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Weeds Growing in Join on Soil and Vent Pipe - Will they Cause Damage?

Postby DrQuincy » Fri Jun 12, 2015 1:24 pm


I live in a Victorian terrace. We have a cast iron soil waste pipe and over the last couple of months weeds have started growing in the exterior pipe that joins the waste from the toilet the the main pipe.

It's been too high up for me to do myself until I get hold of some ladders. I'm hoping to get it done next week as they are growing fast.

I'm no expert at all but the pipe seems in decent condition. I can see from other parts of the system lower down that whatever is used to join the parts of the system together has gone brittle and cracked so a few bits of muck have got in and ended up growing weeds. Only some of the exterior has come off; it seems firmly joined.

The pipe itself looks intact. I was just wondering though, what is the likelihood that in a few months these weeds could've caused damage to the pipe? Is there any chance the roots could've made it right through? When I come to clear them, as an absolute novice, what should I look for to see if any damage is done? From what I can see wherever two parts of iron pipe are join there is an iron ring joining them together so it looks unlikely roots could've made it that far through in a relatively short time.

Should cast iron soil vent pipes be re-connected every x number of years? If so, what would it cost?

Thanks — and sorry if I've used any of the wrong terminology!
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Simply Build It

Postby plumbbob » Mon Jun 15, 2015 8:25 pm

There is no need to replace a cast iron stack if it appears to be in sound condition. Just check if it is firmly fixed to the wall, and that all joints are sound and there are no obvious cracks in the pipe itself. I have known the swan neck part which often is fitted at the top to step out past a guttering to fall off if the jointing compound has broken down.

The weeds themselves are unlikely to pose a threat, but it does indicate the sealing compound which is usually a weak cement mix, is breaking down. Apart from the danger of a falling piece of pipe, the joint may start to leak and future cold weather can freeze any water causing the joint to fail rapidly.

Best to get up there and chisel out the seal and replace with a fresh mix.
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