Coatings applied to building exterior walls are required to maintain aesthetic appearance and durability over long periods. This study focused on “rain streaks dirt” caused by rain, which are more conspicuous than general dirt, and conducted long-term outdoor exposure tests using 32 types of coatings. The results clarified the characteristics and degree of staining for each coating and examined the relationship between streak staining and surface degradation (chalking, gloss retention rate). It was found that coatings with more severe surface degradation tended to exhibit greater staining.
SHIMODA et al. (Sun,) studied this question.