I have a big old gawd awful cast iron (at least I think it's cast iron, the house was built in 1940) toilet flange that is in sorry shape.

See? enter image description here

There will never be a better time to replace it - as we have the floor above and ceiling below it open, and it desperately needs it, obviously.

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I have never done anything with cast iron before, however, and do not know how I should proceed. Should I break the pipe back on the long straight stretch and connect to pvc using a rubber connector like this?

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Or should I focus on just trying to replace the flange (which seems much more difficult to me...)

I know cast iron is hard to cut - is a grinder going to be more effective at cutting this stuff? (Huge mess for the kitchen below :( - but I can hang trash bags or something underneath I suppose...)

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UPDATE 5 Nov 2012

The end result:

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  • 1
    If the pipe was corroded enough to truly warrant being replaced then cutting it should be fairly easy I would think :) But I agree it is ALWAYS best to fix stuff like this while the walls and floors are opened up. Commented Oct 29, 2012 at 11:23
  • Does it bend off and go elsewhere in the floor or does it pretty much go straight down? If you can cut it where it goes straight down then you should be able to cut it from the bottom as well and then it will just fall through to the basement. You would be able to replace the WHOLE PIPE with PVC at that point. Commented Oct 29, 2012 at 11:26
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    Like I said - the main stack is fine. It's just the flange that needs replacing. The really poor decision here was what they did to the structure in installing that toilet. I mean - look at that joist! They cut 6" off of it making it a 2x4. Could you imagine that giving way while you're sitting on the john??? Commented Oct 29, 2012 at 11:48
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    I think a toilet flange is the least of your worries right now. I would be figuring out to reinforce that joist. Commented Oct 29, 2012 at 12:00
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    They're both worries and both going to be addressed. :) Commented Oct 29, 2012 at 14:52

3 Answers 3


For cutting the pipe, go rent a chain pipe cutter (aka soil pipe cutter). It will make short work of the pipe and not be too messy. It will make a clean enough edge that a Fernco coupling (like you have a picture of) will work fine.

Obviously you will need to add some strapping to secure the horizontal run of iron pipe if you go this route because you don't want to put any extra strain on that rubber coupling.

I would not mess with trying to remove the flange. I think it will be easier to just cut the pipe.

  • Not that i would endorse it in any way but if you can't cut the pipe it could just be removed from the next flange and then a PVC pipe be inserted and sealed into the old cast iron pipe... or you could just get a push in flange that will sit in the top of the cast iron flange and save yourself the trouble of mucking around with cast pipe. personally I'd be more worried about that gal pipe you have in the wall.
    – UNECS
    Commented Oct 29, 2012 at 10:49
  • @UNECS The gal pipe is already in the process of being replaced. Commented Oct 29, 2012 at 11:47
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    The pipe cutter sounds like the best way to go. I'm not confident that I could successfully remove the pipe from it's joint in a clean, reusable fashion or if I did, that I'd get a good seal to the inserted pvc. We've already had to deal with this toilet leaking onto the kitchen ceiling from the drain, we don't ever want that happening again. And since I clearly have some framing work to do here anyway, I'll be sure to add extra support for the new pipe. Commented Oct 29, 2012 at 11:51

Removing the old pipe

First you want to make sure the section of pipe that will remain, is properly supported (you don't want it falling). Then you'll want to install some temporary supports, to catch the portion of the pipe that you'll be removing.

Use a chain cutter, hammer and cold chisel, or grinder to break the pipe a few inches before the hub on the next pipe. This short YouTube clip shows how easy it is to cut cast iron with a chain cutter.

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Next you'll want to use a hammer and cold chisel to break up the remaining bit of pipe, being careful not to damage the hub. Once you get enough of the pipe broken up, you'll notice a lead ring inside the hub. Using a prybar (or other similar tool), try to deform the ring enough that it can be removed (again, being careful not to damage the hub). carefully drilling holes in the lead ring can make it easier to remove it, just be careful not to drill too deep.

Once you have the old pipe and lead gasket removed, clean the hub up a bit and remove any bits of debris.

Install the new pipe

To install the new pipe, you'll need a 4x4 or 4x3 rubber compression donut.

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Slip the donut gasket over the end of your new PVC pipe, and fit it into the cast iron hub (A bit of gasket lubricant will make fitting the gasket easier). Work the gasket into the hub, until it is firmly seated in the hub.

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Broken hub

If you were a bit overzealous and you ended up breaking the hub, you'll just have to use a coupling to attach the pipes. Cut the cast iron pipe after the hub, then use a coupling to connect the pipe. Make sure both pipes are well supported, since these couplings are not designed to hold weight.

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  • +1 but I would like to add that for extra precautions when using a coupling against cast iron then I would use a liberal amount of plumbers putty around the seams, just in case. This is probably overkill but whatever. Commented Oct 29, 2012 at 12:37

You have used wrong adapter-connector to connect cast iron pipe to ABS/PVC.

Per Code when connecting the ABS or PVC to cast iron you should use No-Hub Adapter fitting. Rubber connector or Flexible Coupling are allowed only under ground.

As defined in the Uniform Plumbing Code section 705.4.2. a mechanical joint shielded coupling for hubless cast-iron pipe and fittings shall have a metallic shield where installed above ground. Flexible rubber couplings with stainless steel clamps, without a shield, are designed for use below ground.

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