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Thread: non standard cast iron pipe size leaking

  1. #1
    DIY Member pronouncedeyen's Avatar
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    Default non standard cast iron pipe size leaking

    I have a cast iron waste pipe that has a leak in it. It's behind a wall that we were going to rip out anyway so I took my sledgehammer to it and exposed a 5 ft section of it. It's a mess. It must have been leaking for awhile because it's all rusted on the outside and seems to be leaking in 2 or 3 places.

    I decided to run to Home Depot and pick up a 3" PVC pipe and 2 Fernco's to splice in. When I got home I noticed that the iron pipe seemed a bit narrower. I measured it and instead of the outer diameter being 3.5" (as is the case for 3" PVC pipe) it's actually about 3.25" in diameter. Huh? A 2.5" pipe should have an outer diameter of 2.875" and a 3" has an O.D. of 3.5". What kind of pipe has an O.D. of 3.25"?

    Has anyone ever seen a cast iron pipe in between a 2.5" and a 3" size? How can I splice in a replacement if it's not a standard size?

  2. #2
    Moderator & Master Plumber hj's Avatar
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    A thin wall section of 3" pipe will have a smaller o.d. You probably have SV cast iron pipe, especially if it is bell and spigot. Cast iron pipe is NOT sch. 40 so it does not conform to the standard dimensions. They maintain the 3" i.d. and let the o.d. fall where it may depending on the wall thickness.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    They make banded couplings to fit the two different dimmensions, but you may have to go to a plumbing supply store to find one. Also, I've read that in some places, it is illegal to splice PVC in between CI runs. CI is quite heavy, and if not properly supported, could damage the pvc. Other than that, functionally, it should work. You'll notice that the pvc will be noisier - you'll hear the water flowing down the drain much more than in the CI. You might want to just buy a section of hubless CI to replace it.
    Jim DeBruycker
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    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member pronouncedeyen's Avatar
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    Yikes! So how can you splice in a piece of PVC and a fernco if the O.D. is not the normal 3.5" diameter? Or do I need to somehow repair the cast iron pipe with putty and/or epoxy?

  5. #5
    DIY Senior Member Fubar411's Avatar
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    You're ok, just figure out the true OD of the pipe you have and go to a real plumbing supply store. Also pick up some clamps from the supply store to support your pipes above the PVC, so the PVC isn't carrying the load.

  6. #6
    In the Trades Gary Swart's Avatar
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    If your are going the splice in PVC route, you must use banded couplers, not just plain neoprene sleeves that have a hose clamp on each end. Band couplers are similar, but they have a band over the entire sleeve.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    As I and others have said, they do make banded (no-hub) connectors to fit two different OD diameter pipes together (they both would have the same ID)...it's just that I've not seen them stocked in a big box store...they only carry a small selection of what's available.

    If you don't support the CI before you cut it out, things could shift. CI is VERY heavy, and if not properly supported, cutting out a section can be both dangerous and problematic.
    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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    General Engineering Contractor ballvalve's Avatar
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    If you have good access to the pipe and need it fixed fast, wire brush it and tap on it to find ALL the thin spots. [If its all thin, forget the following]

    Sanding dilligently at the holes, then fiberglass tape embedded in good epoxy over them will keep you good for a long time. Or neoprene gasket with hose clamp and backer.

    That would give you time to find the fittings you need or get the house sold.

    I suppose the plumbers here would take issue with that farmers fix, however. With good technique, it can be a quick and effective repair.

    If he does not have the skills and money to do it "right" way, epoxy is better than a botched iron and fernco job.

    I have a perforated brass sink trap that I wrapped in glass tape and epoxy 20 years ago here that looks like it will go until the nuts rot off too. It was a rainy Sunday and the stores were closed.
    Last edited by ballvalve; 10-07-2010 at 01:51 PM.

  9. #9
    DIY Member pronouncedeyen's Avatar
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    Jim: I went to a pretty big plumbing supply house here and they had never heard of a cast iron pipe 3.25" in diameter so they didn't have a no-hub connector to fit it. The person there said I might be able to use one of the kind that has 2 hose clamps and a metal band around the whole thing and really squeeze it down. He thought since it's a waste pipe I might be able to get away with it. I'm thinking that the top one will work because it goes from CI (larger OD) to PVC (smaller OD) but because the bottom coupling will connect a larger PVC pipe to a slightly smaller CI pipe that it will eventually leak. Maybe I should bite the bullet and remove everything back to the standard 3" bell and spigot connection and replace the lead/oakum with a neoprene sleeve.

    How hard is it to take apart an lead & oakum connection without breaking the fitting?

  10. #10
    Master Plumber Redwood's Avatar
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    Quote Originally Posted by ballvalve View Post
    If you have good access to the pipe and need it fixed fast, wire brush it and tap on it to find ALL the thin spots. [If its all thin, forget the following]

    Sanding dilligently at the holes, then fiberglass tape embedded in good epoxy over them will keep you good for a long time. Or neoprene gasket with hose clamp and backer.

    That would give you time to find the fittings you need or get the house sold.

    I suppose the plumbers here would take issue with that farmers fix, however. With good technique, it can be a quick and effective repair.

    If he does not have the skills and money to do it "right" way, epoxy is better than a botched iron and fernco job.

    I have a perforated brass sink trap that I wrapped in glass tape and epoxy 20 years ago here that looks like it will go until the nuts rot off too. It was a rainy Sunday and the stores were closed.
    You are right some of us would take exception to it....


  11. #11
    Master Plumber-Gas Fitter shacko's Avatar
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    ballvalve:

    If you are an electrician I get cold shivers to think what you may have hooked up on someones' wires; duct tape comes to mind!

  12. #12
    In the Trades Gary Swart's Avatar
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    As a lifelong DIY, I hate to give this advice, but I think you are into something that is beyond your experience and knowledge to deal with. At best, the fixes that have been suggested even if done reasonable well are real hack jobs and will not hold up long. In addition, if you start cutting cast iron pipe, you run the risk of serious bodily injury if you err on provided sufficient support. There are times when the wise DIYer call for help. I think this is one of them.

  13. #13
    Master Plumber-Gas Fitter shacko's Avatar
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    Quote Originally Posted by pronouncedeyen View Post
    Yikes! So how can you splice in a piece of PVC and a fernco if the O.D. is not the normal 3.5" diameter? Or do I need to somehow repair the cast iron pipe with putty and/or epoxy?
    This is what you need, it is made by Fernco;



    the number is 3000-4

  14. #14
    DIY Member pronouncedeyen's Avatar
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    Quote Originally Posted by shacko View Post
    This is what you need, it is made by Fernco;



    the number is 3000-4
    Shacko: I don't see that model number on the Fernco page at http://www.fernco.com/plumbing/shiel...flex-couplings . Did you mean 3000-44? What is the advantage to using the ProFlex line over a regular Fernco coupling?

  15. #15
    Master Plumber-Gas Fitter shacko's Avatar
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    The ProFlex is a banded coupling, a regular Fernco just has two hose clamps on it, the ProFlex is designed to go between two different size pipes, that number comes from their spec. sheets. It supposed to be 3000-44, A Mission Coupling (different brand) is a number 44.
    Last edited by shacko; 10-07-2010 at 03:56 PM.

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