"Steve" wrote in message
...
have you considered just cutting out a section of the iron pipe (with
an
angle grinder) and slipping a length of plastic pipe in its place?
and
then cut the pipe and fit a plastic connector with the facility to fit a
boss.

Thanks for the suggestions. But if I cut the soil pipe, it will mean the
(not inconsiderable) weight of the upper part isn't supported by the lower
part; this will put a lot of stress on the 2 higher supports and on the
outlet from the upstairs toilet. Isn't this a problem ?

If it's as I imagine I think the outlet from the upstairs wc connection will
help support the rest of the stack, but it should have proper supports
anyway. You could always add some more if you think fit (using steel or iron
brackets of course, not plastic).

Whatever the method, I don't want to risk cracking the pipe - presumably
old
cast iron is fairly brittle.

It's brittle to the extent that if you wack it with a hammer it may crack.
Sod's law dictates that it will resolutely refuse to do so if you want it to
and do so too easily if you don't :-)

When I've cut a pipe that was in a corner, using a 4" grinder, I cut halfway
through the pipe at 2 points about a foot apart and sliced lengthways to
remove a sort of rectangular section, then I could get the grinder in to cut
the rest of the way through to the back of the pipe. USE A MASK: the dust
and other stuff that comes of grinding through a soil pipe is outlawed for
use in combat under the Geneva Convention.


--
John Stumbles
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No Rules, OK