because it holds up well to the water and general use but I used it once on the exterior and it was a disaster. It held up well but when it went south, starting at the joints and working away, it was really three times as hard to remove. I had to strip the bow spirit back down to bare wood to start over with regular varnish. I was going to use Awlgrip again but after loosing so much wood to the process I decided it was better to just use regular varnish. I hit it with a heat gun and it acted like plastic and came off in hard chips taking wood with it. Not a good situation for someone who wants to keep his boat for any length of time and not wanting to replace a bunch of teak in a few years. Stick to regular varnish on the exterior. IMHO.