Taking down chimney, restoring or replacing it?

[malcolm]

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]

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]

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:-

https://www.periodproperty.co.uk/forum/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]

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.

 

[Flyfisher]

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/preserving-heritage.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]

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]

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]

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]

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]

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:

 

[Kearn]

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

I don’t remember the numbers, but there is certainly guidance / rule of thumb adhered to, regarding how many courses high you should lay bricks in lime in one go, so the structural integrity isn’t impacted by excessive weight on wet mortar. At least these were the rules that our chap used when we had to partially rebuild our fireplace....

Whether a day rate or total job price is used, it would be wise to ensure it’s factored into time estimates.

 

[Bogart]

Just so happens have a brickie here now, not using lime mortar as is on a new BBQ. He reckons, if he uses lime mortar,which is not very often, maximum 20 courses in one hit.

 

[Kearn]

Just so happens have a brickie here now, not using lime mortar as is on a new BBQ. He reckons, if he uses lime mortar,which is not very often, maximum 20 courses in one hit.

That’s a much larger number than we were working with - from memory more like 4-5... certainly couldn’t have been 20 as our beam sits at 17! May be a personal preference I guess, no other reference points than our chap - although he was close to his 60s and had been restoring period inglenooks his entire life. Regardless, there will obviously be a huge load variance between 5 or 20 courses on wet mortar....

 

[malcolm]

I'm going for 9 courses. You always win the sweepstake by going in the middle and that is my recollection.

It's nonsense though. You'll be using NHL 3.5 for a chimney and by the time you build up enough courses to put any real weight on it'll have gone off plenty well enough to take the weight. At worst it will compress nicely and that's a good thing for lime. The BBQ I'm rebuilding had 6 levels of bricks for the trial fit of the brick pattern without any mortar at all and it didn't fall down.

 

[jsmac]

Thanks everyone.

The brickie who we will likely use said that they would expect to finish about 8 courses in a day depending on the temperatures so that is in line with what you all are suggesting.

He did come back and say that while he would prefer to use lime that he could use a 'soft' cement mix instead (I haven't had a chance to ask him yet what the mix would be) and it would save us a fair bit of money (probably about a third less). Money is indeed tight at the moment with work being so sporadic these past few months so I would be lying if I said we weren't considering it.

He's very much from the old school of bricklaying and has done a lot of conservation work so I believe he wants to do a proper job rather than just get it done faster but this has put us in a bit of a quandary. There are so many different jobs that need doing that saving some money here would be very much welcome in actually getting this house habitable but I know that using an NHL mix is ultimately the better course of action.

Old houses, eh? My next house might just have to be a 1970s bungalow.

 

[malcolm]

Not sure how materials affect the price so much. I'm rebuilding my BBQ in cement to match what is there and it's taking me longer because I'm not used to the stuff.

BBQ is on the ground and someone else can rebuild it again when it fails. Chimney is less accessible and it would be mean to do that in cement. NHL 3.5 is ideal for the brickwork. Concrete is good for the flaunching.

You can treat NHL 3.5 like cement. Ideally you would wait a couple of hours for it to dry a bit before pointing, but up on a chimney you won't notice bad pointing so much so might be able to reduce the time difference in return for a bit more brick staining.

 

[jsmac]

After much thought and many conversations with local bricklayers we've decided to rebuild half of the original chimney. It will still need to be over 4m high but by only rebuilding the section with the four flues we'll only need about 60% of the bricks and mortar. We'll also be able to get rid the gully tunnel that runs under the chimney and replace it with a more sensible gully between the two pitched roofs and step flashing all around the new stack.

Since we still need a chimney for one of the flues that isn't being rebuilt at the back of the house we'll install a twin wall flue and fix it to the rebuilt stack. I've attached a photo of a sketch that we came up with in conversations with a local stove fitter. This seems like a best solution to a tricky rebuild. Eliminating the gulley that runs under the chimney stack seems preferable to reinstating it which always seemed to me like a less than ideal solution.

We're going to supply the NHL 3.5 and sand. The bricklayer has said that he's going to use a mix of soft and sharp sand. I think he said he'll use a 2:1:2 mix of soft sand:sharp sand:NHL 3.5.

What does the PPUK hive mind think about that mix? I thought that it was best to use sharp sand only but having never built even a garden wall (yet) I obviously am reluctant to dictate to him what mix of mortar he should use. I would welcome your thoughts on what mix you think would be best for a chimney stack in an exposed location very close to the sea.

The bricklayer has also suggesting parging the flues. He suggested doing it in sand and cement which strikes me as odd. What do think? Is parging necessary for a chimney stack that will be lined?

Also, is there a consensus on what height chimney pot we should use for a stack of this height? We'll need to buy four since the ones that were used previously have seen better days and are probably best retired to the garden. We have an angle on four matching reclaimed ones that are 550mm tall but I'm wondering if perhaps they won't look a little squat on a 4m high stack. It is entirely possible that I am overthinking this, however. :|

 

[Zebra]

I have used that mix - soft and sharp in equal quantities - to build a garden wall and for some repointing on the church wall. It is easier to use but unconventional, and less strong than all sharp. Which is why I only used it on less critical places. I'm a little dubious for something like a chimney. In my garden wall the mortar keeps falling out, although that may be because it's only three courses high and backfilled with soil. The church wall seems OK but it's less than a year ago. I'd get some more expert advice on that to be honest, I'd be a little concerned.

 

[Zebra]

It might be more expensive but have you considered using a ready mixed mortar? I mean a dry mix of NHL and sand... I all but rebuilt (extensively repointed) my chimney 8/9 years ago, and bought such a product, having then the assurance that it's definitely the right mix. Get the mix wrong, and you've got to do it all over again. It was awfully tricky to use - wouldn't stand up on the trowel - so I can see why a user or professional would be tempted to "fatten it up a bit" with some hydrate or chuck in some soft sand. But I persevered and it's stood the test of time so far. And my chimney is way smaller than yours and in a sheltered location. Perhaps you could get some advice from the Old House Store or Mike Wye or similar.

 

[Feltwell]

The brickie who has been doing the repointing here with me here is very impressed with Lime Green's pre-mixed mortar, what it's like to work with. For repointing it's perfect, but for brick-laying from scratch it would be too expensive for most jobs. But - a chimney isn't going to use a vast volume. Use "strong" mix for a chimney.

https://www.lime-green.co.uk/products/lime-mortar/natural-lime-mortar