Help with my damp spot, please

[TooLateForAName]

I rebuilt two of our chimney stacks myself earlier this year.

Water was causing damp patches below one of them and when I went up to look I found that the old lime mortar had given up. Water was clearly getting in around the pots and the corbells. Was a bit tricky getting the very heavy old pots down when they were sitting on a pile of loose bricks.

I bet you'll find that the mortar around the cap is loose. If the chimney isnt used why not just remove it?

[Wayne E Edge]

Hard to say if it is the cause, but that chimney has no DPC and will be without doubt letting in somewhere. They are notorious for it. I get hundreds of calls about chimneys.

[Lemming Train]

If you don't spot any cracks or obvious problems when you're up your ladder, stick a piece of polythene over the top of the chimney (if it's not in use, obviously) and secure it round the stack with some string. Monitor situation in bathroom through a number of rainy spells and see if it stops. It's just a process of elimination really. Eventually you'll do something and the problem will stop imo, at which point you can either see about fixing it yourself or getting a trade in to fix the specific problem without needing to pay them to find out what's causing it as well.

[BackPedal]

Once again, thank all for your replies.

So an update:

- I went up there on Saturday to see what was what. There were quite a few gaps and cracks in the pointing and stone work so (maybe wrongly, please advise?) I siliconed up what I classed as a larger gaps. I guess the problem with this is that the holes I've filled could be ingress holes for water rather than egress holes. But, my logic for filling them was to rule out the pointing needing redoing.

- There were also some gaps between the top of the roof and the chimney flashing so I filled those best I could with silicone. Hopefully this'll rule out the roof being at fault or the lead flashing around the base of the chimney.

- I also removed the grey mushroom that was the exhaust for the extractor fan. Turns out that very little air could get out. On the positive side, the extractor has a solid 100mm pipe through the wall so there shouldn't be any damp coming from that. Negatively, it doesn't run down towards the outside. Anyway, I replaced the mushroom with a gravity flap cowl. This'll hopefully go some way to reduce the amount of moisture in the room during shower time.

- I couldn't get my hands on a suitable ladder to look at the top of the chimney but I should have one this week so will go up there and inspect. I'll throw a tarp over it and attach that to the chimney. Hopefully this'll eliminate the chimney being the source of water ingress.

Once I've got to the bottom of that I'll know how to proceed with getting a builder in...

Thanks all!

[Wayne E Edge]

Your chimney flashing might be fine but still won't stop damp passing by without a DPC.

I've been a roofer for 40 years and the amount of times I've heard....."I have water leaking around the chimney, must be a flashing issue" is unbelievable.

Someone said earlier in this thread about lofts used to be lofts and you wouldn't notice. As soon as you make a liveable area there it comes to one's attention. Well, he's bang on. Another thing with old chimneys is they were expected to have heat put through them from the fire. That is why they never bothered with a DPC.

If I don't get a dozen calls this month about this same issue I'd be surprised.

[BackPedal]

Wayne E Edge said:

Your chimney flashing might be fine but still won't stop damp passing by without a DPC.

I've been a roofer for 40 years and the amount of times I've heard....."I have water leaking around the chimney, must be a flashing issue" is unbelievable.

Someone said earlier in this thread about lofts used to be lofts and you wouldn't notice. As soon as you make a liveable area there it comes to one's attention. Well, he's bang on. Another thing with old chimneys is they were expected to have heat put through them from the fire. That is why they never bothered with a DPC.

If I don't get a dozen calls this month about this same issue I'd be surprised.

I see - so where does the DPC go on the chimney? Would putting a tarp over the top of it help temporarily?

Many thanks.

[Lotobear]

The dpc needs to be built into the chimney at the time of construction - it is formed in lead sheet and is introduced to coincide with and lap over the external cover flashing and then also has an upturn within the flue. It's a complete barrier running through the entire structure of the stack masonry

Your only other option is a good render system without taking down the stack and rebuidling with a dpc tray but that's a compromise.

You could take the stack down and roof over but you lose something aesthetically with that approach especially on an old building (IMO)

[BackPedal]

Lotobear said:

The dpc needs to be built into the chimney at the time of construction - it is formed in lead sheet and is introduced to coincide with and lap over the external cover flashing and then also has an upturn within the flue. It's a complete barrier running through the entire structure of the stack masonry

Your only other option is a good render system without taking down the stack and rebuidling with a dpc tray but that's a compromise.

You could take the stack down and roof over but you lose something aesthetically with that approach especially on an old building (IMO)

Ah ha, yes, sorry, I thought there was an additional DPC beyond the lead trey that another member described. I think in this instance (if the chimney is leaking - and it sounds like it almost certainly is) finding a solution that doesn't involve taking the thing down is preferable. I'll get that tarpaulin to start and go from there...

Cheers!

[Lemming Train]

Aluminium foil experiment results?

[BackPedal]

Lemming Train said:

Aluminium foil experiment results?

Ah yes, sorry, I forgot about that. The area covered by the aluminium foil square was wetter that the rest of the wall. Doh.