Effectiveness and durability of biocides in building coatings - biological aspects

In 2004 an interdisciplinary publicity funded project on the effectiveness and durability of biocides in building coatings was started at the Fraunhofer-Institute for Building Physics in Holzkirchen, Germany. Material components, building coatings and biocide combinations were chosen and samples for outdoor weathering experiments were also designed, all in cooperation with partners from the industry. About 350 biocide-equipped samples together with control specimens without biocide were exposed to real climatic conditions at two locations in Germany. Emerging microbiological growth on the samples was assessed, according to a self-developed special scale. The periodic assessment tool place in monthly/two monthly (first location) and half-year cycles (second location), respectively. For different samples of the biological colonization could be detected. Whereas the conditions in Germany for growth on outdoor surfaces are best in the autumn, they stagnate or diminish in the dry seasons, winter and summer. All biocide equipped coatings showed, as expected, a retarded growth. However, some characteristic differences could be recognized which could be assigned to different features of the coatings and to different combinations of biocides.