Taking down chimney, restoring or replacing it?

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

Post by Kearn » Mon 20th Jul, 2020 12:23 am

a twig wrote:
Fri 17th Jul, 2020 9:05 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by Bogart » Mon 20th Jul, 2020 2:50 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by Kearn » Mon 20th Jul, 2020 4:17 pm

Bogart wrote:
Mon 20th Jul, 2020 2:50 pm
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
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Re: Taking down chimney, restoring or replacing it?

Post by malcolm » Mon 20th Jul, 2020 4:31 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Tue 21st Jul, 2020 5:27 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by malcolm » Tue 21st Jul, 2020 6:05 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by jsmac » Sun 16th Aug, 2020 1:59 pm

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

Post by Zebra » Mon 17th Aug, 2020 3:24 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by Zebra » Mon 17th Aug, 2020 3:38 pm

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
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Re: Taking down chimney, restoring or replacing it?

Post by Feltwell » Mon 17th Aug, 2020 5:11 pm

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/l ... ime-mortar

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

Post by jsmac » Thu 20th Aug, 2020 2:19 pm

Thank you Zebra and Feltwell.

I had looked into pre-mixed lime mortars and I think that this is the likely route that we will take. This way at least we can be certain of the mix and the quality of the sands used. I have tried to speak with Lime Green but puzzlingly they wouldn't transfer me to their technical team because I am neither an architect or a company. As baffling an approach to customer service that I have experienced in a long time.

Interestingly, one of Lime Green's merchants told me that their premix mortar contains a mix of sharp and soft sand. He thought that it was a 50:50 mix of sharp and soft sand in a 1:3 ratio of lime to sand (but couldn't be certain and suggested I speak with Lime Green to confirm :| ). They also do their own mortar called Ironstone that uses that same mix with sands local to them so this could be an option.

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

Post by a twig » Fri 21st Aug, 2020 8:00 pm

Just tell them you are an architect, or that you are a sole trader - simples :)

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

Post by Feltwell » Fri 21st Aug, 2020 10:11 pm

PM sent Jsmac.

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

Post by jsmac » Mon 24th Aug, 2020 5:46 pm

Thanks, Feltwell. I've replied to your PM.

Our bricklayer is very reluctant (ie. no chance we'll be able to convince him) to use any kind of premixed mortar :roll:

I'm now looking at getting sand delivered from one of the companies that makes the premixes (Lime Centre and Womersley's have been very helpful). They sell properly graded and washed river sand and grit sand which is my main concern with buying soft sand from one of the main building suppliers.

I hope to soon be able to bring some positive news and photos to this thread :)

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

Post by jsmac » Tue 13th Oct, 2020 2:07 pm

Chimney rebuild victory!

After countless hours spent researching sand, NHL, bricks, chimney pots, etc. we finally completed the chimney rebuild this past weekend. We used a mix of fine and coarse sharp sands and NHL 3.5 in a 2.5:1 mix for the bricks and a NHL 5 : sharp sand mix for the flaunching. The bricklayer suggested using a half bucket of cement in the flaunching mix because of the high winds and the long setting time of NHL. This seemed reasonable so that is what we went with. We still need to get the roofer in to roof over the redundant chimney stacks and do the leadwork but actually getting this chimney rebuilt feels like quite the accomplishment. I'm pleased that we stuck with it despite all the times that it would have simply been easier to roof over the lot and be done with it.

Thank you to everyone for chiming in with suggestions. I'll update the thread when we've finished the all the roofing work and the installation of the twin-wall flue chimney.

Cheers.
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