Damp wall - what am I looking at?

[Andy Dingley]

Damp patch inboard of an outside chimney, with no obvious cause or broken thing to fix.

Late-Victorian three storey, with an external brick chimney for the old kitchen range.

chimney is capped at the top (paving slab), but unventilated at the bottom. It has a lead gutter into the corner of the roof. Access is a pain, as I don't have ladders to do it and there's also a protruding conservatory beneath. a laddery chap up there a while ago to tidy the other chimney stack, and he reported no obvious cause.

Inside has been damp for some years, to the point of peeling paper and the plaster starting to fail. As there's nothing visible outside, and I plan to insulate inside anyway, I've now started hacking the plaster off inside. I hope to find an obvious damp spot, otherwise to tunnel out onto the roof from the insides (at least with an endoscope). Pulling the plaster showed at least three vintages of plaster on there, so I think it's an old problem with some partial repairs done in the past.

Now I've found this

is staring at the inside wall of the chimney, from the turn of the staircase onto the top floor. There appear to be two holes into the chimney from inside, as if they were flues(?), blocked off by bricks placed into them afterwards. Beneath the lower one, there's also a horizontal length of timber set into the brickwork beneath the plaster. Support for the staircase? It's a bit low to be a plate supporting the floor joists.

Why would my kitchen range chimney have "flue holes" in it two floors above? Was this common? Some temporary construction measure?

Any thoughts on de-dampening would be welcome!

[Phil L]

the capping isn't big enough, you can clearly see cracking/algae at the corner. The capping should overhang the chimney by about 3 - 4 inches all around, which means hoiking a 3X2 flag up there like I had to do last week on a church chimney.

Enjoy

[Dave Liquorice]

of the chimeny and the immediatly adjacent bit of wall. I'm sort of assuming that the expose bit of lath/plaster ceiling is the underside of the bit of roof with the bodged mastic.

The cap doesn't look good it ought to over hang all the way round and have a drip groove as well. 3 or 4" seems a bit excessive to me 1 1/2" with the drip groove 1/2" in from the edge.

Personally the mastic is a bodge and that is where I suspect the water is getting in. It will run down the outside of the stack and into the rendermastic joint and behind the flashing. I think that of flashing needs to be properly redone with the fall so water doesn't pool (if it does) and up under the rendering skirt.

I was going to suggest that you took the stack down to below roof level and patch the roof but I see from other pictures that would probably look really naff.

[Andy Dingley]

Thanks. That wasn't something I'd considered. I'd put a camera up there because I suspected there wasn't anything up there at all.

It's certainly the next step to try and fix though (grim task though I think it will be to fix). Do I have to put a bigger slab up, or can I have the flaunching fixed?

If I do slab it, how about 1/2" cement board? (I have some, and it's lighter)

I think it's a bodge over a perfectly good flashing. It was only added by the chap up there last, because he couldn't see anywhere else to stick it and he wanted to do _something_ after all the faffing it took to get up there.

[Tim Lamb]

In message , Andy Dingley writes

Snip..

My two storey Victorian house has 3 flues to each chimney.

The kitchen range, first floor bedroom and ? I think it might have been a boiler for laundry. Ground floor, ceiling level entry so not the same as yours. Could it have been a retro fit metal flued stove for a bedroom?

That chimney capping looks a bit iffy. There is no overhang to drip rainwater clear of the render and no ventilation to clear internal condensation.

Someone with more knowledge will be along shortly:-)

Oh! I see they have already.

regards

[Andrew Gabriel]

In addition to the other comments, the flue needs ventilating top and bottom, or it will gradually fill with condensation, which will come through to the inside as a damp chimney stack. The vents can both be to the outside, so you don't lose heat from the house up the chimney.

[Phil L]

It needs to be heavy duty, if you put anything flimsy up there, the elements will destroy it in short time or it will end up in next doors backyard once the first gust of wind licks it

He probably knew the capping needed replacing but didn't want to do it, but there's no getting away from it, however horrible a job it is. You may need to hire a roofer and/or a cherry picker, failing that, scaffold.

[Dave Liquorice]

Agreed and take note of the last bit. The 3 x 2 slab on the barn stack was moved by the wind here and it only has a small over hang for the wind to gat hold of. It now has some large screws into the stone/brick work below. The OP's place looks as if it might be a bit exposed to SW'ly gales coming up the Bristol Channel.

Scaffold is cheap, I got the impression from some of the other photos that the ground sloped by the base of the relevant wall so a cherry picker might not have suitable access and it looked quite a way up as well, cherry pickers wobble...

Also to easily point the the new slab onto the stack you need all round access.

[Weatherlawyer]

That's what I was going to post. The idea of the overhang is that it sheds water that might otherwise get in from a vent. You only need an half inch or so. Take a brick off one of the sides in the middle and replace it with two halves of a quarry tile or something.

If you are going to the expense of scaffolding then you may as well take the chimney down below the roof.

The cheapest bodge around the problem would be to drill a couple of holes on the ladder side of the chimney fairly near the top. And maybe stick a couple of plastic tubes in with a slight slope on them the stop rain pouring in.

When you get up there, tie you ladder to the chimney and use a long rope to haul up your drill.

[Andrew Gabriel]

It makes sense to avoid water going in the vent, but it really doesn't matter if it's vented. A completely uncapped flue open to the rain which is vented will stay drier than a capped and unvented flue.

I used a bog-standard eathernware air brick, in place of one of the original bricks. For the lower one, I used a plastic version which allows the grille to be unclipped for clearing out cobwebs, etc. Also found them useful when I was installing central heating, as that proved to be the only way to get long lengths of copper pipe down under the ground floor.

Initially I had no access to the chimney stack above the roof, so I took out half a brick in the loft. Some years later when I had scaffolding up around the chimney, I fitted the air brick properly, just below the corbeling around the top of the stack.

I would not rest a ladder against a chimney stack in unknown condition. When you look down the flues, you will likely see half the mortar has been washed away over the years, and it may be nowhere near as strong as you might imagine.

[Tim Lamb]

The agricultural solution:-)

I just happened to have an almost big enough piece of 3mm galvanised sheet lying about.

I had scaffolding up to re-do the lead work and pointing so access was easy. In the event, the top few courses of brick needed relaying.

The imitation forge canopy is secured by stainless bolts to some galvanised heavy angle fitted inside the flues.

regards

[Tim Lamb]

In message , Tim Lamb writes

Unhappy wrap on my display! Pasted in a browser with the gap between *c* and *h* deleted it worked.

regards

[Allan Plant]

Is there any black mould on the damp areas? If not then the problem is probably acid salts that have leached through from the flue. They will be hygroscopic hence the damp patch. The cause is the kitchen range. Your might stop it with some sort of sealant. One cure is acid resistant plaster. Allan

Andy D> Damp patch inboard of an outside chimney, with no obvious cause or