plastic to 2" cast iron waste

[maxim naumov]

hello everyone

my bathroom basin's and bath's waste is going into a 2" CI pipe. a 40mm plastic pipe was loosely inserted in a metal pipe that was fixed in the CI socket with lead and some kind of cement. the joint between plastic and metal was wrapped around with some crap (sorry) that kept leaking. I decided to do it nicely, removed the smaller metal pipe and cleaned the CI socket. now it is all nice and clean, but I don't know how to fit a plastic pipe in there properly. I was initially hoping for push-fit adapters, similar to toilet pan connectors that go into cast iron pipes, sealing with fins, but could not find any. one PM suggested putting a rubber adapter that goes onto the outside of the CI pipe and fixed there with a clip, but I could not remove the socket, it is too close to the wall. I cannot replace the whole stack with plastic either.

any suggestions? I read people talking about caulking with some special cement and rope. although this sounds dodgy, I might have no other alternative. could not find the actual caulking compound anywhere though. what's it called properly and can I possibly make it myself?

maybe I could fix the plastic pipe into the cast iron one with silicone sealant and fill the socket around with expanding foam, then plaster/paint?

the pipe's internal diameter is 50mm. the socket's is ~75mm.

thanks very much in advance.

/max

[nightjar]

Get an iron or aluminium hopper that will fit the CI pipe and let the plastic waste discharge freely into that. There is no need for bath and sink waste pipe runs to be sealed, unless they discharge into a soil stack, and the air gap will prevent any tendancy for syphonage to empty the traps.

Colin Bignell

[maxim naumov]

nightjar plastic waste discharge freely into that. There is no need for bath and sink

...but it smells. 8) I'd prefer it all to be sealed. any advice on caulking/rubber adapters? I got a McAlpine caulking ferrule already.

thanks for your reply.

/max

[Vaci]

On Jun 19, 1:15 am, maxim naumov wrote: I was initially hoping for push-fit

A rubber coupling is the preferable, reliable method. The fin-sealing connectors don't seem to seal well in cast iron. I've had a plumber in the past just fit the rubber coupler around the whole lot (socket and all) when they couldn't remove the socket. Some of the couplers have asymmetric ends to join pipes of varying size.

if you are really stuck, Hepworth do a range of "problem solver" plumbing parts which may be of use, otherwise bodging it with (lots of) silicone sealant may actually work - it only has to be sealed, not pressure-resistant.

[John Stumbles]

my 'technique' (if you could thus glorify it) in situations like this is to

1. clean up the inside of the pipe or socket you have to connect into
2. get the nearest size plastic pipe or fitting that fits, building it up if necessary with pieces of plastic pipe slit lengthwise to open up or close down to fit over the end that's going to go into the existing socket so that it's a fairly snug mechanical fit
3. glue it all up with mastic. Nowadays rather than silicone I'd use Toolstation's Stixall (or Evo's Sticks Like Sh*t if I'm rich/out of Stixall). This stuff sticks like, er ... - even to wet surfaces.

[Vaci]

Rubberized bitumen sealant is also very effective - it seems to stick to everything (hands, face, tools, carpet).

[nightjar]

Possibly it does discharge directly into the soil system then.

I would look at fitting a bit of PVC pipe into the socket with mastic and solvent welding adaptors onto that to step down to 40mm waste pipe. 2" PVC pipe is about 60mm OD and 2½" is about 73mm OD.

If you have trouble sourcing short bits of pipe, I have tank nipples in those sizes, which are lengths of Class E PVC pipe 160-165mm long, with a thread cut for about 100-120mm from one end. They are business stock, so I would have to charge and I don't have a price for the nipple without nuts and gasket to hand, but, with postage, the larger should be under £20 and the smaller probably about £10.

Colin Bignell

[maxim naumov]

thanks very much for replies, everyone.

how about inserting the 40mm/50mm PVC pipe deep into the CI pipe, carefully sealing with silicone and then filling up the socket around the PVC pipe with expanding foam to get it a mechanical fix? maybe attach a piece of cardboard with a hole to the socket temporarily to keep the foams density high? or will the foam not stick to cast iron?

I want a solution that lasts. mastic in my experience is very easy to damage, thus loosing the seal. you only need to move/hit the joint once and the seal is broken. it is difficult not to do when you are fitting a sink right above the joint.

regarding push-fit rubber couplers -- can anybody recommend a particular product and where I can get it from?

TIA.

/max

[John Stumbles]

That's why I suggested (a) getting a mechanically snug joint (b) using stixall rather than silicone (though a well-adhered silicone joint can be extremely tough to break: it's just that silicone doesn't always stick well)