Replacing cast iron waste with plastic

[curium]

Hi,

I'm having a loft conversion done and I'm considering replacing the cast iron waste pipe while the scaffolding is up as this will allow it to be taken down from the top which should make the weight more manageable.

The cast iron waste is only connected to a single toilet currently and then extends up to the roof line to vent - presumably this will have to be extended to go past the new dormer. We're putting another toilet in the loft conversion so would have to connect to it or its replacement.

My question is about the bottom of the pipe. It enters the ground in my back garden and the pipe has been concreted around in order to blend in with the concrete slabs in the garden.

I'm not bothered about the garden slabs. What I want to know is should I break up the concrete in order to remove the cast iron at the point that it enters the clay pipe or should I cut the cast iron above ground and then find some kind of robust connection to connect the cast iron stub to plastic?

Thanks

 

[Mottie]

or should I cut the cast iron above ground and then find some kind of robust connection to connect the cast iron stub to plastic?

I had that done years ago. Someone on here called it a 'timesaver' connection. A metal clamp that fitted the cast iron pipe on one side with the plastic pipe on the other.

 

[Madrab]

Is the cast damaged or in poor condition? Just wondering the reason for removing it?

If you are removing to below ground level then it would normally be cut down as low as possible to remove the corrosion risk of any cut cast left in the ground, so down at the clay level and if it's standard diameter then use a transition coupler - something like a McAlpine DC1

 

[Hugh Jaleak]

If you're renewing it, I'd do the lot. Invariably the joints between the cast and clay drain at the base of the stack are past their best, with many found to be broken and leaking, as there's no flexibility in the old pipework to allow for movement.

 

[curium]

Thanks all. Builder is wary of disturbing the join with the clay pipe in the ground so we’ve decided to remove it from the bend at 1st floor level and then replace with plastic up to the loft level.

 

[johnny2007]

I replaced a couple of them in my time.
The internal bore had gone from 3.5 inch to less than a couple of inches and I wondered how they were still draining.
At the same time I removed some plastic 4 inch pipes and apart from little debris, they were still perfect.
That's one application where plastic works very well imo.
It's a bit of a pain to remove cast iron bends entering the wall, but it pays off in the long terms if you ask me.