I have installed a 8” pine log sliding 1” thick in the middle with a 1/2” overlap. I used Cetol 1 and put 2 coats on it the first year. I was planning on putting on a third coat last year when I noticed some black spotting ocurring. It would appear most of the spotting is ocurring half way down from the top and arround decks. This pine was kiln dried prior to us milling it into sliding. It also sat in my garage for 4-6 months prior to installing it on our cottage. I have pictures I could email y