Cut Cast Iron Elbow To 40mm Waste Pipe Connection

[MrMiller]

Good Evening All

I have a problem with a leaking old lead pipe feeding from our bathroom to cast iron downpipe which I previous posted about here:-

Leak From Bathroom Sink / Bath Waste Coming Underneath Old External Wall Cast Iron Joint

Good Afternoon Folks I have a tricky issue here which I am hoping someone may be able to offer some advice / recommendations with:- We have a leak which has developed somewhere in the piping between our upstairs bathroom and the joint to the old cast iron elbow (? sorry, think that's the term)...

www.diynot.com

I got some good advice re trying to remove the pipe from the bathroom side first and where to cut the cast iron branch in order to join some 40mm pvc waste pipe, which I hope to replace the lead pipe from the bathroom with.

Anyway, I ordered some carbide blades for my reciprocating saw but in the meantime I was thinking about the join on to the cast iron again and the best approach. The funny thing is that I noticed one of my neighbours appears to have had exactly the same issue at some point in the past:-

Lucky for them, they don't have an extension making it an internal issue but you can see they've done the same thing and cut the cast iron back and now have a smaller pipe coming from their bathroom, with some kind of mortar repair around where they must have bust the branch off the wall.

My question is - What kind of join have they got in place here? As a complete layman it looks like something has been set into the cast iron side and held in place with some kind of putty / sealant but I guess its got to be something better than that?

But anyway, given that's the exact kind of join I need to make, does anyone have any suggestions of anything more modern than this which would be better?

Best I can think is something like this:-

https://www.diy.com/departments/adaptor-coupling-mac-0633-53mm-63mm-to-40mm-50mm-flexible-rubber-boot-reducer-coupling-adaptor-pipe-connector-joiner/5060841422985_BQ.prd

But I'm not sure if that's a great thing given the downward flow of water from the smaller side of the connection to the larger...

Thanks for reading and I'd be gratefully for any advice anyone may have.

 

[Madrab]

All they did was cut the cast flush with the socket - inserted a plastic coupler into the cast that was left in the socket and then sealed that in using whatever they used, can't tell from that photo what it may be, could be a number of things. Then just connected up an elbow and waste pipe into that.

Silicone adhesive is a good medium to use, something like wet grab or a similar polymer, I've used that to join plastic to obscure cast pipe sizes and it's worked well but you need to be able to get into the cast and make sure it's all clean and rust free and ready to take the adhesive properly, that may not be easy to do in your case.

 

[MrMiller]

All they did was cut the cast flush with the socket - inserted a plastic coupler into the cast that was left in the socket and then sealed that in using whatever they used, can't tell from that photo what it may be, could be a number of things. Then just connected up an elbow and waste pipe into that.

Silicone adhesive is a good medium to use, something like wet grab or a similar polymer, I've used that to join plastic to obscure cast pipe sizes and it's worked well but you need to be able to get into the cast and make sure it's all clean and rust free and ready to take the adhesive properly, that may not be easy to do in your case.

Thanks Rob. Do you think doing it like that or using some kind of bung would be a better approach?

I was thinking I must be able to get some kind of rubber adapter for 40mm pipes which I could push down snuggly inside the cast iron. I'm not sure if I would seal around that or whether even it's wise to incase it causes the rubber to perish. But if I could do that then with the 40mm in place there, I'd just be cutting and solvent welding back to an elbow and then the piping from the bathroom itself. The water is always coming down the way so there'd never be any pressure against a rubber adapter if it was "jammed" appropriately.

Thanks.

 

[Madrab]

The key here really is sealing in the connection, however that may be performed. Leaving a stub of pipe allows a fernco/flexi seal type reducing coupler to be used, that removes any requirements to have sealants or similar to ensure the join doesn't leak, as it uses a S/Steel banded mechanical rubber seal.

The trouble with using sealants or other types of mediums like those are unless it is prepped really well, longer term they can cause problems, especially with cast, as it ages and invariably rusts that seal can be compromised, come loose or if the pipe backs up then it can leak badly if not right.

 

[Hugh Jaleak]

If the Cast socket is clean I'd try a McAlpine DC-1 into the socket, see how snugly that fits. If that'll give you a decent seal, then a 110 to 40mm adaptor into that.

 

[MrMiller]

If the Cast socket is clean I'd try a McAlpine DC-1 into the socket, see how snugly that fits. If that'll give you a decent seal, then a 110 to 40mm adaptor into that.

Thanks Hugh. I think I get what you're saying there but I think that would mean putting that DC-1 connector over the cast iron pipe after I'd cut it.

Not sure if you if you seen my previous post but I'm looking at making a cut in the cast iron branch about here:-

So I probably won't be on a clean join for connecting over the top. Plus I guess I'm not sure what the exact width will be there.

I wondered if something like this:-

https://www.screwfix.com/p/mcalpine-drain-connector-black-32-40mm/3502V

pushed in there would work, with the 40mm coming in angled down from the left hand side where it'd be joined to the replacement 40mm elbow / bend at the replacement bathroom exit pipe.

 

[Madrab]

No - the DC1 would normally fit inside a 4" cast pipe more, which is likely to be the size of the main soil downpipe in the pic, rather than, what looks like it may be a 3" horizontal cast pipe in the pic. Again, the linked to screwfix part is for a 4" pipe.

 

[MrMiller]

No - the DC1 would normally fit inside a 4" cast pipe more, which is likely to be the size of the main soil downpipe in the pic, rather than, what looks like it may be a 3" horizontal cast pipe in the pic. Again, the linked to screwfix part is for a 4" pipe.

Thanks Rob - Yes, you're right, I was imagining that DC1 connector completely the wrong way around. And yes, I think the cast iron is more like 3 inches rather than 4. Anyway, assuming I can get something similar for 3 inches, I think I'm looking at something like this:-

Is that right? If that works it would be great as all water flow would be going down further into the next piece and it doesn't look like I'd need to do any sealant around the cast iron connection if all tight enough...

 

[Hugh Jaleak]

I didn't realise you had 3" Cast Pipework, my apologies. Makes it somewhat more awkward to find something that'll fit, 'off the shelf', as 3" seems to be in the realms of the more specialist fittings. Might work with an appropriate sized Flexseal (Fernco) Coupling, they do a 75-90mm reducing to 50-64mm, then reduce 50mm waste down to 40 as required. https://www.pipekit.co.uk/products/fernco-adptor-coupling-30-35-38-43mm?variant=55239007928699

 

[MrMiller]

I didn't realise you had 3" Cast Pipework, my apologies. Makes it somewhat more awkward to find something that'll fit, 'off the shelf', as 3" seems to be in the realms of the more specialist fittings. Might work with an appropriate sized Flexseal (Fernco) Coupling, they do a 75-90mm reducing to 50-64mm, then reduce 50mm waste down to 40 as required. https://www.pipekit.co.uk/products/fernco-adptor-coupling-30-35-38-43mm?variant=55239007928699

No worries - Actually, as soon as I'd sketched that out and wrote that I thought it was 3" I starting thinking - hang on! Best I could find was some guy on a screwfix forum saying he was going to cut the fins off and go for it anyway!

I was looking at those Fernco ones as well. Maybe it would be okay but would be securing on the outside. Would worry about hot bathwater always coming down through that with it being in a boxed in spot as well.

Maybe something like this:- https://www.ebay.co.uk/itm/365769455108 is the answer. But then 1.5 inch not exactly 40mm but maybe it is when talking pipes?

 

[Madrab]

Maybe it would be okay but would be securing on the outside.

That is exactly what they are designed for and they provide a very secure, watertight seal. Used them many times as transition couplers from cast to plastic in many different situations, they are considered a tried and trusted standard for exactly what you are trying to do.
Bung type rubber adapters are more likely to leak longer term, they are notorious for it, especially, as I mentioned, once the cast inevitably rusts over time. They do run inside the pipe rather than outside, so I see where your thinking is going, it would even work with just the plastic pipe inserted into the cut cast and then sealing it up all the way around though that would be a fudge. Honestly I've seen more leaks appear from those rubber type bungs or fudges into boss branches and cast pipe than any other adaptation.
As suggested if you could cut the cast and then get into the pipe and really grind it clean and then seal it up prior to fitting and then seal around it properly then it may last long term but give the position and space you have, I would think that would be really really difficult and if any time it was to back up then you could have a real mess on your hands if it blew out.

I would also consider creating an access to that stack for rodding/servicing purposes if needed in the future.

 

[MrMiller]

Thanks Rab. If that's expert opinion I'm happy to go with that. Only thing is with this being a reducer, I guess the rubber can't be sheathed / banded which - again, no expert myself - I'm sure I'd read was favourable.

... I would also consider creating an access to that stack for rodding/servicing purposes if needed in the future.

That's another story in itself! Really the whole stack should have moved to the back of the house - rather than left on the side - when the extension was done...

 

[Madrab]

Only thing is with this being a reducer, I guess the rubber can't be sheathed / banded

Not quite sure what you mean by that? Are you talking about the ribs that are on the DC1 that then run inside the pipe?

As long as the outside of the cast is nice and clean from corrosion and peeling paint etc, the jubilee band that the flexi seals use provide a very strong grip and seal on the pipe, to the point where it will hold a connection that becomes full of water, say from a blocked soil pipe that backs up, quite happily without giving way.

 

[MrMiller]

Not quite sure what you mean by that? Are you talking about the ribs that are on the DC1 that then run inside the pipe?

I just meant that if I went with a Fernco adapter such as the one Hugh had linked to above, ie. https://www.pipekit.co.uk/products/fernco-adptor-coupling-30-35-38-43mm?variant=55239007928699 (which is pretty similar to the B&Q EPDM one I linked to in the OP) then it can't be stainless steel banded like a non reducing coupler like this one:-

https://www.onbuy.com/gb/p/fernco-p1056-33rc-3-in-pvc-and-cast-iron-flexible-shear-banded-coupling-universal-pipe~p123241048/?exta=gshp&extac=gshpfa

Maybe I should just get one of these and connect the cast iron to that on one side and a 3" to 40mm pvc reducer on the other.

 

[Madrab]

Ah ok - All the fernco adapters use S/S jubilee bands but the one you linked to has an additional shear band.

Shear bands can be used on straight couplers but not on reducing couplers due to their shape. Your application wouldn't really need any shear protection as it shouldn't be experiencing any significant lateral loads nor should there be any danger of the vertical cast slipping down putting load onto the coupler.
The one @Hugh Jaleak linked to should be all you need, don't forget to check the diameter of the cast first