I was planning on adding a donut to the cast iron hub, but when I was removing the lead seal, the hub broke off entirely. Now I have a broken off 2 inch cast iron pipe right beneath the slab. How do I go about connecting the pvc to this? I was thinking of just using a compression fitting now. Thoughts?enter image description here

  • If it can be 1-1/2" you may get extremely lucky and find a weird grommet that goes inside 2" cast iron ID. Otherwise you bust it up until you find a hub. Or....? +1
    – Mazura
    Commented Feb 27, 2022 at 10:02
  • 1
    Can the PVC pipe fit inside the cast iron pipe?
    – bobflux
    Commented Aug 5, 2022 at 10:36
  • 1
    Stupid question: What sort of fluid flows through this pipe?
    – Hot Licks
    Commented Oct 19, 2022 at 20:20

4 Answers 4


A few more details would be helpful. How far does it go straight down after the surface of the concrete? Where is it going above the concrete? As in is it straight up to a drain? Or up to the next floor? Is it a vent pipe? Or a drain? Or water supply? You mentioned lead seal, so I guess a drain pipe or vent.

PVC 2" should be the same outer diameter as the cast iron. You get one of those rubber couplings. Half of the coupling on the iron, and half on the PVC. I did something similar with 3" after cutting/breaking up my concrete floor in the basement, but that was horizontal. Then put the concrete back over it.

You need to remove enough concrete to allow you to tighten the hose clamps that tighten the rubber boot to the pipes. Use some sandpaper to make the outside of the cast iron smooth for the rubber boot. Some plumbers grease will also help slide the boot over the pipes more easily.

Why did it break? Just something to think about to prevent the repair from failing.


Your gonna have to bust out that concrete around the cast iron enough where you can get a rubber boot that will go on and rubber boot to pvc.

  • 1
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    – Community Bot
    Commented Mar 8, 2022 at 7:42

A compression fitting could work. Just be sure to remove enough of the concrete to get a good, solid connect onto the cast iron pipe. Thats the most important thing.

Without a solid connection, it could come off or loose and you will have to jack hammer the concrete back up and start over again.


Since this is 2", I'm pretty confident that this is not for a toilet. You could see how tight an 1.5" PVC pipe will fit. If loose, try a 2". If the 2" fits fairly tight, you could glue a 2" to 1.5" adapter onto your new 1.5" PVC pipe. Clean out the iron pipe as best as you can. If it's rough, that's fine. See if the 2" adapter will fit inside of the iron pipe. This should be pretty tight. Take a heat gun and warm up the 2" adapter until it starts getting pliable. Jam it into the 2" iron pipe and hold in place. Give it a minute to cool and see if that will hold. If this doesn't work, take your assembly dampen it and the iron and apply Gorilla glue liberally, then stuff the 2" adapter back in and secure. The Gorilla glue will expand to fill any gaps. The stuff will stick to almost anything. It should fix you up without hammering out the floor.

  • Welcome to Home Improvement! A) Formatting, formatting, formatting! It makes an answer readable. B) There are a variety of "Gorilla glues" available, specifying which one would be most helpful. C) "dampen it and the iron" what iron? Where did that come from? D) Does a heat/friction fit like this qualify as a code compliant installation? If so, please cite the code that allows it. It sounds like this has a very significant chance of leaking, so it would be good to know that it is code legal & would pass an inspection.
    – FreeMan
    Commented Jan 25, 2023 at 14:54

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