Lime Discussion

[MdB]

A new thread to carry on the discussion from this thread:
http://www.periodproperty.co.uk/forum/viewtopic.php?f=1&t=11156

Okay,let's try and start from the top but chances are I'll answer the questions not in order,I do suggest you read this though.
http://www.amazon.co.uk/Building-Lime-Introduction-Stafford-Holmes/dp/1853395471

I'll see if I can borrow a copy. Thanks for the link.

it always has been and all my mates in the trade do it that way as well and nothing has fallen down yet

That's the excuse used by people who have either never used lime or don't want to,they've only used cement and it works perfectly well for them and gets the job done.

Too true, hence my caveat.

6:1:1 mixes are fine if you want a strong mix but 3:1 lime mixes with a couple of handfuls of cement are a bad idea as the cement clumps making the mix weaker than without it. How do I know this? well somebody has tested it and the results are published.

I'd recheck that if I were you,published where exactly?
And who tested it?
Wasn't that Tommy off the telly was it :roll:
April fools day is long gone mate!

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

I agree with you here, (apart from the lumps which I've never noticed) however, the question is "how quickly does it carbonate in the bag?" I do not know the answer to this (and would be interested in knowing it) blue circle give a lifetime of 3 months+ for their hydrate and I know that my local builders merchants gets a new pallet of hydrate every two weeks. I would therefore expect a bag of hydrate used within a month to have very similar active lime levels to that of putty. Any unused lime should be converted into putty of course for it to keep. Exactly the same process applies to NHL limes which will also carbonate in the bag. Some lime producers state that they will keep for 1 year in the bag so again the process must be slow.
From this, I conclude that there is no technical reason not to use hydrate. In my very limited experience have also not noticed any difference in workability between hydrate and putty and as hydrate is cheaper, unless given a good reason not to, I will continue to use it. I very much welcome comments on this.

I thought I explained that,you obviously weren't paying attention.
As soon as it's hydrated.

You have missed the point. The hydrate I have is 93%(minimum) active lime. If this has reduced to say 90% after sitting in the bag for 3 months due to the carbon dioxide that has leaked inside the bag then this will make no difference at all to the quality of the lime mortar made from it. If it instead goes to 50% active lime after one week then this is significant and a good reason not to use hydrate. The manufacturers claim otherwise though.

You choose who you want to believe,a builders merchant who sells cement and the salary men at Blue Circle,neither of whom would know how to use lime if it climbed up their company uniform trousers and bit them on the nadgers.
Or a lime practicioner.
Your choice.

The manufacturers of hydrate and NHL state that it should keep in the bag for 3 months+. You seem happy to use NHL so why not hydrate? As far as I can make out, NHL is very similar to hydrate apart from the additional chemicals in NHL. Both will carbonate in the bag I believe so why the different attitude to them?

unused lime should be converted into putty of course for it to keep

:lol: ;I
I think I just broke some ribs laughing.

Laugh at me all you want, I don't mind but please let me know why you are laughing so that I can learn.
If I buy a new bag of hydrate and use only half straight away then the other half will be unusable a year later. If it is turned into putty though and kept damp, carbon dioxide can't get to the putty so it will keep. What have I got wrong here? (and it isn't just me - nobody on this site as corrected me on this before)

I, like most people here I guess, would have said that NHL 5 is stronger than NHL 2 (indeed the number refers to its compressive strength

Yes NHL 5 is stronger than NHL 2,eminently versus feebly hydraulic,with NHL 3.5 being moderately hydraulic.
But no,the numbers do not apply to its compressive strength.
They refer to the natural impurities in the lime,i.e. clay that aids setting.

NHL limes are classified according to Compressive Strength expressed in N/mm2 measured @ 28 day in mortars prepared with a 1:1 binder/sand ratio as defined by EN 459.
http://www.stastier.co.uk/nhl/info/eunorm.htm

There - you have learnt something today. Now can you please teach me where I'm going wrong.

 

[Gervase]

The Holmes and Wingate book is an absolute must if you want to understand the mechanics of building limes - and it's also a fascinating read. The Building Limes Forum, of which Stafford Holmes is a founder member, is also an excellent source of information and advice on lime, and well worth the membership for the quarterly newsletters and annual journal alone.

As for carbonation time for bagged lime, if you've got some bags, get hold of a simple indicator - phenolphthalein is the best - and use that to test for reactivity. I've found that by dragging up my A level chemistry titration principles from the depths of an addled brain, I was able to ascertain that Castle hydrate, unopened, kept around 90 per cent of its hydroxide make-up after three months. That is fine for home-made putty for pointing or plastering.

I haven't kept any for longer, so I can't tell you how the reactivity falls off after that, but I imagine in an unbroached bag it would be a slow and steady curve, much like the carbonation of mortar itself. A while back I broke open a lump of 3:1 fat lime mortar the size of a cricket ball that I'd made two years earlier, and the core was still completely uncarbonated, turning dark pink with the phenolphthalein (showing that the pH was still around 10 or 11).

That said, you will always get a better mortar/plaster with putty, and the very best is stuff that you knock up twice. I do the basic mix in a roller mill and then knock up each load as required in a drum mixer, and that gives a lovely sticky mix or (with more water) a plaster that flies off the trowel and sticks like snot to an oven door.

As was mentioned earlier, you will often have to add water to a putty/sand mix, but do so sparingly and only after the putty and sand have been thoroughly mixed, as lime putty is slightly thixotropic, and the more you bash it, the 'wetter' it becomes.

 

[MdB]

Thanks for that Gervase - that makes sense.

The double mixing is also something I've learnt to be essential though I use a paddle mixer for the second go.

 

[worms]

The other lime thread was interesting but I think we need to recognise that there can be a quite rational explanation for the difference of view between the professional builder and the enthusiastic amateur. It is a balance of risk and cost.

The builder does not want the risk of material failure and can transfer all the cost of this across to the client. If he has to re-visit the client to put things right he bears the cost. So in this scenario, an occasional bag of carbonated hydrate is not worth the risk.

For the amateur, the opposite is true. Since hydrate is so cheap relative to bought-in putty and the risk of a bad bag seems to be low (but perhaps not negligible) then, for some jobs, the balance is in favour of using hydrate and accepting the occasional failure.

The professional builder will, of course, do what all builders do and dogmatically claim that there is only one way to do things and anyone who expresses any other opinion is a clueless amateur. Which is also one of the reasons that so much lime has been replaced by cement…

 

[OddJob]

Thank you Gervase and worms,you answered all the questions better than me and saved my typing finger
MdB,I would give you one further piece of advice,don't believe all those articles you find.
Forums like this and the building limes forum are far more reliable for honest advice and information :wink:
Andy

 

[MdB]

It would be nice to know your reasons for laughing at the idea of making putty from hydrate if you would be so kind.

For those where the customer is paying, I can understand why you would just buy the putty but for the rest of us, I see no major issue with doing this.

It is a subject that comes up regularily here with lots of advice being given on the subject by lots of people. If there is an issue, I am not the only person that would like to know.

 

[Schoolmarm]

I agree,no matter how much I read, I need to know more.

 

[OddJob]

The question has already been answered by worms.

The builder does not want the risk of material failure and can transfer all the cost of this across to the client. If he has to re-visit the client to put things right he bears the cost. So in this scenario, an occasional bag of carbonated hydrate is not worth the risk.

There's an old carpenters saying,"measure twice,cut once".
When I first started out in lime on rainy days I'd mix different mortars and store them away,labeled,to go back to six months later,I wasn't the only one doing this.
Hydrate always gave a weaker mortar with far greater risk of failure.
Also at the time a leading lime putty producer was using hydrate to produce putty,it was removed from the shelves of all the suppliers and mortar manufacturers I knew at the time because of failures,there were just too many complaints.
In 15 years of lime work I've had two failures,both very early in my lime career and my first two lime jobs,one was down to that paticular brand of lime putty using hydrate,the second was due to gauging lime mortar with cement for a chimney flaunching,this was done because at the time the hydraulic lime supplier was having bagging problems and the lime was going off in the bag.
The first job was pointing and re-done by me at 20-80 expense by me and the supplier of the lime,he bore 80% of the cost,I accepted 20% which I paid for with my labour because part of it was my fault,it was my first lime job and it was in hot weather,I failed to spray mist the work and cover it in damp hessian properly so it carbonized too quickly.
The chimneys were re-flaunched about five years later entirely at his expense using hydraulic lime.
I won't use hydrate older than one month and still only as a plasticer with hydraulic and hydraulic I won't use older than three months,hence for large jobs I always under order,I can pick up a few fresh bags later.
Putty on the other hand will keep for years,I've got one very special tub of 10 year old chalk putty in my garden I dig into from time to time,it just gets better with age.
Your quote,

6:1:1 mixes are fine if you want a strong mix but 3:1 lime mixes with a couple of handfuls of cement are a bad idea as the cement clumps making the mix weaker than without it. How do I know this? well somebody has tested it and the results are published.

You quoted this article,
http://www.buildingconservation.com/articles/cement/cement.htm
I remember it well and the project,check the date,it was 15 years ago,1995,the year I started in lime,within a year opinions were changing and have changed several times since,and the opinion is now very firmly against any gauging with cement.
Around the same time there were debates about gauging putty mortar with hydraulic or vice versa,now gauging putty and hydraulic is perfectly acceptable,putty as a plasticiser in hydraulic mortar or hydraulic in a putty mortar as a setting agent.
This has come about by people who actually use the stuff day in day out,not people who sit behind a desk working out equasions and producing articles based on assumptions.

NHL limes are classified according to Compressive Strength expressed in N/mm2 measured @ 28 day in mortars prepared with a 1:1 binder/sand ratio as defined by EN 459.
http://www.stastier.co.uk/nhl/info/eunorm.htm

There - you have learnt something today. Now can you please teach me where I'm going wrong.

Nope,sorry,I learned nothing new from that.
Hydraulic limes compressive strength and setting ability still comes from it's various impurities.
Read the Holmes/Wingate book and you will see how it was used in building major canals.
Teach you where you're going wrong?
Easy,come and spend a day on site with me on an appropriate job and I'll show you.
I recently had a surveyor ask me similar questions in an email expecting free advice.
I told him to come and work with me for a day and he did.

Please remember I work at it not play at it so work with the materials I trust.
I've been a bricklayer for 32 years,in 1995 I was on the verge of giving up because I was tired of modern building practices,long story but I was on the verge of going off to train young offenders in brickwork,I'd already been accepted to train as a probation officer after the home office decided they wanted real people not half arsed graduates.
Then the client on what I'd already decided was going to be my last building job introduced me to lime mortar,she wanted the back of her house pointing,all I knew was weatherstruck and was going to use a cement/hydrate mix,she'd only called me in to compare prices with other quotes the decided she wanted me to do the job,I knew nothing about lime but picked it up in minutes and I've gone on from there.
I went to uni in my 40's(part time)to study building conservation but learned little I didn't already know,not the tutors fault,they wanted to teach but the uni geared the course down to suit the money they wanted to rake in,so I quit in my third year.

One thing I have learned though.
I'm too flipping old to lay ragstone anymore!
I'm doing that at the moment and it's knackering me.
I remember when I was doing lime work on a castle and the stonemason asked me if I wanted to train up as a mason,I said,
"Nah mate....the bricks are too big!"
:wink:

 

[MdB]

Thanks for that OddJob, very interesting, especially the insight into failures. Knowing where you can go wrong is the first step to avoiding doing the same.

Thank you also for the offer of showing me how to do it on site. If I was a little closer to Hastings then it would be something I would have taken up. I've done the Mike Wye lime course and learnt a lot but there is a limit to what you can gain in one day in an artificial environment with 20 other people.

I live in Cornwall, about 50 mile round trip from the nearest NHL/putty stockist. At £10 per tub plus delivery it isn't cheap for putty. A 25Kg bag of hydrate available down the road is £8 and is about equivalent to two tubs I think. You can see the appeal for hydrate when you are using small amounts.

A quick summary of the points made by everyone I think is in order:

• Putty won't go off in the tub and will keep indefinitely.
  
  Hydrate and NHL can carbonate in the bag or when opened. In the bag is should last something like 3 months whilst when opened it will only last a matter of days.
  
  The quality of NHL manufacture / distribution / storage is considered better than hydrate but both can fail on occasions.
  
  It is worth testing carbonation levels of Hydrate / NHL before use (this is something I want to look into further).
  
  The pros use putty / NHL but don't use hydrate due to the risk it may have carbonised.
  
  There is nothing wrong with using hydrate instead of putty AS LONG AS it hasn't carbonised before use.
  
  Hydrate can be turned into putty once the bag is opened to enable it to be kept. If the hydrate has been carbonised before it is turned into putty then the putty will suffer from this too.
  
  Mixes produced with long matured putty are "better" than mixes produced with hydrate. "Better" means workability / stickness. (I would love to do a double blind test on this...)
  
  NHL number is its compressive strength expressed in N/mm2. NHL gets its strength from the additives in the lime.
  
  Adding some lime to a cement mix is acceptable as a plasticiser. 6:1:1 mixes are just about ok.
  
  Mixes with more lime than cement are likely to fail due to clumping of the cement. Adding a small amount of cement to a lime mix is strongly not recommended.
  
  Adding hydrate / putty to NHL is acceptable to improve workability as is adding NHL to hydrate / putty to improve is strength.

Corrections please (with explanations as to why).

You may not like too much people with their books and calculators with your preference being teaching on the job. Nominally, I would agree with you - I am sure that this is the better way. Unfortunately, this hasn't and isn't happening and an awful lot of knowledge has been lost. To be able to pass as much information on to the next generation as possible, I believe that getting information onto the web before it is lost is very important as this is the way it is going to be accessed in the future. For this reason I think sites like the PPUK site are very important and act as a great resource. I am sure people with the knowledge such as yourself find answering all the stupid questions a pain but if people like you don't, it will be lost forever.

NHL 5 is stronger than NHL 2 (indeed the number refers to its compressive strength

But no,the numbers do not apply to its compressive strength.

NHL limes are classified according to Compressive Strength expressed in N/mm2

Nope,sorry,I learned nothing new from that.

I'll let you get away with that ;-)

 

[OddJob]

There's no such thing as a stupid question,only stupid answers
Having said that I once spent an hour telling a conservation officer and his young trainee about the three different mortars we were using for different jobs on the same property,a lime putty mix,a hot mix,(quicklime slaked with the aggregate)and a hydraulic mix.
He suddenly got this very vacant look and said,
"Yes,but how much cement do you put with it?"
:shock:
I don't find answering questions a pain at all,none of us know everything.
My personal field of so called expertise just happens to be lime mortars/plasters and traditional brickwork so I stick to methods I've tried and trust.
Anything else I just know the basics of.
If you're set on using hydrate then buy it fresh on the day would be my advice,make your putty and mature it in tubs,when you come to use it pour off the lime water into a clean bucket,this is fantastic for when you need to add water to the mix.
Knock up your mix and let that mature a while,I favour storing it in heavy duty plastic builders sacks rather than tubs,squeeze the air out of the bag,twist the top and seal tightly with a cable tie,trust me it's way better than using a fresh mix,I like it at least a week old but even better a month old,doing this lets the lime particles coat the aggregate beatifully and you'll notice the difference,when you need to use it just stir it up and you're ready to go.
If you're using it for haired plaster you can store it with the hair in but I'd use it inside a month-six weeks as the hair rots away in the wet pug,I prefer to mix hair in on the day of use with a larry or in a mixer but ready haired does save a lot of time.
I take your point about the cost but for me it's the quality not the quantity.
My reputation would be up the chimney if I used hydrate :shock:
Besides I buy most of my putty mortars and plasters ready mixed,I used to make it for the company that supplies me when I was their bricklayer and I used to slake their lime so I know how it's done,what goes in it and who mixes it.
Yes I may be biased towards their products but I've tried it from suppliers all over the country and for me nothing comes close.
One thing I will say,I used to be very anti Metastar until I used it on another bloody ragstone wall,I hate that stuff but Kent is full of it
Anyway my client had been on a lime course and insisted on using it with putty instead of a hydraulic mortar.
I have to say it gave a very good setting mortar that was flipping hard!
Too hard for many applications but ideal for Kentish rag and would work well on flint walling which I love.

 

[Ushy M]

Hydrate and NHL can carbonate in the bag or when opened. In the bag is should last something like 3 months whilst when opened it will only last a matter of days.

Sorry if this sounds dim, but does that mean that bags of NHL left lying unopened for 2 years will have 'gone off' and be no use? (We have some - ahem, 7 bags actually left over from repointing the gable end and were hoping to use it to repoint the front of the house).

 

[Gervase]

The only way to be certain would be to test the reactivity of the stuff. Get hold of an indicator which will flag you a pH of 10-12 and test the powder. If it is still that alkaline then it hasn't carbonated. If it isn't, and the pH is below, say 9, then bung it on the garden.

 

[Flyfisher]

Interesting thread. It's easy to understand why cement mortars and gypsum plasters are so popular in the building game!

My turn for some daft questions, if I may:

First, what are the consequences of using hydrated lime that has become 'stale' and partially carbonated?

I've previously mentioned that I've had had some areas of lime mortar spall badly over winter, particularly along the edges of roof tiles and some (but not all) ridge tiles, even though the work was done in the summer and the mortar must surely have been thoroughly dry by the time the frosts affected it. In this application the spalling is not really a structural issue, but it is visually bad and needed to be raked out and replaced.

Could this spalling have been the result of using stale hydrated lime, or might it still happen with a putty-based mortar?

Second: I'm going to be re-laying a path of old bricks that have been displaced by tree roots and general subsidence. Fortunately, the bricks had been bedded into a very soft mortar, presumably lime, and have been fairly easy to clean. I have a few bags of un-opened hydrate from before winter and I'm ready to finished the path now that Spring has truly sprung. So, should I use my 4-month old hydrate for re-bedding the bricks and what would be the best mix?

Even if the hydrate has partly carbonised within the bag, would it really matter in this application anyway? The mortar only really has to hold the brick in place.

I would still brush a dry mix (using fresh hydrate!) over the bedded bricks to grout them.

 

[stephenh]

Well – for what it’s worth I will join the fray…

In the Sth of France two years ago – no putty locally but lots of fresh Hydrate.

So…bought ½ ton hydrate, date stamped and less than a month old, plus 4 big dustbins , mixed (with an electric drill paddle mixer) the lot up with too much water, lids on the bins and taped them up.

Got on with the undercoats which were 3.5 hydraulic lime and hemp – all on a straw base.

This was in May and the local plasterers ( who all used hydrate when they had to) told me that June to September was too hot for any limework.

Went back in October ( by now the hydrate had been soaking for 4 mths) with 2 tubs of 3 mth old putty from the UK.

I cannot, in all honesty, say that there was any difference in the way they handled and 2 years on there is, as yet, no sign of cracking, lifting etc. ( fingers crossed !!)

Yes , putty is preferable, but when there isn’t any at an economic price then I would happily use very fresh hydrate with a good soaking.

He ducks back down behind the barricade…..

 

[MdB]

Hydrate and NHL can carbonate in the bag or when opened. In the bag is should last something like 3 months whilst when opened it will only last a matter of days.

Sorry if this sounds dim, but does that mean that bags of NHL left lying unopened for 2 years will have 'gone off' and be no use? (We have some - ahem, 7 bags actually left over from repointing the gable end and were hoping to use it to repoint the front of the house).

Some NHL producers claim their lime will last a year in the bag unopenned so it may be ok but equally it might have carbonated. As Gervase has said, you need to test though I think I'm correct in saying that this will only check the lime carbonation. NHL also contains various additives which cause it to set when wet and gives it its strengh. I don't think a pH test will check those. For repointing, I guess the strength isn't that important so the pH test might be enough.

 

[OddJob]

Flyfisher

First, what are the consequences of using hydrated lime that has become 'stale' and partially carbonated?

Quite simply that you have less active lime in the mix than you think resulting in a feeble mortar,the carbonized lime has already completed the lime cycle.

Could this spalling have been the result of using stale hydrated lime, or might it still happen with a putty-based mortar?

Yes and maybe.
Putty mortars shouldn't really be used in roofing applications anyway such as pointing eaves,bedding ridge tiles,chimney flaunching and fillets.
Anywhere that exposed that can have heavy volumes of water running off can erode a purely putty mortar very quickly.
Hydrate I would never use on a roof,you're asking for trouble.
You need to use hydraulic lime or a putty mortar with a pozzolan.
The "additives" in hydraulic that MdB refers to are impurities in the lime such as clay that is burned with the lime to create a natural cement.
You say you did the work in the summer,did you keep it damp and covered as it cured?
Not that it would have made much difference if you used hydrate which is not up to the job.

Second: I'm going to be re-laying a path of old bricks that have been displaced by tree roots and general subsidence. Fortunately, the bricks had been bedded into a very soft mortar, presumably lime, and have been fairly easy to clean. I have a few bags of un-opened hydrate from before winter and I'm ready to finished the path now that Spring has truly sprung. So, should I use my 4-month old hydrate for re-bedding the bricks and what would be the best mix?
Even if the hydrate has partly carbonised within the bag, would it really matter in this application anyway? The mortar only really has to hold the brick in place.

The hydrate you have isn't much use for anything else and will soon wash out anyway but if you must then dry mix it 3:1 with coarse sharp sand.

I would still brush a dry mix (using fresh hydrate!) over the bedded bricks to grout them.

That's just time out of your life you'll never get back.
Traffic on the path and the elements will quickly wash away all your good intentions.

 

[Flyfisher]

Hydrate I would never use on a roof,you're asking for trouble.
You need to use hydraulic lime or a putty mortar with a pozzolan.

I used the mortar mix specified by the CO in the Listed Building Consent: 9:3:1, with the '1' being white cement. Could that be acting as the pozzolan?

I understand the point about stale hydrate resulting in a weaker mix but was wondering if this really mattered in some applications, such as bedding bricks in a footpath? A weak mix should, at least, allow the bricks to be easily reused (as I'm doing after, I guess, about 70 years).

It just seems a shame to send any 'past-it's-prime-but-still useable-for-something' hydrate to landfill.

 

[OddJob]

Your CO should know better,9:3:1 is a mix that was bandied about for years and it's now generally agreed it's wrong,no serious lime practicioner would use it or advise its use.
It's a cementicious mortar not a lime mortar,cement in itself is not strictly a pozzolan,a pozzolanic cement is lime with burnt material such as fly ash etc.
It's completely wrong and unnecessary to use cement anywhere on a lime structure.
Where needed lime mortars can be made just as hard and durable as cement mortars and still be breathable and able to cope with natural movement.

Yes,your hydrate is perfectly OK for bedding a footpath but not jointing it.
I'm getting worried here because people will start to think I think I'm the only one that's right :roll:
I'm not,there are many different ideas and opinions and many regional mortars and aggregates.
The mortars and plasters I use replicate most closely the original material found in my area.
When I did some work in Market Harborough many years ago the local sand was totally different and there are many variations down here.
There are several species of CO too,ignarus pretium still being quite common,like the dinosaur once was :wink:
As for yours I'm reminded of the old saying,
"Funny what you see when you ain't got a gun!"

 

[Flyfisher]

Just to clarify, the 9:3:1 mix was specified only for new work and not as a repair mortar. It was used to rebuild the top 1m of a chimney and for bedding the ridge tiles. Isn't that consistent with your earlier comments about not using hydrate on a roof?

 

[Schoolmarm]

FF, I think it is the combination of lime and OPC that is a big no-no.