Question about inspection hatch in slab

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by lucgallant, May 20, 2015.

  1. lucgallant

    lucgallant New Member

    Joined:
    Jan 22, 2011
    Occupation:
    Electrical Engineer
    Location:
    Fort McMurray, Alberta
    Hi everyone,

    I've got a question about a situation in my washroom. I know it's not a 100% plumbing question but it definitely ties to my plumbing system. I know it's a bit long but I wanted to provide all the detail.

    See the attached photo.

    100_7433.JPG This is a photo of a renovation I was doing 3 years ago. This photo is before I poured self levelling concrete. Today, the inspection hatch on the lower left is still accessible, and the inspection hatch on the upper right has been covered over, which I had discussed with my plumbing inspector.

    In the lower left hatch, there is a check valve. This check valve separates the weeping tiles from my sewer system. This is looking down into it. Note that the 4" threaded cover is removed in this photo.

    100_7432.JPG

    The configuration of my washroom today is, I've got the galvanized metal cover installed on the square inspection hole, and I've got sheet vinyl flooring laying overtop. I did not glue the flooring down in any way because I had to keep the check valve accessible.

    The washroom has been finished for 3 years. When I recently lifted up the flooring for an inspection, I saw some black mould on the surface of the concrete and on the underside of the flooring. I lifted up most of the rest of the vinyl flooring in the washroom, and the mould is strictly between this square inspection port, and the nearest edges of the flooring. I cleaned everything with bleach and water and there aren't any signs of it left, except for minor staining on the underside of the vinyl.

    My (unsophisticated) theory is that the air from under the slab is making its way along the slab/vinyl and leaving moisture behind which is turning to mould. I am 99.99% sure it is not water rising up as we would have seen it, and the area here is quite dry. My idea of a plan, is to apply a bead of acoustic sealant, between the concrete edge and a square sheet of vapour barrier. Then, rest the galvanized panel over top. So in the future it would still be inspectable however no air from below the slab could reach the flooring. This could be consistent with the vapour barrier installed on the underside of the slab.

    The only other location where the underside of the slab exposed to the inside of the house is under the shower, however this leads up into the interior wall space so I'm not concerned about mould there.

    Thanks in advance everyone for your input on this. I'm usually very versatile but this one caught me a bit off guard.
     
  2. hj

    hj Master Plumber

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    IF that is a check valve, then it is frozen in the open position, because the flap SHOULD be hanging down in the pipe.
     
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  4. lucgallant

    lucgallant New Member

    Joined:
    Jan 22, 2011
    Occupation:
    Electrical Engineer
    Location:
    Fort McMurray, Alberta
    Hi there,

    I might have used the wrong word when I wrote "Check valve". The flap is currently on its stop, it can't go down any more. It blocks water from the horizontal pipe (going up in the picture) from going downwards (into the picture). I can only suspect that the downwards pipe come from the weeping tiles, whereas the horizontal pipe (going up in the picture) goes to the sewer system. When I poured water in the horizontal pipe I heard it go into the sewer system via the toilet flange when I had it off.

    Any ideas on sealing the opening with acoustic sealant?
     
  5. hj

    hj Master Plumber

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    That description of the water flow is completely undecipherable. That flap looks like it would have to allow water to come up INTO the concrete box, but not drain out again, which makes no sense.
     
  6. lucgallant

    lucgallant New Member

    Joined:
    Jan 22, 2011
    Occupation:
    Electrical Engineer
    Location:
    Fort McMurray, Alberta
    See this sketch.

    The sketch is drawn looking from the left side of the image. Keep in mind in the picture above the 4" cap is removed. Also if you zoom in to the picture above you'll see there's an outlet right above the flap, kind of where that dirt is.

    Sketch214165752.png
     
  7. hj

    hj Master Plumber

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    Well, that may be tje dumbest thing I have ever seen. The only way "weeping tile" can build up pressure to open that check valve is if the water is HIGHER than the flap, which means the whole aeea is under hydrostatic pressure and the weeping tile is completely flooded and useless.
     
  8. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    That flapper is way below the floor surface, so I think the perimeter drain tiles will be useful.
     
  9. lucgallant

    lucgallant New Member

    Joined:
    Jan 22, 2011
    Occupation:
    Electrical Engineer
    Location:
    Fort McMurray, Alberta
    To be real honest, I don't even know what's on the lower part of that flap. I suspected weeping tile, and the plumbing inspector kind of had agreed. At that point, the flap is probably about 6.5' below grade. Whatever the purpose of the flap, the original question was regarding humidity in the hole :)
     
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