While removing the toilet the The previous flange came off with it. We suspect that is what was causing a leaking issue on the ceiling below. So we went to replace it with an extender flange but the 4 inch extender flange is not getting a tight seal on the cast iron pipe. What are my options?
It sounds like you can get at the pipe from below. I would highly suggest cutting some of the cast iron away and using a rubber gasket coupling (i.e. a Fernco) to transition to PVC. Then you can put a regular PVC pipe flange up there and avoid the problem of depth entirely.
Open the Floor from rafter to rafter(circular saw). That gives you access to the area you are working on. Later you cover that area with a piece of plywood of the same thickness and support the piece with the existing rafters and some sistered in 2x4's.
I bet the old cast iron is laying on the ceiling below and that's why you don't get a tight seal. Support and lift the cast iron a bit up that you get the right heights. That will give you the seal. The key is that you really see what you are dealing with. Good luck.
They have toilet flanges that are longer then the one in your photo. Yours looks like four inches. The one pictured below is 6 inches long and might be long enough to solve your problem.
You'll probably need to go to a plumbing supply store to get one. Good luck.
That style of PVC flange will not provide a good seal to the cast iron hub below. Originally, the flange would have been cast iron and was connected to the soil pipe using a combination of lead and oakum, which is a hemp fiber. The oakum would be packed in around the fitting, and lead solder would get ladled over the top to make it water proof. The purpose of the oakum was to prevent the solder from falling through the gap in the pipe before it solidified. The original flange must have been removed as part of a bathroom remodel at some point.
Using lead and oakum is still used occasionally, but many installers have switched over to hubless fittings, which are connected by a type of coupling known by the brand name Fernco. To install the new one, use a reciprocating saw to cut the bell off the end of the cast iron pipe and use a piece of PVC pipe the same diameter to extend it to the proper length. Once that part is done, you can then install a standard toilet flange, and it should not ever leak again.
