I've got water damage on the top of beams supporting a 2nd floor deck. The deck sits on 2x10 joists which abut the house on one end and sit atop a 4x10 beam on their outer end. Water is free to run between the deck boards and fall on top of the 4x10 beam. The top of that beam (painted Doug Fir) is starting to rot from the water pooling on it. Also, some of the joist bottoms, where they sit on the beam, are rotting. I can repair the rot damage with Abatron WoodEpox and some additional wood and hardware, but I need to find a good way to waterproof the beam top between the joists. As I repair the damage I can give it a slight curve so water will run off but I still want a waterproof membrane that I won't have to mess with for many years. Any ideas?