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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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FreeMan
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user135339
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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 '21 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 '21 at 00:24
  • Oh and how long were the EAT nails you used? – K H May 20 '21 at 00:25
  • @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 '21 at 02:59
  • Also, plumbing work starts tomorrow and they need to break the slab on one corner (where moisture appeared) to create a bathroom. When they dig, I guess I will know for sure if there is water. – user135339 May 20 '21 at 02:59
  • 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. – user135339 May 20 '21 at 03:06
  • Yeah you should edit your question to include the extra information. Is there any possibility of in slab plumbing or conduit based on stub ups you see? – K H May 20 '21 at 03:06
  • Oh and have you performed a moisture test on your wood? – K H May 20 '21 at 03:15
  • I drilled couple of holes on wood but I don't see any water collecting there. – user135339 May 20 '21 at 11:59
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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 '21 at 12:31
  • Exactly what I was thinking ... lumber itself has a percent of moisture ... Did it rain recently? Do you live somewhere with 100% humidity I'm from NOLA, lived in TX & AL. Basically, places where less than 100% humidity is an oddity) – Truman HW May 20 '21 at 03:31

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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.

isherwood
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  • How does concrete “draw moisture out of wood” ? – Lee Sam May 19 '21 at 20:51
  • I highly doubt there is that much water at once coming out of the wood. – DMoore May 19 '21 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. – George Anderson May 19 '21 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 '21 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 '21 at 11:13
  • There's nothing to test. Lumber is treated by immersing whole units in water-based solution, then applying huge pressure. There is no drying afterward. Boards are virtually saturated when they arrive at the store and are often visibly wet when pulled from the stack. I've gone so far as to stand joist lumber out to dry just to make it less unwieldy during installation. A 16' 2x10 can weigh over 100 lbs. – isherwood May 20 '21 at 12:49