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Thread: Venting outside with ABS?

  1. #1
    DIY Member Drewski123's Avatar
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    Default Venting outside with ABS?

    Hi,

    When I remodeled my bathroom, I replaced the old cast Iron DWV with ABS. I left the end part intact (cast iron, which exits through the roof). When it rains, the ABS to Cast Iron coupling leaks water, mainly because the cast iron surface is not smooth like the ABS, so there are irregularities on the surface of the pipe, that creates tiny spaces. I tired two different couplings, and it still leaks. So I have decided to remove the end part and replace it with ABS. I've seen some people were saying that you cannot use ABS for venting outside, mainly because of the exposure to the sun. What's your opinion on the use of ABS in this situation? For those in the Seattle areas, does the code allow the use of ABS for venting outside? I know, PVC is definitely OK, but not sure if ABS is.

    Thanks for your help,
    Drew

  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    We use ABS all the time here in Seattle.

    If the outside of your cast is 4-1/8", that considered a copper size. No hub couplings are meant for 4-3/8"
    If that is the case, you can pick up a Mission copper by No-hub coupling, and that's as good as it gets. If the pipe is that rough, it may take some silicone.

    I would have used ABS all the way through the roof.
    Last edited by Terry; 12-06-2012 at 03:04 PM.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    Personally, unless you have the proper hangers for the CI section going through the roof, I would not want it pressing down on my plastic pipes below! That stuff can be quite heavy!
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    DIY Member Drewski123's Avatar
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    Thanks Terry. I have to measure the pipe on OD, but I think it is 4-1/8". So the couplings that I used (flexible coupling as well as shielded coupling - Proflex) were for the new CI size. This makes sense because I could easily move the coupling to each side of the CI while connected, and tightening the couplings did not help much, the rain water was still dripping from the bottom (on the CI connection).

    Jim, the two pipes are connected horizontally right below the 90 degree angle. There is also a support right underneath the CI pipe , so the CI weight does not create any stress on the ABS.

    So, (Terry & Jim) would just replace the CI altogether with the ABS, or replace the coupling with the Mission one, and keep the CI on the end? Forgot to mention the pipe sizes: ABS 3" - CI 4"



    Thanks again,

    Drew

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    DIY Member boardable's Avatar
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    Dreqw, first think is make sure your connector is CI to Plastic. If not it will leak. The fact that it leaks when it rains means that you did not water test it so I am assuming you are doing this without permits. What you need to do is make sure you have the correct no hubs and if there is still a leak you can use a little plumbers putty to finish it off.

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    Forum Admin, Expert Plumber Terry's Avatar
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    if there is still a leak you can use a little plumbers putty to finish it off.
    I've never used putty on a no-hub coupling. I'm not thinking that would go so well.
    If you can use ABS through the roof, that would be the best option.
    If he's trying to seal a leaking no-hub coupling, silicone would be better, though that normally means he has the wrong size on the couplings.
    For old cast, I've found that you can't use couplings for either cast iron or plastic. Most old cast is copper pipe size.

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    DIY Member boardable's Avatar
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    The putty is only on the inside and to "aid" in any deformity in the cast. Terry I go with you, probably the wrong coupler.

  8. #8
    Moderator & Master Plumber hj's Avatar
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    IF you stick the ABS through the roof, then put a coat of paint on it to avoid the UV exposure.
    Licensed residential and commercial plumber

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