Location Affects Performance of Biocide-Containing Paints
Lab tests suffer from two major weaknesses. First, they are generally limited to a few selected organisms, and second the lab does not simulate the migration and depletion pattern that occurs for biocides at the coating surface over many months of exposure. Information on efficacy against the organisms and conditions found in the natural environment is obtained by exposing the coatings under conditions in the field. Field testing using test fence exposures is a common practice in the coatings industry. It is used to assess the long-term performance of a variety of different coatings properties, such as dirt-pickup, microbial resistance, erosion, checking, cracking, chalking, flaking, blistering, fading (color and gloss), and discoloration.
Troy uses field exposures extensively to test its dry-film and wood preservative products in coatings formulations at test sites in seven distinct regions of the world. This paper covers the performance variability of tested paints for resistance to microbial growth at various sites throughout the United States. Acrylic paint containing a number of commercially available dry-film preservatives was applied over cedar test panels and exposed in three distinct locations. Three commercial, top-of-the-line paints were used as positive controls in the study. The results of three identical exposures show that the performance of the paints varied significantly by location and by the type of dry-film preservative used. This variation in relative performance by location was observed for the positive controls as well as the test paint with the various commercial dry-film preservatives. This paper includes information on some of the causative factors for the variation, and shows that reliance on data from only one exposure site can be misleading.