Wood is often covered with a coating in order to protect the surface. Unwanted dark mold growth on paint covered surfaces in external conditions is a familiar phenomenon. Simple microbial techniques have commonly been used to determine the dominant fungal species present in the discoloured area, for example morphological analysis of microscopic preparations of fungal pieces sticking to an adhesive tape. When using this method Aureobasidium is frequently recognized to be the dominant fungus. This is a curious outcome since this fungus can not be identified by its commonly occurring dark chlamydospores but only by the synchronous conidia production from young expanding hyphae. To understand the uncertainties in the diagnostics of the dominant molds on coated wood a case study is done on wood impregnated with raw linseed oil. The reason for selecting this oil treated wood is that raw linseed oil or its fatty acids are a common ingredient of coatings and a quick dense mold growth is assured. Three microbial techniques were used to detect Aureobasidium as the dominant species. The CFU technique based on colony forming unit counts of swap samples indicated a dominancy of more than 50% of Aureobasidium on wood impregnated with linseed oil. Adhesive tape preparation and examination of the culturable fungal microbiota, did not counter this degree of dominancy. The ability of Aureobasidium to grow on pure linseed oil provided supporting evidence of the dominancy of Aureobasidium.

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