What to place behind my lower T1-11 OSB Siding?

Repair help for the do-it-yourselfer.
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Posts: 12
Joined: Wed Feb 10, 2016 2:19 pm

Fri Feb 03, 2017 12:02 am

We've had a bit of moisture lately out here in AZ and I notice some warping of my lower trim where the t1-11 siding meets the CMU block skirting. Upon inspection the trim disintegrated in my hands revealing water saturated siding on the lower 6" or so of the T1-11 OSB style siding. I opened up all the trim down that particular side of our Palm Harbor double wide to let it air out and put a fan on the worse part. I had a water restoration guy come out with his fancy moisture gages and thermal imaging and check it out and he recommended a sealer along the lines of Red Guard to create a membrane before I put new trim back on and re-caulk. It sounded good until I looked up Red Guard and see what it's really designed for and I lack confidence in this product for this particular situation. Instead I was thinking I might pry up a little on the siding and try to fish some tar paper up under the T1-11 so that it overhangs the rim joist and the filler 2x6 (kind of like a sill plate between the home and the block skirting). I figure that's probably better than slathering everything up with a paint like material... I don't know though. Any thoughts?

I guess the main concern for me is to prevent further damage to the rim joists (which are good for now) and the filler (sill plate) between the block stemwall and the home which is pretty much rotted out but serves no purpose to my eye other than to fill the gap between the cmu and home [???].

My other fear is that prying on the t1-11 to try to insert some tar paper may destroy the siding since the bottom 6" at some places has seen to much water and will likely crumble in my hands.

Thoughts are most welcome as I'm tackling this project this coming Saturday.


Posts: 38
Joined: Wed Aug 03, 2016 10:29 am

Fri Feb 03, 2017 4:17 pm

When I redid my master bath I was going to use Red guard but then went with the kirdi system.
I have seen people waterproof a lot of things with the red guard but never used for an outside wall.
In theory it should work, but I would rather use a membrane or tar paper in your case.

Posts: 80
Joined: Tue Oct 20, 2015 11:02 pm

Fri Feb 03, 2017 5:40 pm

Replace belly band with HARD Plank or use T 1 11 again, but before installing run bead of high quality caulk (such as Valkum) at top edge on the back side of belly band you are re installing so it squishes out the top and then come back and run another bead across the top after installation.
Regarding sill plates, replace with pressure treated and make sure they are tight fitting (use wedges) every 4ft on center and each side of door and window openings.

With T-1-11 you will need to fill all divots in siding at intersection of belly band and siding and slope so there is not place for water to pond. A carpenters pencil works perfect for the divots (blunt end).

If you follow the above procedure there is no need to try and work a flashing up behind existing siding assuming of course you do perform some regular maintenance on you house.
Enjoy your weekend.
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Posts: 80
Joined: Tue Oct 20, 2015 11:02 pm

Sun Feb 05, 2017 10:49 am

I should add to thoroughly paint belly band before installing, front,back,bottom and butt joints and area to be installed over, preferably two coats on all areas before install.

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Location: Weedsport, NY

Sun Feb 05, 2017 12:30 pm

Also make sure the skirting is properly vented. You may also have moisture going up from the ground.

"If I can't fix it, I can screw it up so bad no one else can either."

Posts: 12
Joined: Wed Feb 10, 2016 2:19 pm

Mon Feb 06, 2017 10:16 am

Thanks Yakima, good stuff there!