Flexible WC connector into cast iron, best practice?

[Madrab]

The real trouble will be how badly corroded the internal section of the cast is, I've seen some real badly corroded messes that need ground back to the metal otherwise they leak like a sieve, hence why the recommendation to line it with a section of pipe first and that would be what's 'glued' into place

 

[denso13]

hence why the recommendation to line it with a section of pipe first and that would be what's 'glued' into place

I have never seen that recommendation and have never had to do it. What are you going to line the cast with and how do you fix it in place?

 

[Madrab]

I have never seen that recommendation and have never had to do it. What are you going to line the cast with and how do you fix it in place?

see post #9 - 3.5" pipe of pipe - grind out the cast so it's as clean as possible then use a piece of 3.5" plastic pipe and use a silicone adhesive to seal the cast and then 'glue' the liner in place. Done it many times where the cast has all to often been chopped and it's been left to corrode internally and then pan connector eventually leaks.

The adhesive (wet grab etc) seals the cast and stops it corroding/breaking down further and the plastic 'liner' then provides a clean surface for the fins of the extension.

 

[denso13]

then use a piece of 3.5" plastic pipe

Where do you get that?

 

[Madrab]

I usually trim down a piece of the soft extension pipe to fit. Trying to remember which of the 4" extensions, might be the macfit, that has fins that can be removed from the end and that inner piece can be used too.

 

[denso13]

I usually trim down a piece of the soft extension pipe to fit. Trying to remember which of the 4" extensions, might be the macfit, that has fins that can be removed from the end and that inner piece can be used too.

Again, I don't doubt you, but I have never in all my years had to do that. Using silicone to stick in a piece of something to cure rotten cast iron doesn't sound right to me. With respect of course.

 

[Madrab]

I've improvised many times with cast that's been hacked apart with a hammer or roughly cut tight to a wall, avoiding having to dig out sections through the wall. Especially when it's in a bathroom 40ft up in a 1900's tenement. Many times where an old lead sleeve has had to be cut out due to the cast being corroded and it's leaking through the putty. I find the 4" cast knuckle is so thick that it can be ground back and then sealed up. Don't get me wrong it's not silicone sealant - it's a waterproof polymer adhesive I use - it's sets to a solid hard rubber. I even use it to set 50mm plastic waste into a 2.5" cast waste wastepipe to avoid having to remove large section of old cast that, in general, is in good condition.

Too many times I've had calls back to cast that has leaked again after using finned adapters straight into the old cast, so I now take it a step further and make this type of repair and luckily its so far so good.

 

[tonton]

I usually trim down a piece of the soft extension pipe to fit. Trying to remember which of the 4" extensions, might be the macfit, that has fins that can be removed from the end and that inner piece can be used too.

Do you use these things because the type of plastic is softer than if you used an offcut of 90mm pipe?

 

[Madrab]

Do you use these things because the type of plastic is softer than if you used an offcut of 90mm pipe?

Yes - it allows it to be trimmed lengthways and then a small length to be cut off so it can, in effect, be made a smaller diameter.