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The research complements a study (Pinna et al., 2012) carried out to evaluate the effectiveness of mixtures of consolidants and water-repellent products (tetraethylorthosilicate, methylethoxy polysiloxane, Paraloid B72), with biocides (tributyltin oxide, dibutyltin dilaurate, copper nanoparticles) applied in situ to prevent biological growth on stones. The mixtures were tested over time on trial areas of three substrates - marble, sandstone, and plaster – in the archaeological site of Fiesole (Firenze, Italy). The 8-year-long study showed that the recolonization of the three substrates after the conservation treatment related mainly to their bioreceptivity and to the climatic conditions. Although the mixtures of water repellents and consolidants with biocides and copper nanoparticles were effective in reducing the recolonization, they did not play a crucial role in preventing biofilms and lichens growth. This study demonstrated that it was not possible to draw common conclusions regarding the products’ performance on the examined stones. Copper nanoparticles proved to be a suitable alternative to traditional biocides because they did not alter stones colour and contributed to the prevention of recolonization. The study provided information on the succession of fungi and lichens on untreated and treated stones, as well as on the variations of water repellency of treated stones. [ABSTRACT FROM AUTHOR]

Abstract: In this study, some mixtures of consolidants or water-repellent products and biocides developed to prevent biological growth, were tested over time on three stone substrates with different bioreceptivity. The performance of both traditional (tetraethylorthosilicate, methylethoxy polysiloxane, Paraloid B72, tributyltin oxide, dibutyltin dilaurate) and innovative compounds (copper nanoparticles) was assessed using colour measurements, the water absorption by contact sponge method, and observation under stereo and optical microscopes. The application of the mixtures had also the purpose of controlling re-colonization on stone after a conservation treatment. The study site was the archaeological Area of Fiesole; the mixtures were applied in situ to sandstone, marble and plaster which had been cleaned beforehand. An innovative aspect of the study is that, by using non-invasive methods, it also permitted monitoring the mixtures'' effectiveness in preventing biological growth. The monitoring results made it possible to assess the bioreceptivity of the treated stones (sandstone, marble, plaster) over a period of almost three years. The results showed that the mixtures of consolidants or water-repellent products with biocides were effective in preventing biological growth on both a substrate with low bioreceptivity like plaster and a substrate with high bioreceptivity such as marble. The innovative mixture of nano-Cu particles with a water-repellent yielded good results in terms of preventing biological colonization. Moreover, they apparently did not affect the substrates'' colour. Mixtures of nano-Cu particles with a consolidant and a water-repellent hold great promise for preventing re-colonization of stone after conservation treatment. [Copyright &y& Elsevier]