Missing chimney crown and a leak - advice sought

[Spoilt Victorian Child]

My neighbour had a loft conversion done (I think) around 7 or 8 years ago. They didn't alter the roof shape, just made the loft into a bedroom, with sloping ceilings and velux windows on the rear aspect.

They have said they have an ongoing leak in the bedroom, beneath where the chimney stack is, which we share.

A chimney maintenance company has said the leak is due to a missing chimney crown head, which was an alteration that was done some years before either of us owned the properties. They also pointed out the poor state of the existing mortar (you can see it's not great from ground level). They have quoted to either remove the chimey stack altogether (all of the fireplaces are currently bricked up), or rebuild the crown head and rake/repoint the existing mortar.

I'd like to understand a bit more about how Victorian chimneys were designed to work with rainwater. Does the crown have a drip sill under it like on a window sill, to stop water running directly down the stack? Isn't that what the lead flashing is supposed to cope with (eg if there's wind driven rain)? Is it possible that just the lead flashing has failed and the roof company are adding on unnecessary work in re-building the crown? Aesthetics aside, is the crown really that important?

Here's a picture of the problematic altered stack (left), and my neighbour on the other side's stack (right) which I presume to be original and with its crown. You can see my stack's been taken down about 6 courses.

 

[Feltwell]

I have my own Victorian chimney woes, as reported elsewhere.

I've not seen a crown with a drip groove like a window cill, but it would help throw some water off. But rain rarely comes down completely vertically, so the side of the stack will get wet anyway.

When you say "leak", do you mean running water when it rains or just signs of damp coming in? If the latter my suspicion would rest with how that chimney has been capped off on top - is it letting water into the old flues, and is it letting water soak directly into the top of the brickwork? That, combined with dodgy pointing, would be easily enough to cause damp. Also, it's hard to see, but are the bricks on the top of the crown on the original chimney blue engineering bricks? If so they are as hard as nails and much more resistant to water soaking into them than the red commons used lower down.

That chimney would look 10 times better if the crown was rebuilt though - and if you've got scaffolding to get up there, it's not a big job, especially if repointing the rest of it. Taking chimneys out is a shame, they really are part of the external character of an old house, and I don't think the cost will be that radically different to getting the current one repointed and the crown rebuilt.

 

[Spoilt Victorian Child]

Ah, just had a look at all the other chimney stacks in the row and their crowns are red bricks, so those blue engineering bricks must've been a replacement themselves. The actual shape and form they take is the same though.

I know the chimney would look better rebuilt, but at the moment if re-pointing is all that's needed and could be done with a ladder, I would hope that would make the cost of the job significantly smaller than the quote I've got (which includes scaffolding) as there's other things that money could go towards.

BTW, the builder suggested using cement for repointing and flaunching – 3 parts cement to 1 part sand. Would lime be better? Would it make much difference?

Also, one advantage of retaining the stack and not taking it down completely is that it leaves the option of re-opening a fireflace for a wood burner or gas fire in the future. With that in mind is there anything I need to bear in mind re the re-flaunching, or is that aspect something better left for if/when that ever happens? At the moment I'm not sure how the flues are capped, but there are no pots or cowls up there that I can see from ground level.

 

[TheRoost]

I'm not sure if they would be prepared to repoint the whole thing just using ladders - we have a similar stack to yours and every roofer that quoted for a repoint & flaunching said that a scaffold platform at eaves level would be required. The scaffold was £250 I think.

Repointing with cement could cause damp problems and the bricks may spall, yes lime would be better - and maybe a pointing specialist that likes lime would be better than using a builder.

I'm not sure what is best for flaunching though - my roofer uses a different mortar for flaunching that is quite light/white in colour, I forgot to ask what he uses, but I assume its not lime based (he's a cement man unless requested) and is probably not breathable.
Maybe someone else can suggest what is best for flaunching on a period property - should it be breathable lime, or with it being very exposed to rain with bricks underneath it, should it be somewhat 'waterproof' ?

 

[Feltwell]

My neighbours got the window cleaner to repoint a stack from ladders, and they weren't even proper roofing ladders. Now he's a nice chap - and he makes a good job of cleaning my windows - but he's no bricklayer, and frankly watching him go sideways across a steep roof 3 stories up with no safety kit was terrifying. His choice I know, but if I'd employed him and he'd fallen off I'd never have forgiven myself.

To do a proper job of repointing you need to rake out thoroughly to a proper depth, and that is not a job I'd want to do from a ladder on a central stack.

Flaunching, I personally would do this in cement -it's so exposed and there's no need for breathability. The rest of the pointing I'm inclined to use one of the stronger lime mixes on my chimney stack, I have spalled bricks that I believe are as a result of the current cement pointing. Be prepared for builder resistance though, most only want to use cement.

If you do get the top rebuilt, which really if scaffolding is going up is not a big job over just repointing what is there, I'd go with blue engineering bricks to match your other stack.

If you're going to use a flue in future for either a gas fire or a woodburner then it will need lining. You could do that at the same time - much easier if you've got a scaffold there - but you'd need to make your mind up now on what you want and of course it's extra expense now. Otherwise, I wouldn't worry - you could put a chimney pot and a pepperpot cap on for now, rather than blanking the top of the flue off with a paving slab, then in the future the pepperpot is removed and a liner and new cap fitted. Speak to your builder though, he'll give you the best option if you intend to bring the flue back into use in the future.

 

[CliffordPope]

I had a lot of work done, including chimney stacks, a few years ago by a small concern that specialised in traditional stonework.
They were generally very keen on using lime, but emphatically said that flaunching should always be cement. The argument was that unlike other situations, you don't want it to breathe or be flexible, you want it to be a solid impermeable cap.
Also of course it traditionally sits on slates.

 

[88v8]

BTW, the builder suggested using cement for repointing and flaunching – 3 parts cement to 1 part sand.

I think that would be three sand to one cement.

Lime is better, but too late for lime now before the frosts.
NHL5 and sharp sand, 1:4.
You mean to do it from a cat ladder? I've worked on a stack from a cat ladder, possible but hard on the knees. I'd not want to do a whole repoint that way.

The flaunching could be done in cement, although I think I used NHL5 when flaunching our pot a couple of years ago, I really should start keeping detailed records.
One reason builders don't like lime for flaunching is that it's not a one-shot job; over several days one has to get up there and damp it and whack it with the churn brush to consolidate and take out drying cracks. OK for a DIYer, not so good for a busy builder unless he's on site anyway.

Leaks... your neighbour's nice clay tiles have been taken off and replaced with ugly modern ones. Insofar as one can see from the pic which isn't very far, the leadwork looks a bit hmmm. I would look to their leadwork for the source of the leak.
Someone on your street will have a drone they could send up to take better pics.

Ivor

 

[steveb]

Our new chimney stack was flaunched with lime as that's what the builder just did and I didn't question it.

It was as Ivor says a multi-day, multi application affair. First layer was described as "lime concrete" so a lime, sharp sand and bits of crumbled up breezeblock in as aggregate, then at least one more layer of finer and finer mortar.

The old cement flaunching that was originally there had mostly detached itself from the top layer of the bricks and had cracked 3 of the pots where it attached to them, presumably due to thermal stress during expansion. The theory is that lime is more forgiving but only time will tell

Quote from builder when taking it down:
"Very hard cement !! As is Devon way .. we may have to source some 2nd hand red imperial bricks for re build . Had they not been repointed in lime they would have lifted n cleaned but cleaning flaunching n pointing that is harder than face of brick is resulting in bricks braking or spoiling of face ... New n 2nd hand imperial are commonly available from Midlands up but north Devon tends to say there's no demand .. but I will ask .."




This was after one or two coats of lime , there was at least one more to go

 

[88v8]

Crumbs! Never seen pots cracked through like that.
The original flaunching looks to have been very thin.

Our local Travis Perkins usually has a pallet of imperial bricks. Saves a trip to the salvage yard.
And of course the salvage yards only have bricks because they were originally laid in lime.

Local chap doing a barn conversion was surprised when I criticised him for laying reclaim bricks in cement. Apparently allowed by the CO. Huh.

Ivor