Durability of biocidal agents in facade coatings and their release under real climatic conditions

Growth of algae and fungi is a well known phenomenon on exterior building surfaces. Modern façade coatings, especially coatings based on organic resins, therefore contain antimicrobial agents. The biocides are meant to inhibit or at least to delay microbiological growth significantly. Visible microbiological activity in the form of coloured spots is accepted as deficit in German prevailing law cases. Besides juristic aspects the leaching of biocidal ingredients from coatings may also have environmental effects and points out the necessity for product optimisation to minimize the impact of biocides on water and soil. In a four year outdoor study the behaviour of façade coatings equipped with different biocidal agents was examined. Special test specimen based on external thermal insulation composite systems (ETICS) were designed and furnished with different façade coatings. The coatings contained four different mixtures of biocides. In sum, 20 different types were exposed to real climatic conditions at two locations in Germany. At defined times the biocide content to the coatings was analyzed by high performance liquid chromatography/tandem mass spectrometry (LC/MS-MS). Additionally, the run-off water from the specimen was collected and analyzed. In all coatings the concentrations of the active ingredients declined depending on the type of the ingredient and the matrix. In the run-off water the highest concentrations were found within the first three months of exposure. The results show clearly that the decrease of the antimicrobial ingredients in the coatings can not only be explained by leaching. Other ways of release are also possible, as well as the formation of transformation or degradation products