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Thread: Drain leak at slab joint

  1. #1
    DIY Junior Member sdmark's Avatar
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    Default Drain leak at slab joint

    Hi,

    Homeowner and DIYer here. The master bedroom and bath were added in the 1970s. The bathroom sink is on an outside wall. I noticed water on the concrete outside. I removed the siding. At first I thought that the leak might be in the ABS-to-cast iron joint that I installed when I remodeled the bathroom in 1998. However testing showed that the leak is at the bottom of the short cast iron pipe. I had to chip away some mortar to confirm that the cast iron is sitting in a rubber gasket wrapped in stainless steel at slab level. There has been other minor shifting of this wall so there could be an alignment issue, though I don't see an obvious displacement.

    Name:  Drain leak at slab joint.jpg
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    What are my options here? Is there some compound I can use to seal the rubber to the cast iron? Should I try to expose enough of the rubber to get a pipe clamp around it? Do I need to replace the cast iron section with ABS?

    Thanks for your thoughts,

    Mark
    San Diego

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    Looks like wetness above the lower joint. If the pipe were draining properly, there would never be a puddle like that at the top of the lower joint. The cast iron should be a couple of inches into the lower coupling, and water does not flow uphill.

    The top joint should be make with a banded couple to keep the joint aligned. The coupling you have there is approved for use below grade, not inside a wall.

    I would go back and be sure I knew exactly where that liquid came from.

    Last edited by Terry; 10-19-2013 at 07:16 PM.

  3. #3
    DIY Junior Member sdmark's Avatar
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    Hi cacher_chick,

    Thanks for your reply.

    Quote Originally Posted by cacher_chick View Post
    The top joint should be make with a banded couple to keep the joint aligned.
    Is a "banded couple" the one where a stainless band covers the rubber? Like this?

    Quote Originally Posted by cacher_chick View Post
    I would go back and be sure I knew exactly where that liquid came from.
    The water appears when the sink is turned on and seems to be flowing freely. It never backs up into the sink. Does that answer the question?

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    Forum Admin, Expert Plumber Terry's Avatar
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    I would chip that out, replace the couplings and use some ABS pipe there.

  5. #5
    DIY Junior Member sdmark's Avatar
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    Quote Originally Posted by Terry View Post
    I would chip that out, replace the couplings and use some ABS pipe there.
    Terry, do you mean chip through 3" - 5" of cement slab so I can replace that lower fitting? Or is it enough to replace the upper fitting if the lower is not obstructed?

  6. #6
    Retired Defense Industry Engineer jadnashua's Avatar
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    It's possible that the OD of the abs and the CI are not the same. If that's so, then you need to ensure you get a new coupler that is designed to join the two different sizes you have. That coupling, as said, is not approved for that application, and may be weeping if they aren't the same size, no matter how tight you get the bands.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  7. #7
    DIY Junior Member sdmark's Avatar
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    Jim, thanks for your reply.

    The strange thing is that the upper coupling is wrong (no band) but it's not leaking, whereas the lower coupling is right (banded) but it is leaking.

    I installed the upper coupling. It may be sized right--can't remember if I knew already about the different outside diameters of ABS and cast iron.

    The lower one is the original coupling set in the slab and joined to the old cast iron. I would think it was professionally (and correctly) sized.
    Last edited by sdmark; 10-19-2013 at 09:35 PM.

  8. #8
    Retired Defense Industry Engineer jadnashua's Avatar
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    Since water doesn't flow uphill, and there should not be water backup in the drain to cause it to overflow, it makes more sense that it's leaking from somewhere from above.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  9. #9
    DIY Junior Member sdmark's Avatar
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    Jim, not sure what you are thinking might be "above." It's just one sink on this vent stack, and it only leaks when I run the sink; usually it's dry. It almost seems like there must be a partial blockage below grade, maybe even crushed cast iron at the joint. Guess I'll have to pull it apart and look.

  10. #10
    Moderator & Master Plumber hj's Avatar
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    The "Dark spot" on the pipe would normally indicate that the water is flowing DOWNWARD from the improper coulpling. It cannot flow UPWARD out of the lower coupling unless there is pressure on the water, which would only happen if the drain were obstructed. However, it appears that the section of cast iron may have a crack in it where the dark spot begins.
    Licensed residential and commercial plumber

  11. #11
    DIY Junior Member sdmark's Avatar
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    Good catch, HJ. On closer inspection, the cast iron is cracked from top to bottom:

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  12. #12
    DIY Junior Member sdmark's Avatar
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    Got the cast iron out and after vacuuming out debris and a little hand snaking, confirmed with a garden hose that the water drains freely.

    I couldn't see how to tighten the nut on the existing, lower coupling without tearing out the tiled bathroom wall (see nut in upper right of first picture below). Fortunately the ABS fit snugly into the existing coupling. I added a pipe clamp around the very top of that coupling, where a little rubber was exposed. Then I put in the ABS with a new upper fitting. Ran the sink for a few minutes: no more leak.

    How does that look? Anything else I need to do before I re-attach the exterior siding?

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    Name:  Drain leak at slab joint - new pipe.jpg
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  13. #13
    DIY Senior Member dj2's Avatar
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    It looks fine. Run this test for leaks: plug the sink and fill it to the top with hot water. Then unplug it, let the water drain as one and check for leaks.

    Another thing: why didn't you use an ABS coupling at the top connection from old ABS to the new ABS?

  14. #14
    DIY Junior Member sdmark's Avatar
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    Quote Originally Posted by dj2 View Post
    It looks fine. Run this test for leaks: plug the sink and fill it to the top with hot water. Then unplug it, let the water drain as one and check for leaks.
    Thanks, dj2. Bone dry outside after that test. I did have a little rusty water on the inside floor earlier, and the joint from the P-trap to the wall was a little damp just now. I'm thinking that was from when I was pushing and pulling from the outside, trying to wedge the new ABS section under the existing ABS. I'll use my high tech monitoring tool (toilet paper on the floor) for a day or two to see if that leak returns.

    Quote Originally Posted by dj2 View Post
    Another thing: why didn't you use an ABS coupling at the top connection from old ABS to the new ABS?
    Too tight. That lower section is about 10 1/2" of ABS, set into the lower coupling about 1". Right above the upper coupling is the sink drain going through to the inside wall, and above that is more cast iron to the vent. I barely managed to squeeze the ABS in there by cutting the ABS 1/2" short and rolling the rubber coupling back on itself. Hope that's the right way to do it?

  15. #15
    Retired Defense Industry Engineer jadnashua's Avatar
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    It's much better to not have that big of a gap between the pipes...there is a thin stop inside of the coupling and you only need about 1/8" or so. To get things to fit, you can loosen the reinforcement collar, slide it off, then you can deal with just the inner rubber, and it's fairly easy to get things to fit, then slide the reinforcement back in place and tighten it up. The gap gives things a place to catch, but there shouldn't be much in there, so I wouldn't lose any sleep over it.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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