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I have a bathroom project in my basement. I made the mistake of not using pressure-treated lumber for the bottom plate. Everything is roughed in, and I have access to the framing since I haven't put up cement board yet.

We do get some leaks in this area when it rains hard. We have recently regraded the ground outside, so hopefully it won't leak anymore, but I have to assume that it will.

I would like to cover the plates with some kind of paint to at least give them some kind of protection from mold. I know that it's impossible to paint the bottom of the baseboards.

What kind of paint should I use to cover these boards? And is there a way to seal the edges to prevent water from seeping in underneath them?

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    I would saturate them with any of the paint on wood preservatives let a little dribble behind at the wall and it just may help the bottom also. I would want to wait to cover things or set it up so the mop boards/trim can be removed if it may end up wet this would be better than the moisture causing trouble you don’t see until the paint starts falling off the Sheetrock.
    – Ed Beal
    Feb 15, 2021 at 22:48
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    What Ed said. Here's one option: truevalue.com/coppercoat-green-wood-preservative-1-gal
    – Blobfish
    Feb 15, 2021 at 23:34
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    Paint doesn't stay on wet things or prevent moisture from wicking up through the concrete, and it's the interior of the wood that rots. You need to either use an absorbent anti-microbial product or not worry about it.
    – isherwood
    Feb 16, 2021 at 14:57
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    A picture would help tremendously. Depending on what's running through the wall and floor (if anything) there, it may be worth cutting out the bottom plate from each stud with a reciprocating saw and replacing it either all at once or in two parts, with PT wood. You may even have room for a membrane between the concrete and the wood.
    – TylerH
    Feb 16, 2021 at 15:05
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    You could treat it with borax/boric acid to prevent fungus and insect damage.
    – dandavis
    Feb 16, 2021 at 19:11

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Depending on the length of the wall, and what's running through the wall and floor (if anything) there, such as electrical or plumbing, it may be worth cutting out the bottom plate from each stud with a reciprocating saw and replacing the bottom plate--either all at once or in two parts--with PT wood. You may even have room for an impermeable membrane/gasket between the concrete and the wood; search for "sill seal" and you'll find plenty of options.

For around $1 per foot of wood you need (plus the cost of any membrane and fasteners you need to buy), it's a pretty cheap solution to achieve peace of mind when it comes to rotting framing in your bathroom.

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  • This is in fact the way I solved the problem. It was moderately difficult but not the worst. I used PVC trim pieces, stacked double, to serve as the bottom plates. It's a small bathroom so the cost of PVC wasn't that big of a deal, all things considered.
    – Mark
    Feb 17, 2021 at 20:28
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I assume you're talking about the bottom or sole plate of framing which is laid horizontally, correct?

If you have wood resting on a concrete floor then there isn't much you can do. The floor will forever wick water into the wood from below and rot it out; even when it's not raining.

If you put some sort of sealant in the corner where the wood meets the floor then you'll prevent excessive water from flowing into the wood but concrete absorbs water and will just distribute it into the bottom of the wood anyways. This would also lock in moisture and prevent any chance of it drying.

If you fully seal the wood with some sort of paint then it will likely hasten the rot since the bottom will still be wet and have no source of fresh air drying.

So, what can you do?

You can buy pressure treatment solution, run thick bead of caulk along the floor 1/4" away from the bottom plate, and pour that solution into the makeshift "pool". You need the wood to absorb this solution so the longer it sits the better. When you're ready then pull up the caulk and finish your renovation.

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