To seal the seam between a doubled joist or beam, what type of caulking is best? The Home Depot Decks 123 book recommends Alex Plus (acrylic latex plus silicone) while a guy at Home Depot suggested Mono Ultra Exterior (latex). How about Blueskin?
I initially used Alex Plus, it rained before the caulk cured, the caulk became a shriveled and cracked mess, I scraped it and replaced it with Mono Ultra Exterior.
Maybe I'm just sloppy, but I've never bothered to caulk the seam on a doubled up joist with treated wood.
There was one time I felt I needed to worry about that, but that was with a cantilevered deck using untreated wood. In that case I just used aluminum flashing over the top of the joists.
I suppose if I were going to caulk it though, I would use a silicone caulk over a latex caulk since they generally adhere and hold up to water better (cleanup is messier, but it's a deck, so it probably doesn't matter).
