We bought a new house last year and I finally got around to working on the deck. It's a pretty large deck and it has an underdeck awning system. I replaced numerous boards and it's ready to refinish. We'll probably have to replace it before too long, but I'm hoping to extend the life a little. We don't use the "room" below for anything more than additional garage-type storage. It had screened in walls that the previous owner covered with Plexiglas, so in theory its a dry area. It makes for a nice storage area.

The underdeck system was leaking in many places from outside the gutter part of it (none elsewhere). I had some siding guys come in (mainly to seal a leak into the house) and they managed to seal up everything except three of the main support posts. I pulled the boards from around them and found one in bad shape (see the first picture, just rained so they are wet). The post itself is very sturdy, but you can see the underside has some rot. I see no need to replace the post at this time, but it needs to be sealed. Water just pours down the post. The other two posts (one in the second pic) were caulked by the siding guys, but they did it while it was wet (why, I don't know). I took a chance it might be ok, but obviously not.

Rather than try to caulk the area I thought I could try some of the expanding foam. Many are waterproof (or at least state they are water resistant to cover themselves). I can't get complete access to all the posts without tearing up some boards and having to replace them. I'm hoping I can spray the foam in to seal up the area.

Any thoughts on how successful this might be or do I need to try and use waterproof caulk?

Pic 1.jpg Pic 2.jpg