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Cutting/Disconnecting and Plugging 4" Cast Iron Drain Line

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  • Cutting/Disconnecting and Plugging 4" Cast Iron Drain Line

    Originally posted 2-17-2017 2:45 PM
    By: Logcabin1

    I would really appreciate some advice here, as I'm a little over my head but really want to complete this task correctly.

    I have installed a new bathroom suite as a small addition to my master bedroom and now need to demo the old bathroom which will become a walk-in closet.

    The bathroom to be demo'd is the original to the 1929 log home and the waste pipe is 4" cast iron with oakum/lead filled joints.

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    The bathroom is on the first floor and I have access to the drain pipe in the tall-crawl basement. In the photo above, you can see the 90 elbow directly beneath the toilet as well as a 1 1/2" PVC drain line entering the next section downstream of the elbow. The 1 1/2" PVC drains the tub and sink in the same bathroom so I will be cutting and plugging that pipe as well but would like to preserve the ability to tie into that inlet to the DWV here sometime in the future. So, I would like to cut and plug the cast iron pipe either by removing the oakum/lead joint or, if I will have enough room to plug properly, by cutting the cast iron pipe just to the right of the junction. In other words, I would like to leave the cast iron segment that includes the 1 1/2" inlet in place.

    I've read that the oakum/lead joint can be removed with great patience and effort (I do have a map gas torch but nothing more specialized, nor do I have a gas mask for lead vapor). I understand that another option is to break/cut the pipe using a chain-type cutting device that may be able to be rented (need to confirm that) or a saw-zaw, preferably with a special diamond blade, or even with a metal cutting wheel on a grinder.

    If I break/cut the pipe just to the right of the seam will I have enough straight pipe available to cap it? What is the most appropriate capping method? I have read online that the best way to plug it is to use a NO-HUB coupling and cast iron blind plug but I'm not sure what that would look like.

    I will appreciate any input on solving this challenge.

    Thanks Eric (aka Logcabin1)

  • #2
    Originally posted 2-18-2017 8:41 AM

    If you can pull the elbow out of the bell end you can use a rubber donut to attach a PVC clean out. Home Depot carries them.

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    • #3
      Originally posted 2-18-2017 9:48 AM
      By: Logcabin1

      Thanks for the response chrisb.

      The operable word appears to be "If."

      Have you ever tried to break one of these oakum/lead seams? How did you do it? Did it require specialized torch and breathing device or were you able to gouge filler out of the annular space inside the "bell" end without damaging the iron pipe? Will I be able to torque the elbow (after cutting the top section) without inadvertently compromising the seam at the next downstream coupling? What precautions should I make?

      My dilemma is whether or not to attack that seam. I'm concerned that I may get myself 2 hours into maiming the heck out of that seal only to determine that i should have left that point alone and cut the pipe -- but now that I've trashed the integrity of the seal, there is no turning back.

      To remove that seam should I try gouging it out with a screw driver and hammer? drilling it out with which what kind of bit(s)? dremel it out? heat it lightly?

      Can I be near 100% certain that I can break this seal successfully? Back to that operable word....IF

      Eric (aka Logcabin1)


      • #4
        Originally posted 2-18-2017 3:46 PM

        I have not done it in a very long time. I would start at the top and disconnect the flange from the floor. It is probably screwed down. Then just start wiggling and twisting. I think it will just come apart.

        Or just take a Big F hammer and smash on the elbow. I can't see the rest of the pipe. You might need some support to hold it up after or maybe before.

        You can also cut it with a sawsall with the proper blade.


        • #5
          Originally posted 2-18-2017 11:39 PM

          also look at Fernco fittings (the no hub rubber coupler). See how much pipe wall they need to seal. You may want to cut to the left of that 2" PVC so you have more cast iron wall to couple to. Then, transition to PVC or ABC and tie in the 2" pipe and put a 4" threaded female fitting and a plug in the end for clean out access. Make sure you're using drain fittings and not pressurized water fittings -- the elbows are larger radius on drain fittings.

          I've never messed with cast iron, but they do make abrasive saws all blades for cast iron. I have no idea how easy it is to twist apart or unsolder.
          Kent, WA


          • #6
            Originally posted 2-20-2017 12:01 PM
            By: Logcabin1

            Thanks for the ideas chrisb and suemark.

            Turns out couldn't wiggle the fitting beneath the toilet as the T&G flooring had been installed around the flange tightly. Decided to cut and cap after looking at Fernco options.

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            Used large grinder/metal cutting disk to cut nearly all the way through.

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            Used a chisel to break the last bit because I was concerned that once I cut through I may pinch the blade, potentially chattering the relatively fragile disk.

            Overall success - will post final photo but ran out of allowable file size/space. If I could redo the operation I would use a marker to set the cut line. The large grinder I was using made it difficult to see exactly where i was to cut by eye - I would have preferred leaving another half inch to fasten the Fernco cap onto. I had a little more meat available before the bend. Also, rather than using a chisel for the final break I would insert a wood shim and move to the far side with a smaller 4 inch grinder to make the final cut. The break was not as clean I would have liked but still left plenty of pipe for the hose clamp to grab.

            Eric (aka Logcabin1)
            Attached Files
            Last edited by TransferGuy; 04-02-2019, 07:21 AM.


            • #7
              Originally posted 2-20-2017 12:25 PM
              By: Logcabin1

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              Once I had the first cut made down in the basement I had a friend push the pipe up through the floor to give me space to cut beneath the flange so I could remove the pipe.

              Eric (aka Logcabin1)


              • #8
                Originally posted 2-20-2017 1:22 PM

                looks good. Nice job.