Chimney rebuild done last year: cement mortar issue?

[nwrmartin]

Hi,

I live in an old house, mid 19th Century. Last summer, as part of roofing work, I had the two chimneys rebuilt (one was leaning, and in the other the pointing had failed so badly that a rebuild was advised). One chimney is in use with a wood-burning stove, and we had it lined. The other chimney, which has 3 flues, is not in use at all.

The builder said he would use a 4:1 sand/cement mix. I suggested a 3:1 mix to deal with weathering, and he agreed.

I have recently been told that given the age of the building he should have used a lime based mortar mix, with no cement. Is that right?

I can see that this matters with repointing; is the issue better or worse given it was a rebuild?

Chimney

• nwrmartin
• 7 Jun 2017

I've also been told his work on the flaunching on the 3-flue chimney leaves a lot to be desired. Here's some photos.

Flaunching 2

• nwrmartin
• 7 Jun 2017

Flaunching 3

• nwrmartin
• 7 Jun 2017

I am not sure whether any of this is a cause for concern (and I'm more concerned about the mortar mix than the flaunching) and if so, what I should do to remedy the problems.

I'd be grateful for some advice. Many thanks.

 

[datarebal]

Your chimney is now built using sand and cement.. Strong mix! What do you want to remedy? The untidy flauncing?

 

[nwrmartin]

Thanks for your reply.

The untidy flaunching bothers me only if it could undermine the watertightness or could cause any other problem. Another roofer (a member of my family, not looking for work) said it could be an issue

On the other point, I'm worried that mortar mix will cause problems in future (cracks in bricks, spalling), as it is not water permeable and is possibly harder than the (quite old) bricks. I've seen this discussed elsewhere in regards to repointing of old chimneys (some people strongly caution against cement mortar) and wondered if it was an issue with a rebuild.

There haven't been any problems, at least not yet, and they've been through one relatively mild winter, but it would be good to know if I should take some kind of action now, whilst the guarantees are still valid.

 

[^woody^]

I have recently been told that given the age of the building he should have used a lime based mortar mix, with no cement. Is that right?

No.

If it is was part of a lime mortar wall then maybe. But the stack is distinct and has no relation to any other wall. Stacks can be built with cement mortar.

 

[datarebal]

i think you instructed the 3-1 mix.. that is strong for the brickwork.
looking again , it looks like you have had some work done to the head of the chimney but doesn't look rebuilt?
one pot looks like its in trouble.

 

[nwrmartin]

i think you instructed the 3-1 mix.. that is strong for the brickwork.
looking again , it looks like you have had some work done to the head of the chimney but doesn't look rebuilt?
one pot looks like its in trouble.

The whole chimney was taken down and rebuilt, for sure. Admittedly I wasn't around when it was done but I can tell, having seen how it was before.

The pot on the right of the photo isn't doing brilliantly, you are right; it probably should have been replaced as part of the rebuild, and I regret not saying something at the time. but I've gotten up close and it is not as bad as it looks, it has some old sealant on it and seems sound for now.

 

[datarebal]

Ok yes I can see on my big screen the pot has sealant on it. Phone screen made it look cracked.

Well going back to the mortar mix etc, The roof has been re tiled using concrete interlocking tiles possibly Redland 50s. The original roof would not have been those.
So, where the original stack was likely to have been built lime mortar it is now built in S & C.
the flaunching is untidy. If its not causing an issue then what is there to claim for under the guarantee? But it might be good just to check thats not a hole next to the pot.
Lime mortar has plenty of good points and the nature of a lot of our work requires/specifies it to be used, Not all trades are truly familiar with it...

 

[nwrmartin]

Ok yes I can see on my big screen the pot has sealant on it. Phone screen made it look cracked.

Well going back to the mortar mix etc, The roof has been re tiled using concrete interlocking tiles possibly Redland 50s. The original roof would not have been those.
So, where the original stack was likely to have been built lime mortar it is now built in S & C.
the flaunching is untidy. If its not causing an issue then what is there to claim for under the guarantee? But it might be good just to check thats not a hole next to the pot.
Lime mortar has plenty of good points and the nature of a lot of our work requires/specifies it to be used, Not all trades are truly familiar with it...

Ok, thanks. Sounds like you are saying the flaunching isn't an issue-it's just untidy and that's it. And that it's not a major issue that a cement mix was used (which Woody agrees with), even if lime would have been better. And as a result it probably isn't worth talking to the bricklayer again. Do I have that right? Thanks.

 

[chappers]

It all looks fine, the flaunching is a bit untidy and the pots could probably have been set a bit better, but otherwise it looks weathertight.

 

[nwrmartin]

It all looks fine, the flaunching is a bit untidy and the pots could probably have been set a bit better, but otherwise it looks weathertight.

Thanks!

 

[Barrule]

Only just come across this thread, so apologies for the lateness
I might be concerned about the concrete roof tiles if the original was slate...there may be quite a weight issue on your rafters

 

[nwrmartin]

Thanks for this. I appreciate the advice. Thankfully, we were advised of this at the time and we had the purlins reinforced as part of the work, so that shouldn’t be an issue.

 

[Jon La]

Looks a poor job to me. The top course of bricks should house the pots. Here, they've clearly sat the pots on the top course of bricks and housed them with the flaunching. If they'd done work to that standard for me, they would not get paid. Needs re-doing.

 

[Jon La]

A 3:1 mix is only suitable for engineering bricks. The mortar will be stronger than the bricks. The bricks will be porous and accept moisture. The mortar will not. Therefore the bricks will fail before the mortar.

 

[datarebal]

Therefore the bricks will fail before the mortar.

one advantage of a lime mortar. mortar needs attention before bricks