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i want to change my cast outside(app. size 100mm)cast iron waste pipe to plastic i hav been told to remove the cast iron from a collar joint then fit plastic from that point what is the best way to do this.Thankyou

The best way I guess is to get the guy who suggested it to do the work because removing the sealant from a collar is very tricky without breaking the pipe and even if you managed it, I am not convinced the plastic will fit as its diameter is slightly larger than cast iron.

As any joint between different materials will look odd, I suggest you go the extra mile and replace the entire stack.

[quote="plumbbob"]The best way I guess is to get the guy who suggested it to do the work because removing the sealant from a collar is very tricky without breaking the pipe and even if you managed it, I am not convinced the plastic will fit as its diameter is slightly larger than cast iron.

As any joint between different materials will look odd, I suggest you go the extra mile and replace the entire stack.[/q
uote]
thanks plumbbob is there a adaptor from cast iron to plastic

Why do u want to remove the cast pipe? If there is nothing wrong with it then leave it, if it has perished then of course get rid. You can still replace it with a new cast iron pipe, but this is a lot more expensive than plastic and in reality virtually no-one does this as plastic is cheap, readily available and easier to work with. Best solution is to obviously replace the lot as this will look the best (I take it this is external) but you can join plastic to cast iron at any point you like with the correct bandseal. This takes into account the slight difference in diameter between the two materials and is a specially shaped rubber collar tightened by a simple worm drive clamping clip. They don't look all that pretty but it is a quick and easy fix if you don't want to change the whole stack.

bateman wrote:i want to change my cast outside(app. size 100mm)cast iron waste pipe to plastic i hav been told to remove the cast iron from a collar joint then fit plastic from that point what is the best way to do this.Thankyou

I have done quite a few of these. I cut through the cast pipe at about 100mm above ground with an angle grinder,then use 1 of these:-

Google "drainstore.com/110mm-internal-drain-connector-to-soil-stacks-i76.html"

These could be fitted at any height,I just think they look neater if done closer to ground level.

Regards Steve