Cast iron soil stack through tiled pitched roof -lead flash?

17 Aug 2003
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United Kingdom
Hi All

I recently had a roofer replace the cement join on my roof tiles with some lead flashing and all is well apart from around the hole where my soil stack goes through the roof.

They have used lead sheet flashing around the hole and then cemented on top of it and around the pipe. It has been fine for many months, but I have noticed a leak and there is a crack in the cement, so I imagine that this is the source.

Do I simply patch up and repair the cement or do I use a flexible mastic or shall I take the cement off and use an adhesive lead flashing?

Ideas would be much appreciated. I am not sure what the proper way of doing this would be!

Thanks in advance!
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Should be a proper lead boss that slips over the pipe and covers the tiles.

You can buy these from plumbers merchants.

Cement should not have been used :eek:
dont think they could have done that - the pipe has been in situ for over 70 years and they would not have been able to get the boss over the pipe. Looking at all of the other properties around me, they all have a cement flashing.

Given that the pipe cannot be moved, is there anything else I could try?
sounds like they applied a coat of kidology :rolleyes: Were they itinerants on their way to Essex :LOL: try some mastic in a tube ,as you thought
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yes! Well they are from Essex and they were very rough!! ;)

Any particular type pf mastic in particular? I have some HMA Multipurpose clear silicone - do you think that would adhere to the cement and the pipe?
Nothing wrong with Essex roofers, it's who you know that counts.

Corrado, would one of these do the job ? Because it has a flexible rubber centre it can often be pulled down around pipe collars etc.
looking@the dow corning booklet and it appears that Geocel All Weather Mate would be one..... or Roofers Mate .same make .........maybe I should`ve said Sussex as their destination :oops: ;)
Thanks for those replies.

The flexislate is a no go as the pipe is flush up against the wall and cannot be moved easily.

It seems that one of the adhesives would be best unless there is a half moon type collar on the market that could be applied if the pipe was the remain in situ.

Otherwise, shall I leave the cement undisturbed and use one of these adhesives to seal the join between the pipe and the cement collar?

Given the way the pipe is, would they have had any other solution?

By the way, the SVP is about 3metres tall running up flush against the outside of the house.
Corrado said:
- the pipe has been in situ for over 70 years and they would not have been able to get the boss over the pipe. Looking at all of the other properties around me, they all have a cement flashing.

that` s the crux of the matter......the cement fillet was a common way back then ..........I would just seal the cracks ;)
The roofer came back again today and re-did the cement. Once it sets, I will put some sealant around the pipe anyway, just in case.

Thanks for the responses. Much appreciated.
Might be an idea to fit a storm collar over it, you can get the right size pipe dia or adjustable type
Amazing, Masona

That looks pretty good. Where can I get those, do you know?
A good plumbing merchants should have them, I know plumbase do them.

Plenty online on goggle

Bought mine from but the Online Shopping Cart is temporary out of action

Loads from

Best to get adjustable type, run a sealant on top, you may get away by sealing the bottom if it can rest on the base! Also get a high temperature sealant if needed for heat.

Looking at roofer link, I believe you can just buy the rubber cone with out the backing plate so maybe you could fit one of them over it and seal the bottom which will be better than cement etc

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