtain products with biocidal activity [22][23][24].…”