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Thread: Easiest way to deal with a corroded drain at floor slab?

  1. #1

    Default Easiest way to deal with a corroded drain at floor slab?

    Our house was originally constructed in 1957 with a mix of galvanized and cast iron for drain pipes. In 1970 the previous owner did some remodeling and used copper drain pipes. Now it's our turn to remodel...

    The photo below shows the drain pipes from our bathrooms and laundry room. We believe the drain pipe under the slab is cast iron, with a cast iron hub at the floor slab. There's a copper drain pipe tying into that CI hub - you can see the corrosion where the metals meet.

    Our replacement drain pipes will be PVC.

    Can we cut the copper below the T, leaving a 2-inch stub of copper, and tie our PVC drain into the copper with a Fernco fitting? Or do we need to bust out part of the concrete slab and tie the PVC into the CI below the slab (so as to remove that corroded hub?)

    Thanks for any advice or ideas you can provide.

    Drain assembly, looking east

    Close-up of corrosion, looking east

    Close-up of corrosion, looking west

  2. #2
    Plumber patrick88's Avatar
    Join Date
    Sep 2007
    Webster Ma.


    You could cut it at 2" above the cast iron. The thing to remember is that the cast Iron is really old. I would assume it is rotting under the floor. I have removed cast iron younger than yours that is so rotted it has split causing a clogged drain. It would be so much better to just dig it up and replace all the cast iron and replace all the galvi. This way you will never have any problems for years to come.
    I'm just starting to work with an old friend of mine to bring solar electric and hot water systems, wind turbines, Flex Fuel Boilers, batteries, hydroponic gardening, books, pellet grills and more. Also the parts for DIY installation.

  3. #3
    Master Plumber master plumber mark's Avatar
    Join Date
    Feb 2005
    indianapolis indiana - land of the free, home of the brave....
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    Talking the fernco fitting

    The fernco will probably work....

    when you cut the copper you will know the status of
    how bad it is...

    it might just be easier to chisel out the lead and simply install the 2 inch PVC directly into that cast iron hub

    I would not fool with anything under the floor..

  4. #4
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default joint

    Why would you want to make a connection to the only part that shows corrosion? The hub is at the floor so just remove the copper from it and make whatever connection you are comfortable with into the hub. I would pour a lead/oakum joint with a stub of cast iron, but others would do it differently.


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