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Building new interior walls in a 1911 basement. Slab is about 1” thick and sometimes moist. I’m planning to use pressure treated 2x4s as the bottom plate with another normal 2x4 sistered on top. Between the slab and the PT board, I’m putting a roll of ComfortSeal sill plate gasket.

My issue is that the 5 hardware stores around me all have damp PT wood. It seems foolish for me to install this while also covering both sides, trapping moisture. When the drywall goes up, it’ll be completely enclosed.

What should I do? Any help would be much appreciated.

Jeremy P. Beasley
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    I suggest that any wood placed in a damp basement will become more damp over time regardless of its condition when installed. – Tiger Guy May 31 '23 at 13:17
  • See also: [Why is there moisture under some new wall plates in the basement?](https://diy.stackexchange.com/q/224555/35141) – isherwood May 31 '23 at 19:00

2 Answers2

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I would not worry about the dampness of the PT. I would be concerned about the dampness coming up from the slab. There should be a vapor barrier, however the age of the home means there is none. The concrete was most likely poured after the home was built . You need some vapor protection so the basement isn't always humid and smelly. To prevent rot of the wood floor over time as well.

I would spray the concrete with a waterproofing sealer. Then put down a heavy plastic barrier like visqueen, sealed at the edge of the walls with a polyurethane caulk. Continue the plastic up the walls about 4 to 5 inches.

Place your PT as you planned. The moisture content of the PT will diminish into the air and then into the subfloor and eventually out. If you have a good crew and can finish sealing everything up in a day or 2 there may be an issue. I would just leave about a week before I covered my subfloor. If you want to feel better about the project, wait a week after placing the PT before continuing any other work.

RMDman
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Pressure-treated lumber is always damp. Soaking wet, actually. Squishy, juicy, wet. It'll leak when you cut it and squirt you in the eye when you nail it. Look into how it's created, in great pressurized vats of solution, and you'll realize that this is practically unavoidable.

That's fine. You want it that way, because if it's already dry it's likely warped. If you install it wet, and it dries slowly, out of the sun, after it's been secured in place, it won't warp as much.

It's rarely an actual problem, even when drywall is installed. As long as the moisture isn't sealed inside some cavity or whatever, it'll eventually dry out. There may be some mold in concealed places, but there's mold everywhere anyway, especially if your slab is occasionally damp.

FYI, sill seal isn't really warranted. It's mostly to seal against airflow at the outside of buildings, such as where sill plates rest on concrete foundations (hence "Comfort" in the brand name--that's not referring to the lumber's luxury). It doesn't do you much good in a basement wall. I've never used it there in dozens of new homes, nor has any inspector I've ever met called for it.

There's also no point to the doubled bottom plate. Interior basement walls are normally built with single treated bottom plates and single top plates. That's all they need.

isherwood
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