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Thread: Moisture in basement room under concrete patio

  1. #1

    Default Moisture in basement room under concrete patio

    Hi all,

    I am trying to help solve a moisture problem in my in-laws basement. They have a concrete patio and a small room (not cold cellar) underneath it in the basement. My FIL (father-in-law) is replacing the drywall ceiling and had originally installed (in order attached to the underside of concrete)
    (1) black roofing paper, (2) 2" rigid insulation in between 2x4s (screwed flat), (3) tuck taped seams, (4) vapor barrier, (5) strapping perp. to the 2x4s.

    Moisture started to collect on the VB between it and the insulation. Researching this I'm now aware the VP and insulation together created a problem (essentially double VB). Removing the plastic seems to solve a fair amount of the problem, however ther are still some spots where moisture is collecting in some of the seams covered by tape. It's a fair amount because when removing the tape it drops to the floor in a small stream.

    A few questions:
    Any thoughts on why moisture is still collecting?
    Could the roofing paper also be causing a problem? The tuck tape on the seams?
    Can I use spray foam to fill any gaps?

    Any other thoughts or comments are appreciated.

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  3. #2
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    Default Re: Moisture in basement room under concrete patio

    Where is the water coming from? Rain seeping through the concrete? Condensation of water in the air?
    Jim
    --------------------------
    Wood, the final frontier

  4. #3

    Default Re: Moisture in basement room under concrete patio

    Quote Originally Posted by kerfin View Post
    Where is the water coming from? Rain seeping through the concrete? Condensation of water in the air?
    Thanks for your reply.
    We've been getting a lot of rain lately so it's a little difficult to tell if it's that or condensation since we removed the VB. If we get another hot dry spell and the moisture is still there, then I'd guess it's condensation. The concrete pad doesn't have any visible cracks.

  5. #4

    Default Re: Moisture in basement room under concrete patio

    Sounds like you did a good sealing and insulating job on the inside so condensation is not likely.

    More likely is that water is seeping/wicking through the slab.
    Concrete slabs used as roofs and exposed to the elements need some type of waterproofing on the top side.

  6. #5
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    Default Re: Moisture in basement room under concrete patio

    It's leaking from above. All concrete has cracks...period, even if you can't see them. In order to get condensation, you need warm moist air coming in contact with a cold surface. Unlikely in this situation presently.
    Paul

  7. #6
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    Default Re: Moisture in basement room under concrete patio

    We had a problem like that once. Tore out the drywall, insulation and vapour barrier and isolated the leak during the next rainfall. Turned out to be an easy fix.

    Condensation can also come from outside of cold water pipes in a space like that.
    Jim
    --------------------------
    Wood, the final frontier

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  9. #7
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    Default Re: Moisture in basement room under concrete patio

    Concrete is NOT waterproof. If it was there would be no need to spray or brush water proof membranes on concrete foundations. Foundations are vertical and leak. Just imagine your in law's horizontal situation and water sitting on it. Sit a lawn sprinkler on top and duplicate a rain,,,,, but get an umbrella first.
    "Do it Right!"

  10. #8
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    Default Re: Moisture in basement room under concrete patio

    To be able to eliminate moisture/ condensation on concrete you need to have intimate contact with it. The products you used are a step in the right direction- but to do it properly you need to apply close cell spray foam directly to the concrete. This stops any possibility of a dew point and eliminates air movement/ condensation because of the thermal break provided by the spray foam. The close cell foam should also provide a certian amount of water proofing but, as mentioned above concrete wicks water and does leak. A good water proofing product on the outside should help a lot.

    When you frame it after the spray foam make sure that no wood is in contact with the concrete. Organic matter and concrete don't mix.

    Another question- is there enough air flow in as well as out of the room?

  11. #9
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    Default Re: Moisture in basement room under concrete patio

    Definitely need to seal the OUTSIDE. Think of concrete as like a real hard sponge. Transmits water but at a very slow rate. If you had just a crack, you'd see it coming thru even more discernably.
    Kevin

  12. #10
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    Default Re: Moisture in basement room under concrete patio

    Further, you may want to see what CMHC says about this or has available.

    http://www.cmhc-schl.gc.ca/en/corp/faq/faq_003.cfm#14


    My basement is always damp, and there are even pools of water standing on the floor sometimes. What information do you have that could help me fix the problem?
    CMHC has published an excellent guide on moisture problems in basements. The guide "Investigating, diagnosing and treating your damp basement" takes you through all the steps you need to solve problems with water in your basement. The first part of the book helps you to figure out exactly what kind of moisture problem you have in your basement. The next part gives you all of the possible causes for each kind of problem, and helps you to diagnose which is the most likely cause. The last part of the book provides several solutions for each cause, ranging from inexpensive fixes to more complete repairs. You can order this publication Online through CMHC’s Publications and Reports section, or you can call CMHC to order it at 1-800-668-2642.

    http://www.cmhc-schl.gc.ca/publicati...ech/92-200.pdf
    Last edited by Lost in the Woods; 08-12-2012 at 12:57 PM.
    Kevin

  13. #11

    Default Re: Moisture in basement room under concrete patio

    Thanks to all for the great feedback. I'll talk to my FIL about sealing the concrete as that sounds like the most obvious first step.

    Thanks again.

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  15. #12
    Join Date
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    Default Re: Moisture in basement room under concrete patio

    I saw in early stage of building the foundation people put a simple plastic film (like a construction membrane) between concrete and the ground. This keeps moisture from damaging the concrete, floor and any other materials. But this seems to be impossible in your case

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