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all about building lime

I used to be a girl who knew all about lime; the ones you quarter and stick into the top of a corona beer, the lime that goes in a caipiroska and a caipirinha. The lime that’s indispensable in Thai, Lao and Vietnamese cooking. Even the lime that can be squeezed on oysters, while sipping champagne under a sail of the Opera House and gazing out over Sydney Harbour… sigh…


But now I’m a girl who knows all about the other lime. Building lime. Calcium oxide. Quicklime. Hydraulic and Non-Hydraulic lime. Hydrated lime. Slaked lime, Burnt lime, Fat lime, Lean lime.

Before the advent of portland cement in the mid 19th century, it was lime that held together buildings made of stone and brick. While the wholesale adoption of portland throughout the world practically shelved the use of lime mortars, lime is now making something of a comeback.

These days, lime mortars are primarily used in the restoration of historic buildings; where they are compatible with the existing mortar, they blend in terms of texture and colour to the original, and the flexibility of lime accommodates the softening or weakening of old bricks and stone and does no further damage to them.

Scientific and academic interest in the history of construction history and the efficacy of modern materials has also had an influence on lime’s recovery. We now know a lot more about the chemical properties and reactions at work when using various building materials as a result of studies and testing at a scientific level. For example, due to the worldwide concern about the environment, researchers tell us that lime creates very little CO2 in production compared to portland cement, and this subsequently opens the door to its use as an eco-friendly alternative.

brickies sand

In my case, there are several reasons to consider using lime.

Firstly, portland is too hard for schist-stone and your mortar should never be harder than your building material. Secondly, it’s incompatible with the existing material: You should repoint like for like, if possible. The house was built entirely with a clay mortar. Clay absorbs and releases moisture, it’s highly flexible and highly permeable. Cement is the exact opposite. Using cement on the outside of a clay filled wall would potentially result in cracking of the cement pointing as the rest of the building heaves and shifts. Probably it would trap moisture inside the walls and cause saltpetre and other moisture related problems. But lime, on the other hand, is like clay, flexible and breathable.

So, where do I start? There is not just one type of lime or one standard recipe. So I’ve been trying them all.

At first, due to some translation/linguistic ‘nuances’ (dictionaries can only do so much – check out the list of words for lime in English in the 2nd para, and then times by three to get the Portuguese variations… then you add complications like the similarity of ‘hydraulic’ and ‘hydrated’ and all this results in is a blank stare from the guy at the shop) the only lime I could get my hands on was quicklime. ‘Cal vivo’ in Portuguese.

Quicklime needs to be slaked, i.e. mixed with water and then left to ‘fatten’ (ferment, say) for anything up to 6 months before it is used. Oh bummer. But fortunately there are plenty of ‘skip the rules’ DIYers on the internet offering up all manner of experimental alternatives, so I aligned myself with them to start with.

bubbling quicklimebubble

First I made up ‘hot lime’ and cement mixes; i.e. straight from the bag 1:1:3 lime: portland: sand. At this stage I’m using brickies yellow sand, not ideal for mortar but a nice colour. This is too strong a mix, and it’s a very dodgy way to use the lime, but it results in an aged patina (probably because it’s burning the stone as it reacts) that looks really good. This mix wont work for the engineer though, who’s also the ‘responsavel de obras’, the inspector. It’s too unorthodox and it will probably all fail anyway.

So then I slaked the lime for 24/48 hours. There are a few ways of slaking. Firstly you can use about 1:1 water, and this does a crazy thing of drying to a powder after giving off a lot of heat. That powder is now called hydrated lime (cal apagada). Better still is to use a 2:1-4:1 (depends on the quality of the lime – I find a 2.5:1 a bit stiff and 3.5:1 nice and workable but maybe a bit weak) and this turns into lime putty… after a really fun volcano-like eruption… stand back while watching this movie!

The third slaking method, a very traditional one taken from The Art of the Stonemason by Ian Cramb, is to mix the quicklime with damp sand, 1:3, and turn it over occasionally over 6 weeks. I’ve got this going on as well.


A word of warning though: I had been fiddling about with the quicklime for a few weeks with only casual regard for safety. One day I was turning over the sand-lime mix in the box for just for a couple of minutes wearing a t-shirt. There was no visible powder on my skin, but I washed my arms off with soap anyway. An hour later I was covered in blisters, including my shoulders – it even went through the t-shirt! Not good. But fortunately I’m not quite so stupid not to wear goggles and mask because I could’ve been blinded! Now, several weeks later, every time I go out in the sun, I get blisters. Nasty stuff.

The putty (even slaked for this ridiculously short 24 hr period) makes your mortar really nice and sticky and easy to work with. Even mixed with grey portland, (1:1:6 is the correct ratio – according to CSIRO – very reliable) over several weeks it dries to a bright white. I also did a few mixes with one part clay in the mix, clay that came out of the original wall. This resulted in a better colour, marginally, but more on clay later.

So far all of these mixes contain cement, which for new wall building will be fine, provided the mix isn’t too strong, and I can get the colour right. But for pointing old walls, this needs a pure lime and sand mix. Slaked quicklime/sand mixes are, these days, only recommended for interior pointing because it is so vulnerable to the elements while it takes years to harden. So I moved on to Hydraulic lime.

The term ‘Hydraulic’ (or ‘non-hydraulic’, as quicklime is) refers to the lime’s ability to set under water, or not. Hydraulic lime sets when combined with water, therefore it dries hard quickly, like cement does. Non-hydraulic limes stay soft initially and gradually harden over a longer time.

There are three types of Hydraulic lime, basically weak, medium and strong (or #1, #2, #3.5 and #5.) The strongest is almost as strong as cement, so it’s usually only used for building areas subject to harsh conditions such as by the seaside, or chimneys, or window sills. But what do you know, #5 seems to be all I can get here in middleofnowhereedgeoftheoworld, central portugal. The #5 is a horrible grey (3.5 is white, I believe) so I’ve done some colour experiments: This time I’m using river sand (a greyer sand with larger particles.)

lime test wall

What do you mean you can’t tell the difference? On the left is a straight Hydraulic:Sand mix at 1:3. Horrible colour and horrible to use. None of the nice stickiness of the putties. In the middle is 1:3 plus 5% ferrous oxide for colour. Still horrible but slight improvement. On the right is .5 hydraulic: .5 sand slaked quicklime, : 3 river sand, 10 % ferrous oxide. Getting closer, but still horrible.

So where does that leave me? Hydraulic too strong, too grey; Non-hydraulic too weak, too white. I think I have two more options.

The first one is pozzolans. They are additives that make non-hydraulic lime harden like hydraulic lime. They can be bagged powders like Brick dust, Fly Ash, or fired clays as found in Pozzolan, Italy. There are proprietary mixes like Metastar. But can you get them in Portugal? My hardware supplier has never heard of a pozzolan, and all I get from google is one academic who mentions “nationally produced” pozzolans in a paper. I’d better send her an email. Maybe she’s my new best friend.

My other option, as some of you may have been thinking, is clay. If lime can make a comeback why can’t clay? If my 5 metre tall walls are still standing after 70 years, why can’t I apply the “like for like” rule and repoint with clay? I’m not suggestion that I dig it out of my garden like the old boys did. I don’t mind buying some peace of mind in a bag. And more… there’s actually a company in the Algarve, Construdobe who produce clay mortars… it’s sounding like a solution, isn’t it? If only my engineer can be convinced…

to be continued….


  1. Tessa April 12, 2009 5:23 am Reply

    I am confused – where does lime go – on the outside or inside walls?

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  2. sophie April 17, 2009 5:46 am Reply

    like you, i’ve used lime lots with only a casual regard for safety. i’m about to make some lime putty tomorrow (for limewashing the new kitchen wall) so think i better goggle/glove-up after reading about your blisters. hope they’re better soon.

    i’m always amazed by the shop assistants in the diy store who seem to have a total disregard for safety when weighing out cal vivo – they just shove their hands in the stuff. eek!!

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    Emma   Reply: April 19th, 2009 at 10:00 am

    I know what you mean! Sacks with holes, stuff spilling everywhere, they’re breathing it in…. aghhhhhhh! It’s the blindness that I’m paranoid about now… I wear swimming goggles!

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  3. penfold May 10, 2009 7:33 pm Reply

    Hi Emma, nice blog and good to see someone else stressing to get their render right!

    We use a weaker mix (1:1:8) hydraulica:cemento:areia with just a cup of oxy-ferro (yellow). The sand in 50:50 Rio Tejo (gives a good texture) with Rio Maior (which is bright yellow and overpowers the cement).

    It takes a few days to go off when it’s weaker but does go hard enough for pointing and gives a better colour.

    Hope this helps. Please feel free to tell me to bugger off if not 😉

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    Emma   Reply: May 12th, 2009 at 2:53 am

    Nothing is more welcome than educated advice! Most people just say things like “careful that wall doesn’t fall on you”… good to have a rock handy to chuck at people sometimes… I’ll ask around about those sands; I really would like more grit… and yep – the yellow+ferros is coming close to the right thing… there’s a new post coming up…thanks again, good to find someone living on the same planet 🙂

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  4. Wendy May 28, 2009 3:25 am Reply

    Great post! The devil’s in the detail and this is brilliantly satanic stuff. Since I’ve just set off down much the same road, working with schist as well, having this to chew on is fantastic. Thanks.

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    Emma   Reply: May 29th, 2009 at 12:24 am

    Thanks! This is the stuff I’m really interested in… but I have friends who are so bored everytime I go on about my mortar quest… good to know someone out there appreciates it!!! I think I’ve found the right recipe for me, will post it shortly.

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  5. Isabel June 25, 2009 3:05 am Reply

    Check this out, it might be useful, who knows (certainly not me):


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  6. Isabel June 26, 2009 9:46 am Reply

    Mmmmm… I thought I had posted here this link, in case it is of any use:


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    Emma   Reply: July 20th, 2009 at 3:28 am

    re Fradical… awesome! thanks – great find. thanks for passing on. 😉

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  7. Isabel June 26, 2009 4:36 pm Reply

    Ooops! I had!

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  8. Derek September 30, 2009 11:52 pm Reply

    Thought you might like this Emma. Looks like you are at the cutting edge of the lime rendering world.


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  9. rick October 21, 2009 9:18 pm Reply

    hi emma,

    like your site. sassy.

    anyway, we often use 9,2, and 1 (9 sand, 2 (hydraulic)lime, 1 cement) or (13, 3, 1) which with a nice yellow sand, (you can get it here if you shop around), both give a nice creamy mix, structually sound, aswell as more permeable and flexible than a pure cement sand mix. creamy is the texture you’re after, whatever your mix. whether rendering or laying, laying wants to be a bit stiffer thou. if you want only to change the color not the physical properties, you can try getting hold of white cement (this keeps it closer to the color of the sand) back in the uk this costs a fortune (about £30 a bag – 25kg compared to £2.50 for opc) can’t imagine it’d be any cheaper here, since a lot of building materials are even more expensive.

    for rendering outside you want sharp sand, and inside sharp on the scratch coat, or 50/50 to give it some body and soft sand on the top coat.

    when you use cement use a feb agent, and if you are using cement in a render outside you need to use a frostproof additive. you can find both of these in builders merchants here.

    i liked rendering with quick lime mortar (putty), it has a whole other feel, and on historic buildings it is nice to know you aren’t harming them but are building in harmony and sympathetically with the existing materials and are somehow connected to the past by the work you are doing. it being the same as the original work to the house maybe hundreds of years ago. even more so with carpentry.

    on pure lime mixes, pozinans are a good idea, and if you are rendering you need to mix in some animal (pref. horse hair) old recipes also used to use cow shit as you would use feb in a cement mix to make it creamier still, which allows it to run better.

    sack cloth, (heavy natural fiber cloth like hemp, it needs to breath, or you could use ground cover, as its permeable) is a good idea to cover your work to prevent it from, a drying out too fast, b, from getting washed out by rain, or c, frost damage. leave a couple of weeks between your scratch coat of render before you put the top coat on. whats good about natural fiber cloth is you can soak it to help prevent drying to quick which causes cracking (which you dont want).

    something else that helps are good tools, sprung trowels, wether bricklaying or plastering trowels, pointing or gauging trowels. it does make the application that much easier and nicer. as does a good plastic hawk that doesn’t draw too quickly. ebay’s a great place for 2nd hnd tools with loads of life left in them, or new tools at a better budget than tool prices here in portugal, which i have to say are shockingly expensive and crap, to put not too fine a point on it. look out for spear and jackson, marshal town, and tyszack. honing down a gauging trowel out of rounded end, into a point is also worthwhile for repointing stone.

    oh yeah and wear a long sleave shirt and a pair of gloves if you dont wanna get burned. nobody wears goggles thou, feel the burn.

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    Emma   Reply: October 21st, 2009 at 11:49 pm

    Guru rick, thanks for all that, very useful and interesting. If it wasn’t raining I’d be out there mixing up a batch right now… but very good to hear from others going the lime route, and sharing the wisdom.

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  10. Andy Copus March 20, 2010 9:29 pm Reply

    Hey how you doing, finding this all very helpful, can you tell us what the building inspectors thoughts on your using clay mortar and also is it expensive stuff if you don’t want to go digging in the garden?

    Thank you kindly

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  11. Cyril April 2, 2010 7:37 am Reply
  12. Pointing mortar June 23, 2010 8:56 pm Reply

    Under no circumstances use pva on a mortar for outside the building unless you use the waterproof type ( even then the jury is still out as to whether it is of any use or just an added expense). Your standard pva turns to a gel in extremely wet conditions, even when mixed into a mortar, that will break down the mortar if it freezes. it is bad enough pointing a house once without having to redo it again 5 years down the line.

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  13. Ceres February 28, 2012 12:13 pm Reply

    Fradical sells ‘Aditivo Pozolânico’ and Uniao de Gessos in Lisbon has all you need to work with traditional lime. They are the suppliers of many renovation projects in historical buildings in Portugal ( that’s how I heard about them). Secil Portugal has NHL5 e NHL3.5 ( give them a ring!) e Secil is a lime supplier of Mikewye and Associates Ltd in England ( who specialize in Period House renovation). I did my lime rendering course with them. If you speak fluent Portuguese ( and I am sure you do) , it’s easy to source building materials in Portugal…just ring around and you’ll find what you need. ‘ Quem tem boca vai a Roma’ lol

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    Emma   Reply: March 1st, 2012 at 10:40 pm

    superb info my fellow third way restorer. you are right up my street, so to speak. thanks.

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  14. Ceres February 28, 2012 12:21 pm Reply

    My interest is in the renovation of traditional Portuguese houses and I hasten to say, NO CEMENT please! I have seen enough period houses ravaged by modern builders in the UK and cement renders always seems to play a part…and other silly non-breathable’ materials and unsympathetic techniques! I don’t know if you have an old house but…

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    Emma   Reply: March 1st, 2012 at 10:38 pm


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  15. Picture Framing Milton Keynes July 31, 2012 9:43 pm Reply

    Nice one emma, great blog. Even the comments in this blog are helpful. Wish me luck with my new projetct. Why do I get the feeling its all gonna go horribly wrong?

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    Emma   Reply: July 31st, 2012 at 10:08 pm

    Only small things go wrong and there’s almost nothing that cant be fixed. Although my windows are a big mistake, come to think of it. Iive been thinking about a Lime:Part Two because now I’ve put my theories to work and used the limes every which way I’d kinda like to report back that IT REALLY IS THE BEST STUFF, but I wouldn’t bother doing my interior walls in it again. Too much work and now I want my walls straight not wavy as they catch too much dirt. There, post written. Good luck adamjohnsmith, trepidation is only excitement in black clothes. Go forth and build!

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  16. Linda Vieira August 3, 2012 10:20 pm Reply

    Hi Emma!

    I really enjoyed reading your story, and I am even more pleased to let you know that you can now find Natural Hydraulic Lime in Portugal. The real thing! Without any additives, just the natural and unique result of burnt limestone. Our NHL’s were certified last year according to the new EN459-1:2010, which does not allow any additions or gypsum to be added to the process. We also have NHL 5 and NHL 3.5, which is less strong, and has a beautiful creamy colour! We have also developped a natural hydraulic lime based render, with natural cork aggregates! So besides having a light weight render, you have a thermal and acoustic improvement in your home as well. If you want to know more also about our new line of ecobuilding products, just let me know! I’ll be glad to send you our brochure on sustainable building. We are also working very strongly in the UK. You can take a look at our supplier’s site, and see what we’ve been up to: http://www.mikewye.co.uk.

    Hope you like it! Let me know if you’d like to test our products. I’ll be glad to send you a sample!

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  17. João Carlos February 2, 2019 2:47 am Reply

    Bom dia Emma 🙂,

    Five years ago, I lightly experimented with red clay, Cal, and Wattle fibres, for constructing bungalows in Hogsback South Africa.

    I am currently contemplating building beachfront bungalows in Moçambique, for tourists, but using large building blocks set directly upon walls, purely of plentiful beach sand and Cal, (no stone, possibly with glass or grass fibre, and preferably without water, using readily available warm tropical humidity,) any suggestions on the type of Cal to use, and proportionality of beach sand?

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    Emma   Reply: February 3rd, 2019 at 12:31 pm

    @João Carlos, I’d be researching the effect of the salt in the sand… and if it’s for tourists how you’d get permission for them as dwellings if it’s as unconventional as it sounds. Interesting, good luck.

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