Coring for a Waste Pipe

[DPM31]

Sorry for some basic questions. I'm moving a whole bunch of stuff around in a bathroom. The cast iron soil stack (4 inch I think) is on the wall directly outside. The existing WC will have to move about 2 metres right. I figure that I can disconnect and rotate the branch fitting outside to pick up the new location which will have to run in cast iron.

I have two questions. Firstly, should the new cast iron pipe be run to the inside - and connect to the PVC inside, or should I run the PVC to the outside and make the union there? The wall is stone and about two feet thick.

Second question relates. If the cast iron has to come inside, what size core should I use? Same question if the union is external? Same question about core size for a shower / basin waste.



Many thanks in advance.

 

[Softus]

Firstly, should the new cast iron pipe be run to the inside - and connect to the PVC inside, or should I run the PVC to the outside and make the union there?

I'd choose the latter - plastic as far as possible.

Second question relates. If the cast iron has to come inside, what size core should I use? Same question if the union is external?

For a snug fit on plastic soil pipe, use 117mm. However, with that wall thickness accuracy will be difficult, so I'd use 127mm.

Same question about core size for a shower / basin waste.

A 46mm core for a snug fit on 40mm pipe, 50mm to give yourself some wiggle room.

If your going through the wall in 50mm, then use something like a 60mm core.

 

[DPM31]

Thanks Softus. Are you suggesting that I should take the PVC out rather than the cast iron in?

Thanks for the advice on the sizes. Wriggle room will be important!

 

[Softus]

I'm not sure that I understand your distinction between 'taking in' and 'taking out', but since I'm advocating the use of plastic instead of cast iron, I suppose the answer to your question has to be "yes".

 

[DPM31]

Sorry, what I meant was should the join between PVC and CI, be inside or outside. I think that the whole would have to be bigger for CI than it would for PVC.