So, I just replaced a section of old 4" cast iron pipe with a section of 4" ABS. I used a metal-sleeved no-hub coupling for the connection. I found it surprisingly finicky?? The cast iron was smaller in diameter, which skewed the sleeve to one side when I tightened it, and the rubber sleeve has some visible gaps between it and the CI pipe surface. It is not leaking, but it looks really amateur, and doesn't inspire confidence. Did I do something wrong? Is there a trick to it?

You probably used a plain jane no hub, they make a special one to transition from plastic to cast iron.

You did nothing wrong. It is not too often when both pipe ends are equal diameter. I have tried different methods of 'shimming' the lesser diameter pipe within the coupling but generally, I tighten the larger diameter first as tight as possible keeping the band edges square with the coupling, and then the smaller diameter last. In the end, you've got a stronger joint than a Fernco.

Thanks to both of you! I will see how easily I can get my hands on a CI-to-plastic-specific version. If I can't, I may try again with a new plain one and see if I can do a better-looking job of it.



Edited 1 times.

you can reuse the old one if you can't find a cast to plastic no-hub

i find a 4 band is more forgiving when dealing with differing OD's.

You said "CI to plastics" make sure it's the right kind of plastic. The ones I get from stores here, if they say CI - PL it means to PVC and not ABS.

There is another option besides getting a proper CI to ABS transition coupling where the rubber sleeves account for the diameter difference between the two same nominal size but different actual OD, and that is to put in on the ABS side an ABS to CI no hub adapter. That fitting is glued on to the ABS side, and gives the ABS pipe end the same OD as the CI so you can use a regular no hub CI adapter.



You can get this adapter from our sponsor.

[www.plumbingsupply.com]
[www.plumbingsupply.com]

Aha! Among those options--the wider band, the adapter, the specific coupling--I should be able to put it together much better on my second try. And it's great to know that PlumbingSupply has the adapter available online.

But--"plastic" is only PVC? A Fernco label that says "CI, PL, or ST"--that must also include ABS? Or no?

Yes your no hub coupling will work on ABS pipe. A good trick is to slide your bands over the CI pipe and put your rubber on the CI pipe and roll it inside out and slide your replacement piece in between and un roll it on to the new Abs. you can cut your replacement pipe a little shorter 1/4''on each end. In Massachusetts we must use CI pipe to repair CI.



Edited 1 times.

You need a schedule 40 to "No-Hub" cast iron.