Damp in chimney breast - DPC?

[Feltwell]

On one side of Feltwell Towers, built in 1899, is a rather tall 2-flue chimney - on the right of this picture:-

I've got damp staining on the ceiling of the first floor room that contains this chimney breast, and a picture hung on it went a bit mouldy - so it's definitely damp, although an exposed section inside the eaves of the roof above looks fine, and the wallpaper on the chimney breast shows no signs of damp. One flue is redundant - ventilated top & bottom, "pepperpot" cap at the top - and the other is lined for a gas fire that is fairly rarely used.

The chimney breast is not in great condition but it's not bad - it's been cement pointed but it's mostly intact, and there are a few bricks that are spalling - it wants a bit of attention but I've seen far worse.

On the inside face of the chimney, above the roofline, there's a slight projection from the brickwork - looks like slate - that someone has put a fillet of mortar on - looks like it was meant to throw drips away from the face of the brickwork. Has anyone come across this before, is it likely to be a slate DPC that extends all the way through the chimney? Nothing visible from the other side. Here's a picture, taken from my study roof window, unfortunately I'll need scaffolding to get at it up close:-



As you can see the projecting slate looks like it has a bit snapped off at each end. The flashing to the roof should be good - it's only about 12 years old, and I can get directly to the underside of that section, all looks dry, no sign of leaks.

I've always been a bit suspicious of the 2 sloping side sections of brickwork, if they are likely to let water in. I've thought about screwing some treated battens to them and putting roof tiles on them - overhanging the edges by a couple of inches, with flashing into the brickwork above. This is the rest of the chimney above:-



I don't know what the top of the chimney is like, but the roofers I had when the roof was recovered did check the flaunching and reported all was OK. No reason not to trust them but it was 14 years ago I suppose, it could have failed since.

Any thoughts if that slate is likely to be a DPC all the way through, supposedly isolating the stack below from damp from the exposed section above? In terms of way forward I think all I can do is bite the bullet and get it scaffolded all the way round in the spring, rake out the pointing, repoint in lime, and change the spalled bricks. Unsure of what to do with the sloping sections - aesthetically best left as exposed brick but repointed, but if they are the damp source maybe my roof tile idea is worth doing. An identical house on the other side of my town has roof tiles on them.

I'm regretting leaving it a bit late for this year - feels a bit late now to be doing such exposed lime pointing, frosts could come at any time.

 

[Matt Green]

I've got damp staining on the ceiling of the first floor room that contains this chimney breast, and a picture hung on it went a bit mouldy - so it's definitely damp,

If one flue is redundant and vented and there was mould on the picture, then it is probably a condensation issue. That part of the chimney breast will be very cold which will cause water to fall out of the air and be absorbed by or condense upon nearby surfaces.

 

[Feltwell]

It's possible Matt - especially with the other side of the stack being external, it will be cold. The only thing is the damp staining on the ceiling is quite significant, right across the top of the face of the chimney breast - I think it would take a lot of condensation to do that, and I'd see it, but all looks visibly dry. Good thought though, one that hadn't occurred to me, and I'll bear it in mind.

 

[Gareth Hughes]

It prolly has little or nothing to do with the current problem, but the projecting slate course with the mortar fillet on to looks like it's where the lead flashing should come up to, rather than ending at the same height as the top of the ridge tiles.

 

[Feltwell]

I suspect you're right Gareth, but tonight's investigations add weight to it not being the cause of the current problems.

I can almost hear Matt groan as I type this - tonight, I got my cheap Chinese damp meter out and had a good poke around. These meters are notoriously inaccurate but at least give some comparative readings.

So, firstly, the ceiling in the affected room. The area that looks damp registers around 42% on the meter, whereas poke the probes into a dry looking area of ceiling nearby and it's registering only 1 -2 % - so I'm confident it definitely is currently damp. The chimney breast in the room, which is covered in wallpaper, registers 40-ish% all the way across when high up near the ceiling, but as you move down to above where the old fireplace was the readings are 40-ish% in the middle of the breast but only 18-20% near the edges - which implies it's the area around the flues that is the most damp. The chimney breast is covered in wallpaper, but go elsewhere in the room and the readings on the walls (covered in the same paper) are around 10%, so it does seem to be damp. The room on the ground floor shows no signs of damp at all.

So, next stage was to crawl around in the eaves of our attic roof, so directly underneath the ridge tiles on the middle picture above, and have a good look at the bottom of the roof. Here the chimney breast is bare brick - no sign of any damp anywhere, mortar on the brickwork reads 20-ish %, but it may just have different conductivity to the materials tested above. There is one pipe only that passes through the area, it's a modern plastic waste pipe and there is no sign at all of any leakage, so I can rule plumbing leaks out. The brickwork and timbers underneath that section of roof show no signs of any water ingress at all, so I think the flashing & tiles are all good. Roof timbers register about 18% damp but I'm sceptical on the readings as 1 rafter is "doubled up" with modern softwood - so nailed directly alongside each other - and the modern timber registers 1-2% whereas the Victorian timber registers 18%, and they must be at same level of humidity!

I cut out a couple of sections of floorboard to get directly at the top side of the damp ceiling area, all looks fine, but the ceiling plaster squeezed up between the nibs registers 40-ish %. Luckily, no sign of any deterioration in any of the timbers - they all look just fine.

So, as the damp is definitely coming from above, I can only assume it's most likely penetrating damp from the dodgy pointing and the odd dodgy brick on the stack, not helped by the sound pointing being cement based - or possibly bad flaunching at the very top. I was thinking of getting up there this weekend with my scaffold tower - but I can only get to the outside of the stack, and as there are no signs of any damage being currently caused (and the ceiling staining has been there for a while ) I think I may leave it until spring, when I can get it properly scaffolded all round and do the brickwork repairs and repointing properly.

 

[Cubist]

Hi Feltwell,

In the photos it looks like the lead flashing is not lapped over the roof tiles - I thought that was essential - am I seeing things that are not there?

 

[Feltwell]

No, there's no flashing over the top of the tiles - it's been done with soakers and a step flashing - so individual pieces of lead under each tile that turn up the wall ("soakers"), with a stepped flashing covering piece over the top on the wall, which is the bit you can see. Hard to describe but it ensures water can only flow down to the gutter and it allows for movement in the various materials - this picture illustrates:-

http://js-wordpresstheme2.co.uk/home/lsa-pocket-guide/soakers-and-step-flashings/

All dry as a bone directly underneath, so I'm happy they're doing their job.

 

[stuart45]

It should have soakers under the tiles. Dressing the lead over the tiles only really works on profiled tiles.
Sorry, didn't see above post at time of writing.

 

[88v8]

Oh for the days when houses came with such elaborate chimney stacks.

The sides slopes are vulnerable if the pointing is decayed.

The flue that is lined, the flue itself is closed up. Potential problem. Possible to ventilate with a grille or a couple of inch holes near the top (cover with stainless bee mesh), the bottom ventilation method would depend on the fireplace.

I ventilated the lined flue in our sitting room with holes at the top and a gap at the back of the register plate. That eliminated a major damp issue.

It can take years for damp flues to show symptoms on the surface. The unlined flue in our previous house - gas coal - was or seemed fine from 1986 to about 2010, then it became apparent that it wasn't.

Ivor

 

[MikeG]

There is an open perp showing in the photo, at the left hand end of the projecting bricks. It could be that those bricks actually channel water directly at this opening, and this could be at least a partial explanation for the dampness.

 

[Feltwell]

Thanks everyone for the replies. Ivor, that's a good point - I may even put an air brick in, I've got a nice old one that will blend in.

Mike, you could well be right, the pointing is a bit dodgy in places and I hadn't spotted that perp. Whilst I've got a scaffold tower I can't get to the back of the stack with this - come spring I think I'll have to bite the bullet, get a scaffolder out to give me scaffold all around, cut out & replace the bricks where the faces have gone and repoint the whole thing properly in lime. Not a job I relish, but there we go, do it properly and I should be able to leave it alone for many years.

 

[Tom-H]

As above, the pointing looks like the biggest suspect.

An alternative issue could be something I experienced, I had a largish damp stain on ceiling next to the chimney breasts. Multiple attempts to weatherproof the chimney from outside had no effect and the patch kept getting bigger. I even resorted to sitting in the loft during heavy rain, yet still couldn’t see any water getting in.

Something I did notice above the ceiling was LOTS of soot (the original lathe ceiling), this coupled with a very likely historic leak had turned the plaster hygroscopic. This was above the staircase to the attic so all the moisture in the house ended up here and was being absorbed by the plaster.

 

[DJH]

It seems to me Feltwell that the construction of those shoulders looks to be designed to channel water/damp directly into the main structure of the chimney :shock: . Rainwater penetrating the slope of the brickwork shoulders through the mortar is directed down into the chimney.

I suggest that you consider cladding these sloping areas with lead fixed at the top with a flashing to both cover the fixings and weather the abutment of the lead against the stack. The lead should be wide and long enough extend about three inches over each side and end so that it can be folded over to weather the side brick perp joints. If you welt these edges it will help stiffen it against wind lift. Copper clips incorporated in the welt would be best.

Best to paint the underside of the lead with a hard black bitumen paint the one we used to paint oil storage tanks with.

Doug

 

[88v8]

And then when you've done all that, for an exorbitant sum you can offer to do the same for your neighbour

Ivor

 

[Feltwell]

Thanks everyone for the replies. Not much chance with the neighbour Ivor, they're not very PP minded, I live in fear of looking out one day to see a UPVC fitter's van. But they've been there 13 years so far, so fingers crossed they will keep their wooden windows (although theirs are not original - mine mostly are)

Welcome back Doug! You've been very quiet of late.

What a surprise, you thinking of covering something in lead :lol: But you're right of course, and it was a thought I'd had myself. The only thing that tempted me towards using tiles was the ability of an overhanging tile to throw water away from the bricks immediately underneath, and cost - realistically, to get a properly professional looking job in lead, I'll need a proper professional to do it! Using Quinn again is an option of course, he did a great job for me before, but he's proving very difficult to pin down at the moment - the plumbing side of his business seems to have gone into overdrive, he's got a job at a hospital that seems to be never-ending.

I'm in 2 minds really if just re-pointing the slopes properly will be enough to do the job, because I agree, the design seems ideal to push damp down into the stack.

Why paint the bottom of the lead in bitumen paint by the way? If it's to ensure it can move over the brickwork, would a heavy building paper not do the same job? I seem to remember Quinn doing something like that when he put lead over the terracotta string course on my porch.

 

[MikeG]

.......to get a properly professional looking job in lead, I'll need a proper professional to do it!........

I don't agree with this, unless welding is involved. Leadwork, on a small scale (and not involving welding) is really pretty easy, and most competent DIYers would manage it reasonably well. I've certainly never needed a pro to do any leadwork on my various properties over the years.

 

[Feltwell]

I'm sure you're right Mike, my thinking being unduly influenced by the beautiful job a pro leadworker did for me last time - a job that was a lot more complicated and yes, involved welding. I'm sure I could do this one myself if I put my mind to it.

 

[88v8]

When my lead has failed, it's been due to insufficient laps, and overworking leading to cracking.
I made a complicated back gutter behind the roof hatches of a small conservatory that I built, and for 25 years it leaked. A slow drip drip in heavy rain. Never could find it, but basically not enough rise &/or lap. Fortunately the roof was cedar, so no harm done.

Recently bought a welded lead ridge cap here https://www.justlead.co.uk/product/lead-ridge-abutment-flashing/. Their product line may not be germane to your immediate needs, but worth bookmarking.

Ivor

 

[stuart45]

He used to have a load of videos on leadwork at one time on utube.

 

[Clockmaster]

I have not properly read the other posts, so excuse me if this is being repeated. You mention lime pointing. Were builders using this on new builds in '99? Those canted bricks either side of the stack would be getting a good coat of looking at if this was my property.