Green Building Forum - Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? Wed, 10 Jun 2026 11:09:07 +0100 https://www.greenbuildingforum.co.uk/newforum/ Lussumo Vanilla 1.0.3 Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135113#Comment_135113 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135113#Comment_135113 Tue, 14 Feb 2012 10:59:24 +0000 lineweight
So, have been trying to read up on lime mortar and get my head around the options. Unfortunately it seems the more I read the more conflicting advice I see.

That cement mortar is a big no-no I get, and understand the reasons.

As far as I can see, the options for lime mortar are:

1) Lime putty. Non-hydraulic. Mix 1:3 with sand, slow setting.

2) Natural Hydraulic Lime (NHL). Again mix approx. 1:3 with sand. Fast setting. NHL3.5 seems most appropriate to my needs.

3) Cement:Lime:Sand mix using hydrated lime(ie non-hydraulic, bagged lime as available widely from builders merchants). Mix 1:2:9 (or 1:1:6 where more strength desirable). Fairly fast setting on account of inclusion of cement.

I think I'm going to rule out (1) because I'd like something fairly fast setting, especially at the moment with cold weather, and because I've seen comment that it's a bit more difficult to work with and I'm not a bricklayer.

Option (3) is attractive because the hydrated lime is cheap and easy to come by. The potential concern is the inclusion of the dreaded cement, but this kind of mix seems fairly widely recommended for repointing historic brickwork. I am however aware that thinking changes over time and this advice might be outdated.

The reason I'm a bit sceptical about option (2) is that most of the advice saying that I should use this comes from people who are trying to sell NHL. Flexibility and breathability are mentioned as the benefits but is there really a big advantage over say a 1:2:9 mix where the cement content is pretty low?


Any thoughts appreciated!]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135131#Comment_135131 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135131#Comment_135131 Tue, 14 Feb 2012 13:08:22 +0000 jms452
Can you not wait a couple of months (i.e. until its not freezing every night) and go for option (1) it is the mortar that will have been used in the house after all. I've worked with sharp sand (to match existing) and lime putty and wouldn't describe it as hard.

It is also worth some effort to trial the mix first to make sure it does match - the first time I tried repointing it was with some distinctly red sand from BnQ, it looked C*** and I ended up repointing it again!

This may attract some tutting but I've also found that lime putty home-made from non-hydraulic bagged lime is as good as expensively purchased lime putty. Just leave it covered and under water in a couple of builders tubs until the weather warms up.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135134#Comment_135134 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135134#Comment_135134 Tue, 14 Feb 2012 13:14:11 +0000 djh
http://www.buildingconservation.com/articles/pointing/pointing.htm
http://www.buildingconservation.com/articles/plaster/lime-plaster.htm
http://www.spab.org.uk/advice/technical-qas/technical-qa-11-repointing/
http://www.spab.org.uk/advice/technical-qas/technical-qa-21-inappropriate-cement-pointing/
http://www.spab.org.uk/advice/technical-qas/technical-qa-14-lime/

There's also http://www.shetland.gov.uk/planningcontrol/advicenotes/documents/AdviceNote13-LimeMortarsandRenders.pdf

As far as very low temperatures go, the rule of thumb seems to be - just don't, wait for warmer weather.

The articles say the mortar should be softer than the bricks, so if you've got soft bricks, you need soft mortar, which tends to indicate (1). The articles recommend against cement and against the use of bagged hydrated lime (though I understand it can be OK if it is really fresh). Instead of considering adding cement to speed up setting, consider adding a pozzolan.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135136#Comment_135136 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135136#Comment_135136 Tue, 14 Feb 2012 13:26:53 +0000 Beau http://www.mikewye.co.uk/mikepointng.htm
When re-pointing our barn we did as they recommended and have had no problems. Make sure you avoid frost.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135162#Comment_135162 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135162#Comment_135162 Tue, 14 Feb 2012 17:29:00 +0000 tony
hydraulic lime in tubs is better than bags.

Avoiding cement = avoiding future problems, fast set is not a relevant consideration more so if you cant see it all when finished]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135175#Comment_135175 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135175#Comment_135175 Tue, 14 Feb 2012 18:49:00 +0000 lineweight Posted By: tony fast set is not a relevant consideration

What about the frost issue?]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135179#Comment_135179 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135179#Comment_135179 Tue, 14 Feb 2012 19:43:15 +0000 mark_s
When the weather improves use your new lime putty.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135185#Comment_135185 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135185#Comment_135185 Tue, 14 Feb 2012 23:40:21 +0000 muddy Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135187#Comment_135187 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135187#Comment_135187 Wed, 15 Feb 2012 01:47:09 +0000 lineweight
So the consensus seems to be that putty is better than NHL, and that any kind of mix involving cement is completely out.

Fair enough, but I find it quite frustrating that so much of the advice is stated without anything terribly objective to back it up.

Why exactly is putty preferable to NHL for example? How critical actually is the difference...? several of those articles just make a kind of vague statement that if that's what was originally used, then that's what should be used now, but that in itself doesn't seem to be a particularly logical reason to make the decision.

And as for the inclusion of cement in mixes...so cement decreases flexibilty and breathability - that's fine - but in a mix with a small amount of cement how much impact does it really have? Does it make it 95 percent as permeable or 50 percent as permeable....has any actual objective research been done?

This article is kind of interesting...seems to imply that guaging with cement may be ok in some instances and also makes the point about relative costs of different options.

http://www.ihbc.org.uk/context_archive/63/limemortars/hydraulicity.html

How much of this insistence on, say, the superiority of (expensive) lime putty is drawn from aesthetic preference rather than objective assessment, I wonder.

I'm not in any way having a go at anyone who has posted on this thread by the way....just expressing my frustration as someone who just wants a straightforward, objective answer to a seemingly straightforward question.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135188#Comment_135188 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135188#Comment_135188 Wed, 15 Feb 2012 01:51:06 +0000 lineweight Posted By: muddyI would guess that you want to render the masonry to make it air tight before insulating, therefore its not going to be seen. I would also second that you can soak bagged hydraulic lime in a tub for a month or two, or you can use nhl bagged lime directly. For an internal wall try adding hemp fibre if you have a very irregular thickness, it will stop it cracking.

Not going to render the masonry - it will indeed be behind insulation but the airtightness will be dealt with in a separate layer.

Just need to repoint/repair/replace bricks in a few locations where the brickwork has been damaged or where the mortar is failing.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135189#Comment_135189 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135189#Comment_135189 Wed, 15 Feb 2012 07:15:21 +0000 tony
It keeps the bricks dry too by the same process.

Lime is much better to work with when it is fully hydrated, it will work from bags, cheaper out of bags but sometimes it can be quite old too.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135196#Comment_135196 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135196#Comment_135196 Wed, 15 Feb 2012 08:34:08 +0000 Triassic
I'd suggest you experiment with colour, you'll need to try different types of local sand to get the colour right. I tend to wet the wall using a garden spray as you don't want a dry background to pull too much water out of your mix.

Best keep your mix a little on the dry side, it should be damp and when squezed form and remain in a ball without being wet and slumping. I also us a Churn brush to beat back to mix into the crevises in the wall. I find the finished pointing less harsh (I don't like it too smooth with tool marks) and more textured which looks good against the sandstone rock we have round here.

Do not use red sand and cement, or put cement into your lime mortar mix.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135208#Comment_135208 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135208#Comment_135208 Wed, 15 Feb 2012 10:25:47 +0000 lineweight Posted By: tonyLime pointing is crucially involved in the processes involving moisture in the wall, it sucks up any moisture, water, wet or damp as it is highly hygroscopic and transports that moisture away to the outside.

It keeps the bricks dry too by the same process.


Sure, I understand this, but how much more hygroscopic is it than say a 1:2:9 cement/lime/sand mix? I can't find anything that actually states in figures how much of a difference it makes.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135218#Comment_135218 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135218#Comment_135218 Wed, 15 Feb 2012 12:24:25 +0000 Peter_S
http://www.buildingconservation.com/articles/cement/cement.htm]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135222#Comment_135222 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135222#Comment_135222 Wed, 15 Feb 2012 12:47:02 +0000 lineweight Posted By: Peter_Sthis article sets out most of the points you raised, but if you need more science, then your getting into the building physics and chemistry fields..

http://www.buildingconservation.com/articles/cement/cement.htm

Thanks, that clarifies a few things. Amongst others that a 1:1:6 mix is better than a 1:2:9 mix if you are using cement.

Interesting that it implies that hydraulic lime is somewhat impermeable....although it doesn't state *how* impermeable compared to a cement or non-hydraulic mix.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135223#Comment_135223 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135223#Comment_135223 Wed, 15 Feb 2012 12:47:20 +0000 Dominic Cooney You will find that cement is unnecessary for this job. Lime putty really is easy to use for pointing, I mixed sharp and soft sand with putty, choose the colour of the soft sand to get a good match for the existing (although perhaps doesn't matter if it will not be seen). Once you have tried it you will wonder what all the fuss is about, and will not want to use anything else again.
If you want a quick set, use NHL. I have used it for lime plastering. Goes off quick.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135226#Comment_135226 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135226#Comment_135226 Wed, 15 Feb 2012 12:54:10 +0000 lineweight
http://markbrinkley.blogspot.com/2005/12/why-build-with-lime-why-indeed.html


It sounds just dreadful, doesn’t it. “Major hazard”, “clogging”, “greatly reduced porosity,” “seriously weakened”, “poorly formed pore structure”, “susceptible to frost damage and deterioration.” What a catalogue of woe! What we have here is an attempt to drive a wedge between the purists, who are delighted with the results from the Smeaton Project, and the mixers. But there is something just a little bit too alarming about these findings for my liking. Whilst they may have found segregation taking place on certain mixes, how can they be so sure that all these horrors will result? After all, the test of a good mortar is how it behaves after 50 years in place. The choice of language used by Graham in this piece is, to my mind, a dead giveaway that we are not seeing pure science at work here, with its understated conclusions and room for doubt, but an attempt to rubbish a practice that has been in widespread use since the 1830s.
]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135227#Comment_135227 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135227#Comment_135227 Wed, 15 Feb 2012 12:55:56 +0000 lineweight Posted By: Dominic CooneyI have read that article above before, it is worth reading.
You will find that cement is unnecessary for this job. Lime putty really is easy to use for pointing, I mixed sharp and soft sand with putty, choose the colour of the soft sand to get a good match for the existing (although perhaps doesn't matter if it will not be seen). Once you have tried it you will wonder what all the fuss is about, and will not want to use anything else again.
If you want a quick set, use NHL. I have used it for lime plastering. Goes off quick.

I might give it a go just to see what it's like to work with if nothing else.

What about repair-type work (replacing bricks, rebuilding some areas) rather than just pointing - would you still advocate using putty for that?]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135229#Comment_135229 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135229#Comment_135229 Wed, 15 Feb 2012 13:25:05 +0000 Peter_S
http://www.nrc-cnrc.gc.ca/obj/irc/doc/pubs/nrcc20148/nrcc20148.pdf]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135230#Comment_135230 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135230#Comment_135230 Wed, 15 Feb 2012 13:26:38 +0000 Nick Parsons Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135269#Comment_135269 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135269#Comment_135269 Wed, 15 Feb 2012 18:15:37 +0000 lineweight Posted By: Nick Parsons''Once you have tried it you will wonder what all the fuss is about, and will not want to use anything else again.'' So yes, why not?

Well, the extra cost, mainly, would appear to be the main downside.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135275#Comment_135275 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135275#Comment_135275 Wed, 15 Feb 2012 18:40:03 +0000 Nick Parsons Edit: Google says it's £9 a bag, so read £5 a bag more. It's still not a lot.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135293#Comment_135293 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135293#Comment_135293 Wed, 15 Feb 2012 22:33:47 +0000 Triassic
The use of lime & cement in traditional buildings

http://www.historic-scotland.gov.uk/informguide-limeandcement.pdf

http://cadw.wales.gov.uk/docs/cadw/publications/Tech_Con_2_Lime_Mortar_EN.pdf]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135304#Comment_135304 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135304#Comment_135304 Thu, 16 Feb 2012 01:46:52 +0000 lineweight Posted By: Nick ParsonsIf you use slaked bag-lime (to make your own putty) it will, if I remember correctly, cost you about £2 a bag more than cement. Not a huge deal.
Edit: Google says it's £9 a bag, so read £5 a bag more. It's still not a lot.

Fair enough; it's not a lot extra.

Does require you to be thinking a bit ahead of yourself though.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135310#Comment_135310 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135310#Comment_135310 Thu, 16 Feb 2012 08:54:52 +0000 Joiner
But note the "apparent". I become good friends with a local assistent-CO during his tenure on our patch. He'd done his master's dissertation on lime and took a lot of time to explain in detail why an unadulterated mix was better all round. He didn't lecture in the way that lime purists do when talking to those plebs who lack the capacity to understand natural processes, that capacity which makes them so superior to heavy-handed trades people. (HEAVY IRONY WARNING!)

Of course you can't see what's going on unless you get it completely wrong and you go back the next week to find half the wall on the floor or the next year to find half the wall spalled all to hell. The processes are more subtle than that for all the reasons explained in previous posts - and other threads ad nauseum.

Having said that, the Italians don't seem to be quite so particular. They'll happily bond masonry (brick or stone) in historic buildings with cement and then POINT with lime to achieve the "authentic look". Even in earthquake zones! And they discovered/invented lime mortar!

But having tried it the "proper" way I'm inclined to stick with it now because it's much nicer to use. Significantly, the two "traditional British brickie" guys who've worked with me on a regular basis have, after moaning about "all that twaddle" and how they "couldn't guarantee it" have come around to seeing the sense of it and have actually both said how nice it is to work, to the point where they now recommend lime rendering to all their customers. I won't say anything about how they've also caught on to the fact that they can charge more for it by cashing-in on the premium that attaches to the green-cache. Love it. :wink:]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135413#Comment_135413 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135413#Comment_135413 Thu, 16 Feb 2012 18:40:13 +0000 mike7
I've been very happy with the result - it kept the builders happy at the time as it stiffened fairly quickly, and the strength it eventually developed seems comparable with the original. Could it be that my 5% was sufficient to act as a pozzolan, yet not sufficient to introduce other unwanted characteristics?]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135414#Comment_135414 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135414#Comment_135414 Thu, 16 Feb 2012 18:42:18 +0000 Joiner ]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135421#Comment_135421 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135421#Comment_135421 Thu, 16 Feb 2012 19:13:22 +0000 hairydude
Very helpful bunch and offer a lime matching service - if you take a sample of your existing mortar or render and send it up to them they'll advise on mix and spec to match the existing (can't recall how much it was but I didn't think it was too dear at the time).

They also do a course and have advice notes on working with lime in low temperatures.

Masons Mortar (http://www.masonsmortarshop.com/knowledge/) are a good supplier and have always been a good source of advice (free:smile:) on the use of lime.]]> Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135430#Comment_135430 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135430#Comment_135430 Thu, 16 Feb 2012 19:38:57 +0000 Joiner Repointing/repairing lime mortar: NHL vs hydrated (bag lime)?? https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135464#Comment_135464 https://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=8623&Focus=135464#Comment_135464 Fri, 17 Feb 2012 01:21:33 +0000 lineweight
Anyway, I've got hold of a copy of the Smeaton report and I'm going to sit down and have a read of it and see what I make of it.]]>