Lime pointing failed

[KelvinM]

Hi there. I had some quite extensive work done on my house 4-5 years ago. Part of this involved re-building some brick plinths using lime mortar after taking up a concrete floor and replacing with a suspended wood floor. Concrete had been causing damp issues. Now the mortar joints are failing - basically below a certain level the lime mortar is like sand (if I wanted to, I could tooth it all out with my finger a pull out the bricks). This work was done by a local line specialist.

I'm looking for advice on what may have gone wrong. It was a very hot summer when the work was done, and the builder never kept the work damp. I suspect that plus a poor mix led to poor carbonation and now the mortar is breaking down.

My second question is what should I do to remedy this and what lime should be used?

I've attached some photos of the inside and outside of one of the effected walls. Most (but not all) of the impacted areas are below the slate DPC visible in the photos, and it is far worse on the inside of the house.

Any advice would be really appreciated.

Thank you

 

[stuart45]

Do you know what type of lime was used? A hot day with dry, highly absorbant bricks, and then exposed to the sun and not kept damp is a likely cause. You might get away with a repoint.
Years ago, and even today in some of the hotter parts of the USA certain bricks were soaked in water and then allowed to become surface dry. This allowed for a small amount of suction to stop the mortar running down the facework, but stopped too much water being sucked out of the mortar by the centre of the bricks.

 

[Lacan07]

Hi there. I had some quite extensive work done on my house 4-5 years ago. Part of this involved re-building some brick plinths using lime mortar after taking up a concrete floor and replacing with a suspended wood floor. Concrete had been causing damp issues. Now the mortar joints are failing - basically below a certain level the lime mortar is like sand (if I wanted to, I could tooth it all out with my finger a pull out the bricks). This work was done by a local line specialist.

I'm looking for advice on what may have gone wrong. It was a very hot summer when the work was done, and the builder never kept the work damp. I suspect that plus a poor mix led to poor carbonation and now the mortar is breaking down.

My second question is what should I do to remedy this and what lime should be used?

I've attached some photos of the inside and outside of one of the effected walls. Most (but not all) of the impacted areas are below the slate DPC visible in the photos, and it is far worse on the inside of the house.

Any advice would be really appreciated.

Thank youView attachment 11478View attachment 11480

Did they use a lime putty based mortar? This needs careful handling and takes months to fully cure. If you wanted to repoint how about an NHL based mortar? Breathable but stronger and less fussy with a quicker set, you could go for a 2 or 3.5. I use NHL mortar from the Lime centre in Winchester for various jobs and it never fails, you can buy it in powdered form, just add water and keep it as a dry a mix as possible.

 

[malcolm]

Is that leadwork at the top of the plinth? Pull the bottom edge away from the brickwork so it forms a drip edge. Rather than turning back towards the bricks make the edge of the lead vertical so it drops water onto the ground rather than onto the bricks below. That should get rid of the problem of poorly done lime mortar.

 

[Black Timber]

Is it normal for lime to fail after 4-5 years? I thought if it were to fail due to poor application or poor post-treatment/protection, then it would fail sooner than that? I should say I am asking more than suggesting though, and basing it more on what I've read than what I've done! Curious to hear what others think...

OP - are you thinking to go back to the installer to see what they have to say about it?

 

[Black Timber]

Would be interesting to hear back from the OP regarding some of the above responses to their post.

In the meantime, slightly off topic but relevant to the NHL vs hotlime and lime putty is this article:

What Is The Problem With Hydraulic Lime Mortars

There is much discussion in the heritage industry regarding hydraulic lime (N.H.L) mortars and if they still have a place in conservation

www.theyorkshirelime.company

You can find the study they reference online.

I'm hoping it doesn't give the full picture seeing as I've already done a fair bit of work with NHL!

Any thoughts?

 

[Stevers]

From my own experience using tons of the stuff from different sources on my limestone walls over the last thirteen years, the paragraph headed 'Caring for NHL Mortars' just doesn't ring true, in fact I was tempted to be quite a lot ruder than that!

 

[Lacan07]

From my own experience using tons of the stuff from different sources on my limestone walls over the last thirteen years, the paragraph headed 'Caring for NHL Mortars' just doesn't ring true, in fact I was tempted to be quite a lot ruder than that!

Yes, I wondered about that too, I was under the impression lime putty mortars needed much more care and attention as the season is pretty strict and they take months / years to fully cure.

For me the worry is the hardness issue.

 

[stuart45]

Looking in one of my Grandfather's old trade books, it states that chalk(pure lime) shouldn't be used for brickwork.

 

[worms]

Stuart, that looks like an interesting book.

When they say "chalk lime", I would have thought that they perhaps mean straight powdered limestone, CaCO3, as distinct to either quicklime, CaO, or hydrated lime Ca(OH)2 . While most people nowadays would perhaps only ever come across the various lime products used for building, when that book was written agricultural lime would have been a common commodity, so they perhaps needed to make the point not to use straight chalk lime rather than one that had been through the kiln process.

 

[stuart45]

Lime produced from chalk is almost 100% calcium carbonate, so it makes an almost pure air lime. Lime from Lias is more hydraulic as it contains more impurities. The message from the book seems to me to suggest that a pure air lime when used for brickwork will carbonate on the outside first, which tends to hinder carbon dioxide getting to the deeper sections of the joints. As the book was written for the trade, rather than DIY, I would guess that, or hope, that the apprentices reading it would not be thinking about agricultural lime.

 

[Stevers]

Traditionally quicklime was slaked in a hole in the ground before use; inevitably some soil would 'contaminate' the mix, and it has been suggested that this can add mild hydraulic properties.
Interesting comment about the Lias stone dust, because the Mendip limestone dust that we use in mortars does seem to have a life of its own, and my builder was convinced that it helps with the set. I can vouch that an OPC mortar made with just stone dust rings like a bell when struck. Damp Mendip stone dust, will set solid as it dries, but is relatively easily broken up again.

 

[Black Timber]

It's all very interesting, but equally quite confusing too...

Some people seem to advocate the use of hot lime/putty as it is truer to how things were done in the past. But in the past, the lime wasn't pure like it is today. So pozzolans are often added to a hot lime/putty mix to add a hydraulic element for a faster (and stronger?) set, at the expense of a less breathable mortar. In a way, this would make the mix truer to the lime of old, for the reasons @Stevers gives RE impurities. And by all accounts the use of pozzolans goes back millenia, which - if added to the already more impure lime of old - would have made it, well, I guess, doubly impure!

So with Pozzolan added, and the mix having an introduced hydraulic element, what then sets it apart from NHL? In fact, a tutor on a course last year when asked about the roles of pozzolans in a hot lime/putty mix, said "if you're going to add pozzolan, you might as well just use NHL". And that seemed to make sense...

It seems to me that there's a lime theory dog chasing its tail.

But I've only had limited experience in using the stuff, and far more experience reading about! Mostly from the internet too, which isn't always the best place for research. So I'll gladly admit I might be oversimplifying, misunderstanding, etc. Until now though, the hot lime/putty with pozzolan VS NHL question is something I haven't been able to figure out.

 

[worms]

So with Pozzolan added, and the mix having an introduced hydraulic element, what then sets it apart from NHL? In fact, a tutor on a course last year when asked about the roles of pozzolans in a hot lime/putty mix, said "if you're going to add pozzolan, you might as well just use NHL". And that seemed to make sense...

True up to a point, but if you are using your putty bins for a range of different functions, then having a some pozzolan on-hand to add to the mix for the occasions it is needed makes sense rather than trying to keep a separate supply of NHL to-hand and keeping it dry.