My beautiful Knotty Alder patio doors appear that dirt or mold has penetrated the linseed oil we applied to them before hanging them. How can I clean the doors? What should I use to clean them?
Turpentine, mineral spirits, or the vaguely termed "paint thinner" should be effective at stripping the oil from the door.
Linseed oil is prone to developing mold and mildew, you may want to consider refinishing with a product meant for outdoors (I wouldn't recommend spar varnish if it's exposed to direct sunlight though).