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Thread: How to seal leaking PVC joint?

  1. #1
    DIY Junior Member
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    Default How to seal leaking PVC joint?

    I have a 5-yr old house. We just opened up a wall above a shower to find the source of moisture wetting the wall board and discovered that a PVC vent pipe in the ceiling is leaking condensate. The leak is at a joint between a horizontal piece of pipe and the elbow that turns upward. What cement or caulk can I use on the outside of the pipe to seal up this leak? Thanks for any help.

  2. #2
    DIY Member casman's Avatar
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    Given the location, I would suggest cutting out and replacing the joint rather than glue or caulk cause it might not hold...good luck

  3. #3
    Plumber, Contractor, Attorney LonnythePlumber's Avatar
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    Default No Cement for Condensate

    Condensate comes from different temperatures and not from having a leak in a pipe. You don't need this moisture in your ceiling and it is probably an indication of lack of ventilation. Think about this some more.

  4. #4
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    Default How to seal a leaking PVC joint?

    Let me explain a bit more. There is no doubt that the joint is leaking. I can see it dripping. The pattern of mold that resulted from the wetness inside the wall is consistent with the observed location of the drip from the joint. My contractor's explanation, which I believe is true, is that moisture inside the vent pipe condenses when the air temperature turns cold (below the dew point in the pipe)(at night or behind a cold front). That fits with my observation that the sudden worsening of the wetting of the drywall occurred right after the outside temperature turned cold. So, what I need is a glue or caulk that I can apply to the outside of the joint. It might be possible to cut out and replace the leaking area, as another reply suggested, but it would be very difficult given the location of the pipe between floor joists. Thanks again for your help.

  5. #5
    Retired Defense Industry Engineer jadnashua's Avatar
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    Default

    As Lonny said, if it is condensate, it isn't a leak. That doesn't discount that you have moisture dripping off of it, though, but if it is moisture that has condensed out of the air, no amount of tweaking the joint will help. IF it is condensate, that means that moisture laden air is getting into the wall/ceiling. Fix that, and you'll stop the dripping. The fact that you notice it at the joint horizontal to vertical is the nature of the water coming down the pipe, it comes off at the angle change/joint. A vent does not contain liquids (except possibly whatever may condense out of the vapor). If it really is coming from inside the pipe, you'll have to replace the joint.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  6. #6
    Plumber, Contractor, Attorney LonnythePlumber's Avatar
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    Default You Know what I Don't

    You may know it is not leaking because you see it drip but many people falsely presume that a leak is located where you notice it drip. Condensation on the outside of the pipe would drip like a leak even though it was coming from a higher source. But you can see it and are probably right. You cannot repair a leaking PVC joint without replacing it.

  7. #7
    Moderator & Master Plumber hj's Avatar
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    Default leak

    If the joint is so poorly connected that the minimal amount of water from condensation causes it to leak, then you have a bigger problem. The pipe is either backpitched so the condensate is accumulating in a pool, or there is some other reason why it is not draining back down the pipe without leaking. The only condensation would be from the piping above the leak, and from your description that pipe should be so short that there should be almost no appreciable amount of condenastion from it.

  8. #8

    Default

    IF you can determine that it IS a leak, and can dry it very well and keep it dry for a few hours, you may want to try Marine Epoxy. I have used it on several ocassions and it was fine. Plumbers hate it because the best way to fix it is to cut it out; however it sounds like it's between floors and it may be worth trying the Epoxy and watching it for a month or so. You can get it at Ace hardware.

  9. #9
    Plumber jimbo's Avatar
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    Default

    Let me offer 2 cents worth:

    Condensation is caused by WARM moist air contacting a COLD surface. So, I believe the homeowners observation is correct: warm moisr air INSIDE the pipe is condensing because the pipe is COLD due to cold air in the attic space.

    It is also true that for the joint to be leaking from this relatively modest amount of water, the joint must have really been lousy.

    Although this will not be favored by a lot of professionals who read this forum, I would agree with the solution to try some epoxy putty. This is one case where there is such a thing as just using common sense.

    Given the really bad joint as we mentioned, I would have some concern for the general condition of the rest of the system. It should be looked at.

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