Taking down chimney, restoring or replacing it?

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jsmac
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Fri 20th Mar, 2020 2:12 pm

oops, posted in error...
Last edited by jsmac on Sat 21st Mar, 2020 11:52 am, edited 1 time in total.

malcolm
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Re: Taking down chimney, restoring or replacing it?

Post by malcolm » Fri 20th Mar, 2020 7:51 pm

Nice work there @jsmac. It's fun doing chimneys. Mine were easy without the concrete render http://www.the-salutation.co.uk/blog/chimneys/ Yours have been more neglected and more concrete rendered so a bigger job. Good to see you taking on that job, and do keep posting pictures as it will inspire not only chimney newbies but also some of us (me) who need to be reminded to get on with stuff.

Zebra
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Re: Taking down chimney, restoring or replacing it?

Post by Zebra » Sat 21st Mar, 2020 9:32 am

jsmac wrote:
Fri 20th Mar, 2020 2:12 pm
Apologies. I made this post as a reply in error. I'm not sure how to delete it...?
Don't think you can delete a post altogether but you can go back and edit it and replace all the text with "oops, posted in error" or something like that.

jsmac
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Sat 21st Mar, 2020 11:51 am

Thanks, Zebra. Good call :)

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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Mon 27th Apr, 2020 10:25 am

Hi everyone,

In our ongoing battle with the most oversized chimney in Kent we have removed another four courses of bricks in an attempt to get to a layer of bricks that isn't wrapped in roots and is relatively structurally sound. I say relatively because its integrity is definitely getting better but the internal bricks are a bit of a mess. It seems that they didn't use whole bricks internally for the most part. There is a mix of half, quarter and little bits of bricks held together with mortar. There is a mix of different mixes of mortar so I suspect that the top of the chimney has been rebuilt at least one other time.

We used an angle grinder to score the render as this was the only way to get it to break where we needed it to and to not disturb the brickwork lower down. It was actually pretty successful (unfortunately I didn't take a photo :? ) and we now have the chimney level and looking much better than it did when I took the attached photo. So now I'm wondering what the best way is to rebuild the chimney.

As I think I mentioned in an earlier post it is unfortunately not possible to remove the cement render without the bringing the entire chimney down with it. So I have reluctantly accepted that it is likely going to have to stay since it is at least partly helping to hold the chimney together. There are a number of cracks in the render which will have to be repaired so I am hoping to get some advice as to best go about this. Is there a type of render that can go over the existing render? Is it best to simply repair the cracks? How best to go about this?

Assuming that we can get the rendered section of the chimney watertight and looking a great deal more aesthetically pleasing than the worn brown cement render we're currently looking at we will then build the top back up. Again I would welcome advice on how best to do this. We plan to install a wood burner in one of the fireplaces so will install the flue for this and cap the other five chimney pots.

I should add that we likely won't do the actual brickwork - I just want to gather as much information as I can before speaking with bricklayers. We have enough reclaimed bricks from another project so we could use them and just leave them exposed rather than rendering the top of the chimney. Is it a good idea to include lead flashing and damp proof course between the newly rebuild upper section and older rendered lower section? Is there another way to do this that we haven't considered?

As always thank you in advance for your thoughts and advice.
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malcolm
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Re: Taking down chimney, restoring or replacing it?

Post by malcolm » Mon 27th Apr, 2020 7:13 pm

It probably is worth putting a bit of flashing on top of the old render edge so that water doesn't get behind the concrete render and push it off. If the render edge looks a bit odd being straight cut all the way around then cut it a constant level above the roof line and use stepped flashing on the falls to hide the sins.

If it were me I would rebuild the chimney with 3.5 lime mortar and bed the pots in a beautuful cement flaunching which goes slightly past the edge of the decorative chimney top.

Don't use any sort of damp course - the bricks laid in lime will be happy evaporating water away and will help the courses of bricks underneath stay dry too. Wet is a bad thing for lime as the soft upper courses demonstrate. Cement render and a badly maintained capping did that.

Not sure about crack filling in cement. Cement will crack again. Maybe something flexible. PU sealer springs to mind. It's a bodge but cenent was a bodge in the first place.

Zebra
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Re: Taking down chimney, restoring or replacing it?

Post by Zebra » Tue 28th Apr, 2020 7:33 pm

What height above the roof are you in this latest picture, jsmac?
Flashing around the top of the render will be necessary, to hide the top edge of the render.
As for damp proof course, my memory fails me but I do seem to recall it being recommended by someone (was it our expert leadworker DJH?) in another thread discussing a similar situation. Would have been a while ago though.
I agree that it's fine to have it without. Here I have a chimney (all but) rebuilt in NHL3.5 with no DPC. But if you had the opportunity to do one, where would it go, at the level you're at now, to prevent moisture getting from the top part, which you're rebuilding, down into the lower part? In which case I can't see the harm. Presumably the mortar below where you are now is lime, but with that render, you'd want to prevent moisture getting in, as it can't evaporate.

Feltwell
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Re: Taking down chimney, restoring or replacing it?

Post by Feltwell » Wed 29th Apr, 2020 8:47 am

My view, and it is only that, is that a DPC would only really do much if low down in the stack - but - I'd then be concerned about it weakening a tall stack. Wind pressure wants to push it over, introducing a weak spot near the base would seem to be a very bad idea in a tall slender stack. In a short fat stack, no problem.

It was discussed a bit in this thread:-

viewtopic.php?f=1&t=16671&hilit=chimney

Putting a DPC up high in the stack? Can't do much harm I suppose, not sure it will do much good either mind.

Cracks in cement render - if you don't want to remove what is there then you must at least go round it all with a hammer and make sure that what is there is well attached, anything that sounds hollow has to come off. If that does just leave you with cracks then I'd rake them out to be an inverted V - i.e. wider against the brick than at the surface - before filling. A sealant would give some flex - CT1 isn't cheap but sticks like the proverbial to a blanket and can be overpainted - if you go for that buy an aerosol of their "Multisolve" as well, you'll need it to smooth the sealant off. There are cheaper options but CT1 is very well regarded, I've used it as a lead sealant (lead to brickwork) on the chimneys on the above link, as I don't want to have to be up there again for many years!

One thing I would consider is when you do the flaunching. This is one - perhaps the only - area where I consider a cement mortar to be necessary, you want something that really will withstand the weather and not crack or pull away. I'd advise mixing some cement fibres in with it - Toolstation sell "fibres for concrete" - and using SBR bonding agent, again Toolstation sell it (& are open for click & collect orders currently). You mix the SBR up with cement powder and paint it on as a primer before you apply the flaunching, and you also add SBR as an admixture into the flaunching mix - it acts as a waterproofer and bonding agent. The fibres act like hair in lime plaster, provide reinforcement against thermal cracking from expansion.

jsmac
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Wed 15th Jul, 2020 12:30 pm

Thank you all for your replies and apologies for my late response.

It's been a couple of months and so I thought it time for an update on our ongoing chimney saga. In the end we decided that it was best to take it down and rebuild it. All in we shifted about 5 tons of bricks, mortar and render but thought of it as a lockdown bootcamp. It was very good exercise and we've ended up with several hundred yellow stocks that will be used in a garden wall.

Unfortunately the cracks in the cement render were too many and too big to be confident of an effective repair and we certainly did not want to have to get up there again in a year's time to make further repairs. We also needed to get a look at the gully between the two pitched roofs that runs under the chimney (imagine a 2 metre lead tunnel about the width and height of a brick) because we were certain that that was where the much of the water ingress was coming from. Having now revealed the gully for the first time in 150 years it is extraordinary that it was build like this in the first place and no wonder the house has suffered so badly as a result. The lead is not lapped into the mortar and since the gully is only about 2 inches high it would have regularly overflowed during heavy rainfall. It was also full of 150 years of buildup since sweeping a gully under a chimney was impossible. So we're confident that we've made the right choice in taking down the chimney since we can now rebuild something in its place that will actually keep the weather out.

Now onto that 'something'... This is where we've gotten stuck and I'd welcome any advice and recommendations on this. We would ideally like to be able to use two of the six flues but the only thing that all of the bricklayers agree on is that it would be best to rebuild it to the same footprint as it was originally since this would be the most stable. Every other recommendation from each of the bricklayers is in contradiction with each other. Use NHL 5, definitely don't use lime, use blocks and render, use stocks, etc. If everyone came up with more or less the same solution then we could take a decision based on price, perceived competence and availability but unfortunately that is not what we're dealing with. When you include the wildly different costs each bricklayer has come up with (£9000 or about £9 per brick?!) it's dizzying just trying to make sense of it all.

Do any of you have any experience with using lime in an exposed location very close to the sea? We've been advised that it may not be a good idea to rebuild with lime since the deterioration of the lime in the sea air might have lead to the failure of the chimney which is why it was rendered in the first place.

Other advice is to use NHL 3.5 and yet more was to use NHL 5. We have someone coming for a look tomorrow that has used blocks and render with good results in London so that is another option apparently but I've read that it is not then possible to use the flue.

Clearly we have to choose one of the options but as this is going to be expensive we want to be confident we're making the right choice. Any advice of materials and expected cost for a stack about 1000-1200 bricks in size would be most welcome.

Many thanks.
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Flyfisher
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Re: Taking down chimney, restoring or replacing it?

Post by Flyfisher » Wed 15th Jul, 2020 1:29 pm

Sounds like you were right to bight the bullet and rebuild the whole thing properly, especially if you can improve the gulley and prevent future overflowing problems - that alone will probably make it all worthwhile.

I’m not sure why a chimney liner should not be installed if lime mortar is used to rebuild the stack. I’ve never seen or heard of any such advice and we’ve had four liners Installed in four different stacks that would have been originally built with lime mortar. No problems yet, though perhaps 10 years is too soon to know for sure.

As for lime and marine environments, I have no personal experience but this information suggests it is fine, even better than cement actually!
http://www.stastier.co.uk/articles/pres ... ritage.htm (Some way down the page).
If it performs well in harbours and lighthouses then I’d guess it was probably ok. Perhaps contact some other lime producers/suppliers and see what they say?

Zebra
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Re: Taking down chimney, restoring or replacing it?

Post by Zebra » Wed 15th Jul, 2020 4:41 pm

Not as big a chimney as yours, and not a marine environment, but I used NHL3.5 to (all but) rebuild a chimney about 9 years ago, and it's been absolutely solid. I used 3.5 because of the softer old red bricks, but you NHL5 would be a good idea if your bricks were harder, the rule of thumb obvs being that the mortar should be softer than the brick. Not very helpful, but thought I'd chip in.... Which would be better aesthetically in your opinion, brick or rendered block? I would tend to think brick, no? Then you haven't got the risk of the render cracking in the heat from the fire.....

steveb
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Re: Taking down chimney, restoring or replacing it?

Post by steveb » Wed 15th Jul, 2020 4:56 pm

we had a chimney stack rebuilt in a marine environment in lime. A bit early to declare long term success but the previous chimney was built of bricks bedded in lime and sand from the beach - so hardly a quality controlled environment - and lasted 120 years.

jsmac
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Fri 17th Jul, 2020 11:26 am

Thank you all for your input. We're going to with brick because as Zebra has suggested render will crack eventually and bricks will be more in keeping with style of our property and those locally.

I agree that NHL (3.5 or 5) would be best to use but unfortunately finding anyone locally who is willing to work with it is nigh on impossible. And when we do find someone who is familiar with working with lime the cost is prohibitive.

Does anyone have an idea of how long it should take to build an approximately 35 - 40 course high stack with natural hydraulic lime (each course is about 30 bricks)? I realise that this is a 'how long is a piece of string' type question but I just don't see how labour-only quotes from £5000 to £9000 are achieved. If they're fair and in line with others' experience then please do let me know.

The person who we spoke with yesterday was competent and could at least appreciate how to join up the plan to rebuild the gully with the chimney (most of the people who have had a look are either bricklayers OR roofers and so we would need to coordinate between them which is something we are hoping to avoid). However, their bricklayers don't work with lime and so want to rebuild the stack with reclaimed or new yellow stocks and a mix of soft sand, cement and plasticisers. Sigh...

a twig
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Re: Taking down chimney, restoring or replacing it?

Post by a twig » Fri 17th Jul, 2020 9:05 pm

jsmac wrote:
Fri 17th Jul, 2020 11:26 am
Does anyone have an idea of how long it should take to build an approximately 35 - 40 course high stack with natural hydraulic lime (each course is about 30 bricks)? I realise that this is a 'how long is a piece of string' type question but I just don't see how labour-only quotes from £5000 to £9000 are achieved. If they're fair and in line with others' experience then please do let me know.
Doesn't sound too unreasonable to me, two people on a day rate of £250, so £500 a day.

Couple days prep and tidy what's there, 3 days construction, 3 days pointing, day to clear up and a day in reserve.

Bogart
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Re: Taking down chimney, restoring or replacing it?

Post by Bogart » Sat 18th Jul, 2020 12:01 pm

Your flaunching is pretty naff to say the least, classic out of sight out of mind arrangement. Understandable in a way as people never think of the chimney until it all goes wrong. I have to agree with others here keep the chimney as would be a shame to do away with it. Plus now you have scaffolding ideal time to drop a liner down for the log burner. And get a price for the job not day rate stuff. And brown envelopes are always a good idea :roll:

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