I have an old home built in the 50s and the sewer system appears to be cast iron, I am in the middle of a kitchen remodel and noticed a badly rusted kitchen drain pipe, well today I was under the house and noticed the kitchen drain pipe that was rusted had busted in too. I have cut back the rusty cast iron pipe and used a ruber coupler to redo the plumbing in ABS from the ground up. The nube that I cut back goes into the ground in the cast iron main. My question is that the old cast iron that I cut out is very large 2 1/2 - 3 in in diamiter (outside) the pipe that I cut back appears in bad shape, I cut an additional 2 in out and the the thickness of good metal is very thin in places (thickness of a quarter to 1/4 in. Although the 2 in peice I cut out stans up to hammer blows I am worried that if I leave it as is it won't last another 10 - 20 years. Whan looking at the pipe I cut out it's pealing in layers like an onion. Should I cut the section out at the main or leave it like it is? I have never seen cast iron do this?
I agree with Mike... Replace as much as you can now... PVC is cheap....
I replaced some cast iron under a floor [of course it was concrete] one time after it had a groove cut clean thru it from the sink downflow.
Thought I could cut it back to good and save it, but it kept breaking off.
This particular pipe was less than 20 years old.
If you can get to it without too much trouble, I would replace it.