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Newly built crawl space, decking on, RAIN, now floor joist mold

Tapcon | Posted in General Questions on

Walls not even up yet. Unvented crawl space has concrete floor with vapor barrier under it. Had not installed rigid foam yet to the walls. Floor drain turns out not to be at lowest point within the entire perimeter. 3 heavy rains. 
Now have condensation all over the underside of the decking and floor joists slimy with mold. A real mess and I’m trying to figure out what to do next. Any help appreciated.

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  1. Jon_R | | #1

    Pump out any water and, assume the crawl space is sealed up, install a dehumidifier.

    1. Tapcon | | #6

      OK, I will definitely get rid of standing water. Problem is the crawl space is pretty porous with only the subfloor, with 1/8th inch between panels and an access panel.
      I had been using all my energy into clearing the rain puddles off the deck, having put plastic vapor barrier over much of the deck to modest success, little realizing the true damage was being done below.

  2. Expert Member
    BILL WICHERS | | #2

    You could try using floor leveler to build up the high spots a bit so that the drain will end up at the lowest point. You don't ever want any standing water in your crawl space. Once you have that issue solved (and part of "solving" that issue is fixing any exterior drainage or grading), then I'm with Jon -- install a dehumidifier in the crawl space.


    1. Tapcon | | #4

      I was mulling the use of a floor leveler. But what I probably need is a slope toward the drain. There are several depression areas in the concrete floor. So I was also mulling some type of channel from those depressions to the drain. Is there a machine that would act like a wood router into concrete?

      Until the wall and roof gets on, the subfloor is going to leak into the crawl space. So I will take the suggestions offered here and get rid of any standing water. I had left it for a day because there was more rain in the forecast.
      I was stunned to see the entire underside of the decking and the joists after only 24-48 hours. Should I go after the underside of the entire floor with towels?
      I wonder if I have to have a hazmat suit or at least a higher end mask, even to be down there.

  3. trystanherriott | | #3

    I dealt with a similar set of circumstances when I was framing my house. Whenever it rained I pumped the standing water out of the crawlspace, using a squeegee on the concrete floor as needed to work water towards a small (sealed) catch basin we had set before placing the concrete slab. Then I ran big fans to promote drying. Ended up doing this three or four times until we were shedding water off of the roof. We avoided a moldy mess on the floor joists, but it was pretty hard earned.

    I’ve had luck with Concrobium Mold Control, but I’ve only used it for small patches of mold on lumber.

    Good luck.

  4. Tapcon | | #5

    Will the big fans work in an unvented space? There are enough cracks and an access panel. Will a humidifier work if the space is not completely sealed?

    1. trystanherriott | | #7

      My crawlspace is conditioned now, but we clearly weren’t there yet during construction. I do not think dehumidifiers would have helped much to dry my crawlspace while we were framing the walls and roof. When it rained during that framing phase of the build, I set 2 big fans along the crawlspace walls to get a circular flow of air down there after I pumped out the bulk of the rain water. The only opening in the first floor framing is ~4’x10’ where we put access-stairs to the crawlspace. Drying went pretty well with the fans after it’d stop raining and I’d finished pumping.

      I did run dehumidifiers a lot after the house was totally framed and air sealed. Framing lumber and drywall mud and paint made for a pretty humid scene for a few months…that’s when I was cranking the dehumidifiers!

  5. Tapcon | | #8

    Thanks for the suggestions. I'm going to get rid of standing water via squeegee and shop vac. Then try the fans. Big job to try to clean every joist.

    1. andy_ | | #11

      Once the water is gone and the house has a roof, those joists will dry. Mold needs moisture to grow. If it's still there and you want to get rid of it you have a few options.
      Professional remediation. Which can be anything from a bunch of minimum wage dudes with spray bottles of bleach to dry ice blasting. Priced accordingly.
      DIY. Bleach, water, and dish soap mixed together in a pump sprayer will make quick work of the mold, but not sure I'd want to be doing that in such a confined space. Vinegar is another mold cleaner that won't kill you, so you could try that too.

  6. Patrick_OSullivan | | #9

    Not for nothing, but did the framers make no attempt to tent the deck ahead of the rain?

    1. andy_ | | #10

      In all fairness, I don't think I've ever seen that done on new construction.

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