How to seal new plastic soil stack to old cast iron stack

[tonyjeffs]

having installed a gf wc, I'm fitting a new plastic soil stack. The old cast iron stack terminates about 2 foot below ground level, so rather than do it proproperly, and dig out, which could be one hell of a job, i've decided to leave a stub of 6" cast iron pipe protruding above gl. and join the plastic pipe to it.

The plastic sleeve is slightly larger diameter, and-fits snugly over the outside of the cast-iron, There is a 1mm gap to make watertight. Since the cast iron from below ground terminates on the inside, there is a lip, which is liable to catch any falling waste.

What is the best way to seal this junction which won't be accessible again for 50 years , and taper out the lip? What sticks to plastic? Thoughts: Putty mixed with gloss paint; Silicone sealant; grease; Plastic solvent glue, soft rubber fitting with circlips, other?

Brill group!

Thanks, Tony

[R]

Couple of suitable O rings and plenty of Silicon Mastic. Flaunch the base properly with cement

[Dave Plowman (News)]

Go to a decent plumber's merchant and buy the correct coupler for this job.

[Jeff Layman]

If you are really sure you'll never want to get them apart again you could use Isopon or some other similar car body filler from Halfords. Several years ago I had to fit a plastic inspection point to a broken earthenware soil pipe. I used Isopon to build up the break to a level surface, and then more Isopon to fit the plastic to it. Seems to be ok with no leaks.

[mail]

=A0 London SW

It is pointless botching a joint that is not failsafe ie with the plastic inside rather than out Chris

[TMC]

You'll be wanting one of these then