Evaluation of the efficiency of water-repellent and biocide compounds against microbial colonization of mortars

Mortars are building material with a high primary bioreceptivity and thus, they are easily colonized by different microorganisms. To reduce this problem, especially if it concerns restoration and conservation of works of art, water repellents and biocides can be applied alone or in combination. This paper describes experimental data carried out in laboratory conditions as well as outdoors with artificially infected mortars to reproduce natural colonization. The effects of three hydrophobic compounds (RHODORSIL RC80, HYDROPHASE SUPERFICI and HYDROPHASE MALTE) applied alone or in combination with the biocide ALGOPHASE and with the new water miscible formulation (ALGOPHASE PH025/d) were studied. Effectiveness was compared with the behavior of untreated mortars. In both types of experiments, it was clearly shown that water repellents alone do not stop microbial colonization, while water repellents plus biocides prevent microbial growth. In addition, it was shown under indoor and outdoor conditions that fungi are able to colonize untreated mortars as well as those treated only with hydrophobic compounds before phototrophic microorganisms. No significant differences were observed among the compounds tested in their efficacy in preventing colonization.