Not to sure about that 4 on the Floor. It is used alot in ship-building and other outdoor projects. But not to take chances, we used 2 coats of Watco Danish oil and 7 coats of Helmsman Spar Urethane on the boards. Hope that is enough UV protection. I guess time will tell. We are using 4 boards of purpleheart and 5 boards of Cherry, somewhat like a butcher board effect.

http://s159.photobucket.com/albums/t160/sworden73/