I am in the process of cleaning up the basement and have found a few joists which have some brown/dark green growth/flaking. It scrapes right off with a wall paper scraper. On the 4 or 5 joists which have this it's only on one side. Initially i though the joists may have been painted before. I really don't see any reason for these joists in particular to have been wet or reason for mold but can't explain what else it might be? Is it safe to continue scraping this off? I am planning to paint the cement walls/floor and overhead joists and floor boards.