I think it would slow the egress of water very bit as much as the ingress. If you're leaving a piece of oak outside for more than a few days at a time, my opinion is that painting it with anything is a waste of resources. Oak is naturally durable because of its tannin content - especially when not in contact with (bare) earth.Silver seems to be the new black. Are people using clear wood preservative on untreated oak garden furniture? Just thinking it would slow the endgrain from soaking up water. Thanks.