Cutting 4" CI Sewer Pipe

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  • This topic has 3 replies, 3 voices, and was last updated 9 years ago by nicktheplumber.
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    • #280021
      Gilbert Chacon

      I need to remove a leaking 5 foot section of 4 inch cast-iron sewer pipe in my basement and replace it with 4 inch pvc schedule 40 sewer pipe. If I use a snap-cutter or a Sawzall to cut the CI pipe do I need to support the section I’m cutting out? What about the CI sections that remain?

      I understand from reading the postings that 2 Fernco 4″ CI 4″ coupling are the best choice for connecting the PVC pipe to the cast-iron pipe. Is that correct?

      Thanks for your help


    • #302066


      –4″ CI pipe is heavy, and a stack going up through your roof can weigh hundreds of pounds. If you are cutting into a vertical stack, you should support the pipe above and below where you will make the cuts.The pipe should already have been supported at several points when it was installed, but you don’t want it to move when you cut it. The 5 foot cut out section will be hefty but you should be able to manhandle it. If it’s vertical or slanted, make the lower cut first and then the opper. If it’s horizontal, support the middle with a cable or rope before you cut it out.

      –If you are slicing in a section of no-hub CI, you can use 4″ Mission/Fernco no-hub connectors. If you are splicing in 4″ plastic pipe you need to use special transition couplers, such as the Fernco Proflex. The Proflex couplers have a smooth solid SS band 9as opposed to the corrugated no-hub coupler band, along with a beefier rubber gasket. This is needed to accomodate the slightly different ODs of plastic and CI pipe.     

    • #302068

      Thanks Nick. The section of the CI pipe I need to replace is horizonal.
      I’ll definitely support it before I cut it. Do you think I could cut the CI pipe with a reciprocating saw? I’ve read it takes longer but there is less chance of breaking the good sections of the pipe that are at both ends of the section I am removing.


    • #302069


      You can cut 4″ CI with the Sawzall, but you will go through several blades doing it. I almost always use my Ridgid snap cutters for this sort of job, cause it’s quick and easy. I reserve the Sawzall for those really close-quarters cases where I can’t get the chain around the pipe with my close-quarters Ridgid cutter.

      It’s possible to crack old corroded CI with a snap cutter, but it’s more of an issue with fragile “corked” clay pipe than CI, and it is more of a problem with horizontal runs that tend to remain wet. I can’t say that I’ve never cracked up a CI pipe with the snap cutter, but when I did the pipe was already shot and more of it needed to be replaced than the section I was splicing into.

      Unless you’ve had experience and know the “feel” of a snap-cutter on CI, you’d do better with the Sawzall. A word of caution: the Sawzall vibrates a lot and is not guaranteed to not crack a weak pipe. You can minimize the risk by going slowly, letting the saw do the cutting without apply too much pressure, and replacing the blades when they get dull.

      Good luck,


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