Drain leak at slab joint

Discussion in 'Plumbing Forum, Professional & DIY Advice, Tips & ' started by sdmark, Oct 19, 2013.

  1. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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.

    Drain leak at slab joint.jpg

    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. cacher_chick

    cacher_chick Test, Don't Guess!

    Messages:
    3,236
    Location:
    Land of Cheese
    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.

    [​IMG]
    Last edited by a moderator: Oct 19, 2013
  3. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    Hi cacher_chick,

    Thanks for your reply.

    Is a "banded couple" the one where a stainless band covers the rubber? Like this?

    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?
  4. Terry

    Terry Administrator Staff Member

    Messages:
    14,758
    Location:
    Bothell, Washington
    I would chip that out, replace the couplings and use some ABS pipe there.
  5. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    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.
  7. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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: Oct 19, 2013
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    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.
  9. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,240
    Location:
    Cave Creek, Arizona
    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.
  11. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    Good catch, HJ. On closer inspection, the cast iron is cracked from top to bottom:

    Drain leak at slab joint closeup.jpg
  12. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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?

    Drain leak at slab joint - open.jpg

    Drain leak at slab joint - new pipe.jpg
  13. dj2

    dj2 Member

    Messages:
    398
    Location:
    California
    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. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    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.

    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. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Messages:
    21,802
    Location:
    New England
    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.
  16. sdmark

    sdmark New Member

    Messages:
    16
    Location:
    San Diego, Calif.
    I actually started with 3/8" but had to cut another 1/8" to let the thin stop get in between the pipes and get the pipes aligned ... so maybe my initial measurement was off, or it didn't go as far down into the bottom coupling as I thought it would.

    Exactly what I did. I didn't find it very easy since the bottom coupling was set in cement and the pipe just above the top coupling was vertically constrained by the Y (?) going through drywall. Basically I had to get a 10 1/2" pipe into a 10" almost-rigid gap.
    Last edited: Oct 20, 2013
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