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I'm doing a basement finishing project. When I nailed down bottom plate(treated lumber) for framing, I see some moisture appears after a while, no visible water, right under some of the bottom plates. Before nailing, the basement was dry - no seepage through walls or floor. So I do not know if the moisture is captured temporarily so it will be gone soon or it is coming through floor with nailing.

  • Can anyone have similar experience and know why?
  • If the moisture comes from the nailing, is there a way to seal it (all framing is already done)?

Any help/advice will be appreciated.

Added information:

  • I don't have a sump pit
  • The moisture only appears on two sides - north and west side
  • I think it started appearing after 3 to 5 hours of the installation
  • Along with the same side where moisture appeared, I put test frame with 2 ETA shots about 8 hours ago, but no moisture is detected yet.
  • My house is on a higher ground than street (with retaining walls around the perimeter). So even though basement is still underground, basement floor is almost same level as street. I can tell it because my main sewer pipe is buried under the basement floor.

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  • Before you come back with more information, I'd just like to point out it wouldn't be too hard to cut out and pull a section, including one EAT shot and visually inspect. How far below grade is this floor and do you have a sump pit? If there is significant moisture in your wood, you can usually find out by drilling a hole in it and inspecting the shavings, or even hitting it with a hammer and checking for moisture in the dent. You say you've framed the whole area? Does the moisture appear selectively at all? Like only on certain walls or near EAT shots?
    – K H
    May 19 at 23:49
  • It may also be worth pouring an assortment of different size puddles on your concrete and evaluate how much water is necessary for the visible amount of sponging/seepage and how quickly the exposed dark spot dries up if the water is not replaced/maintained.
    – K H
    May 20 at 0:24
  • Oh and how long were the EAT nails you used?
    – K H
    May 20 at 0:25
  • @K H, - I don't know how thick the concrete slab is. It is 100 year old house and my handyman said it should be at least 4". - I don't have a sump pit - The moisture only appears on two sides - north and west side - I think it started appearing after 3 to 5 hours of the installation - Along with the same side where moisture appeared, I put test frame with 2 ETA shots about 8 hours ago, but no moisture is detected yet. Maybe I will cut out a section with EAT shot and visually inspect.
    – user135339
    May 20 at 2:59
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    Plumbing work just started. There is no water under the concrete slab near moisture appeared. Dirt out of it is just dry.
    – user135339
    May 20 at 12:31
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Pressure-treated lumber is as juicy as a ripe peach. On many occasions I've been splattered in the face while cutting and nailing boards fresh out of a strapped unit. It weights as much as three times a dry board. I'd guess that the concrete is drawing the moisture out of the wood. It's not coming through the nail holes.

Run a fan to circulate things for a few days, and run a dehumidifier if necessary. See what's what then.

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  • How does concrete “draw moisture out of wood” ?
    – Lee Sam
    May 19 at 20:51
  • I highly doubt there is that much water at once coming out of the wood.
    – DMoore
    May 19 at 21:00
  • Have to agree with isherwood, even if bought from a big box store, where stored inside, it's still soaking wet. Many lumberyards store it outside. I did a project with a friend that involved dado-ing substantial groves in PT wood, (4x6's) on my table saw. That stuff was so wet my dust collector (Oneida), couldn't suck out the chips, I had to literally shovel the chips out as it filled up in my table saw. May 19 at 21:45
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    @LeeSam it could be a combination of wood saturation, gravity, and capillary/wicking at the wood concrete interface, the latter being close to "drawing moisture out", and the former two providing a persistent supply.
    – P2000
    May 19 at 22:52
  • you could do a test, weigh a sample of the wood, then dry it in your oven (or on a rack in your dryer) and weigh it again.
    – Jasen
    May 20 at 11:13

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