We are in the process of purchasing a log home, and there are several ceiling beams on the inside that have black all over them. We’ve tried two-part bleach to no avail. My husband sanded a bit but the black goes very deep and now we’re not sure whether the beams are rotted, or this is mold, etc. Any idea of what it is and how to get rid of it, if possible? Thanks so much for your insight.