Algal defacement of facade materials – results of long-term natural weathering tests obtained by new diagnostic tools

The growth of algae on facade materials has developed to a serious, primarily aesthetical problem over the last decade. Responsible for the substantial increase in biologically soiled facades is the extended presence of humidity films on the building envelopes. Because of the high insulation levels required by law surface temperatures of new or renovated buildings fell significantly. Moisture films caused by driving rain and condensate dry only very slowly and are the most important pre-condition for algal growth. Until today only biocides offer reliable protection against algal growth. Their antimicrobial effect however is only of limited duration because they have to be water-soluble and get washed out over the time. To avoid guarantee claims manufacturers of facade and coating materials are looking for alternatives. Strategies followed include the alteration of the hygrothermal properties of the products and creating self-cleaning surfaces by copying the "Lotus-effect" or by using the photo catalytic effect of Titan dioxide. At the university of Wismar a wide range of innovative products were evaluated in long-term natural weathering tests. Because of their high popularity and cost effectiveness research focused on all kinds of ETICS. In a variety of studies the influences of chemical, hygrothermal and surface parameters on the antimicrobial effect were quantified. The retention periods of water films on different surfaces caused by driving rain and condensation were measured in the laboratory and on site and the data compared to the results of numerical simulations. In order to evaluate the antimicrobial effect in a very early stage new diagnostic tools like Pulse-Amplitude-Modulation-Fluorescence and DNA-analysis were adjusted to the special diagnostic purpose and refined. Results from long-term natural weathering tests and laboratory experiments show that both methods allow the assessment of products a long time before the algae get visible with the bare eye. Combining laboratory tests and efficient diagnostic tools testing cycles can be shortened significantly and product development can be advanced.