Rotted wood repair/prevention - multi part problem

Ok, this may be a bit long winded, so bear with me:
I am renovating a house we have recently bought and fixing many many of the previous occupant's 20+ years of "fixes" and additions. The current problem is, he has built an addition onto the house, but the addition is built on top of part of an outdoor deck. Two of the Three walls sitting on this deck are flush with the edges of the decking, but the deck extends under and beyond the third wall. The bottom of this third wall is rotten, most likely from rainwater getting between the deck boards and the wall. I can put some temporary jacks under the wall (bearing the load from the roof rafters) and replace the rotten studs and plate, but two problems still remain that I think I have solutions for and want to see what others think about them:
1) the sheathing looks like it's not in great shape, not as punky as the 2x4's but not great, I'd like to just seal it up with a resin "wood hardener" that is available (I've seen it by Minwax, but I'm sure others sell it too) instead of having to rip off siding and sheathing and goodness knows what else. Anyone ever try this and does it work?
2) I'm thinking of cutting a 1/4" or 1/2" gap in the decking flush with the edge of the wall (outside). It'll probably mean having to put a pair of joists on either side of the cut (the joists run parallel to the proposed cut). If I did this, put flashing under the plate, gob the heck out of it with caulk - what do you think?
Thanks in advance for any thoughts/advice.
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You need to deal with the rot first, or it might continue underneath the coating you apply. a) You could apply a product called Termin8t [something like that], which is a solution of copper naphthenate that will kill any rot-causing organisms it contacts, and then coat over that. b) If you are near a coast, you might be able to find some epoxy coal tar coating in a marine supply store, and just apply that alone. It is not allowed in inland water boats, though, and it is hard to find sometimes. In the good old days, there used to be a number of good compounds that would do the job, but the enviroweenies and safety nazis have stopped most of them. Best wishes with your project.-Jitney
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louie wrote:

Before doing anything, I suggest that you consider if you should try to "fix" the problem at all. Was the foundation and the deck really designed and built to support a room? I suspect you will have continued problems and you may someday face a building inspector that tells you to tear it down. Was a permit give for the original project?
I would tend to believe the best thing is to tear it all down to the ground and build new from the foundation up. Doing it right means doing it once.
--
Joseph Meehan

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<You need to deal with the rot first, or it might continue underneath the coating you apply.>
Thanks, I hadn't thought of that. I also had a thought that the resin probably wouldn't help if the wood was still damp (it is). I'll have to dry it out first
<Before doing anything, I suggest that you consider if you should try to "fix" the problem at all. Was the foundation and the deck really designed and built to support a room? I suspect you will have continued problems and you may someday face a building inspector that tells you to tear it down. Was a permit give for the original project?
I would tend to believe the best thing is to tear it all down to the ground and build new from the foundation up. Doing it right means doing it once.>
Believe me, I've thought about it, and I agree that it would be the best thing. Money and time are the two things restraining me from doing exactly that (mainly money). I plan next summer to put a block foundation under the portion of the house supported by the deck (currently just posts and joists like most decks). As for the building inspector, well I don't know if there ever was a permit, though I doubt it. Since I don't have the money now to handle a job like that, I'll have to take my chances with any future problems. I don't normally do half a job, but I can't see any way to afford a job of that magnitude right now. In the future, it might be possible. I may have to set aside a savings account for just that sort of problem.
Thanks for your answers so far.
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You might want to drill a narrow but deep hole in the affected area to see how deep it goes, and to check for structural integrity. If it is dry rot, drying it out will not help. It sounds like you need to buy some time. Believe me, I know about money problems, and a quick cheap fix is better than none at all. Dry it out, caulk and waterproof as best you can, and apply the Termin8t (Hardware store, under $10/quart). Some well placed mothballs placed at or very near the rot will slow down, but by no means stop, the deterioration. Save your nickels for replacement the proper way later on.-Jitney.
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I would replace the rotten wood with pressure treated wood that I put 3 layers of oil based poleurathane on first.
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1) Sealing up potentially wet sheathing in what will be a heated space is just asking for trouble. To avoid future problems, remove the plywood to make sure the framing is sound. Replace ALL soft or rotted wood. Make sure everything gets to dry out and treat with some sort of pesticide that contains borax or boric acid. This will not only kill any existing pests, but also ward off fututre infestations of anything from fungus to termites. There are many different brands, see what your local landscaping supplier has. Also check out this info: http://alsnetbiz.com/homeimprovement/woodrot_repair.html
2) Sounds iffy. Keep an eye on it and re-caulk when needed, I guess. It's not the right way, but if you're looking for a short term solution...
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