On 2012-07-03 21:35:07 +0000, fred said:

Agree it is likely cast iron, I have seen one with a similar collar
from a 60's build, the collar was sealed using lead wool compacted with
an offset compacter/chisel type tool.

I'm still not sure. Other than a magnet, is there a test?

I'd cut it off 2" or so from the wall to get a lower entry and use a
flexible pan connector to mate with the inside of the pipe. They're
meant to be self sealing but I'd add sanitary silicone to the
compressible vanes to make sure.

That's pretty much what I had in mind. How far down the pipe would you
aim to get the flexible connector? Does further = better? I suppose
there's a danger it won't seal properly if it's halfway round a bend
instead of in a straight section.

No need to disturb a cast iron stack in good condition, it should last
a century. Hopefully the building is not 99yrs old ;-).

Probably about 120! But I suspect the first bathroom was installed in
the 1930s...

Thanks for the advice.

--
James