Hydrated Lime Question

[Flyfisher]

In a previous thread there was some discussion about failure mechanisms when using lime hydrate in mortar mixes. I mentioned that I'd had some lime mortar fail over winter, even though the work had been done in the summer so it definitely wasn't a frost-while-setting problems. It was also alongside similar lime mortar that didn't fail.

Two possibilitie were offered:

1. The original work was not covered and kept damp, so the mortar could have dried too quickly thus hindering proper carbonation as this is facilitated by C02 dissolved in water

2. The lime hydrate might have gone 'stale', i.e. already partially carbonated through exposure to air, which is why lime putty is more desirable as it keeps indefinitely.

Thinking about this while re-laying a path yesterday confused me somewhat (my fault for thinking!). If lime mortar requires to be kept damp in order to thoroughly carbonate to full strength, i.e. the water facilitates setting, why can putty be kept indefinitely under water?

 

[biffvernon]

That's easy. The 'setting' Is the reaction of carbon dioxide in the atmosphere with the calcium oxide in the lime to form calcium carbonate. Under water not much CO2 reaches the CO so the lime is protected. In dry air the CO2 can get to the CO but the reaction is very slow. In damp conditions, the CO2 dissolves in the water and then reacts with the CO2. This is a much faster reaction.

 

[Penners]

Great answer. I'm learning - but oh, so slowly....

 

[robgil]

so does this mean that lime mortar will go off quicker if kept in damp conditions?

 

[Schoolmarm]

Don't forget Rob you have "drying out" and "going off" it needs to go off, as in set properly and slowly, by carbonating and not dry out too quickly before this happens.


If you mean go off as in spoil during storage, you need to exclude as much air as possible and keep moist.

 

[Flyfisher]

That's easy. The 'setting' Is the reaction of carbon dioxide in the atmosphere with the calcium oxide in the lime to form calcium carbonate. Under water not much CO2 reaches the CO so the lime is protected. In dry air the CO2 can get to the CO but the reaction is very slow. In damp conditions, the CO2 dissolves in the water and then reacts with the CO2. This is a much faster reaction.

Yep, that was my understanding, but isn't there an inherent contradiction?

"Underwater not much CO2 reaches the lime so no reaction". Fine - lime putty lasts for ages if underwater.

"In dry air the CO2 can get to the CO but the reaction is very slow." Fine - so hydrated lime should remain OK for a reasonable period of time (can this be quantified?).

"In damp conditions, the CO2 dissolves in the water and then reacts with the CO. This is a much faster reaction" Fine, which helps explain the importance of keeping new lime work damp to aid setting . . . . except that since CO2 dissolves in water and reacts quickly with lime, why isn't lime putty similarly affected?

I may not be seeing the wood for the trees!

 

[robgil]

so the lime step that ive just poured may need to have a wet blanket put over it to aid it in going off?

 

[OddJob]

There is no contradiction and if I remember correctly it was explained in the thread.
All new exterior lime work should be covered in damp hessian,especially in hot weather,in wet weather you can cover the hessian with a tarp and leave the hessian dry.
The damp hessian allows airflow while at the same time retarding the drying out and set,if the mortar dries too quickly it won't cure,if weather conditions are too wet the same applies,lime mortar should carbonize slowly but not too slowly,too quickly and it turns to powder.
Lime mortar will not "go off" quicker in damp conditions,it will cure slowly,as it should.
Even in a sealed bag hydrate will take in moisture from the air,no air can get at sealed lime putty.
I seem to remember your mortar was a cementicious hybrid.

 

[OddJob]

so the lime step that ive just poured may need to have a wet blanket put over it to aid it in going off?

No,to stop it going off too quickly.
Don't tempt me with the wet blanket question.....I have someone in mind :lol:

 

[Flyfisher]

I guess I wasn't fully understanding the role of water in the carbonation of lime. On the one hand it seems to be essential for facilitating correct carbonation of mortar yet on the other it protects lime putty from the same carbonation.

As I previously hinted, it all seems to be a matter of time and is as much about physics as chemistry; putty WILL eventually carbonate, but it happens far slower than in damp mortar, essentially because of the much lower effective surface area for CO2 and water to react to form carbonic acid, an essential step in the carbonation process.
http://resources.metapress.com/pdf-preview.axd?code=wg72727tknl181k9&size=largest (among many others).

Even in a sealed bag hydrate will take in moisture from the air

Even a sealed plastic bag?

I seem to remember your mortar was a cementicious hybrid.

That was specifically for a chimney rebuild (that has no signs of failure even through the recent hard winter) - this is a more general question.

 

[middi]

Talking from experience. ( I will leave you all to sort out the science aspect)

Hydrated lime mortars WILL set much better if the ambient temp. is not too hot or cold and with high atmospheric humidity, it could take up to five weeks( or even longer !!) if conditions are very damp. The biggest problem, if conditions are very damp, is the risk of unexpected frosts before all the water has had the chance to evaporate during the curing process and depending on how hard the frost or at what stage the curing process has progessed the degree of damage is pro-rata with these conditions.

As to hydrated lime mortars in hot weathers the only problem to this is the very fast evaporation of water from the mortars which leads to heavy shrinkage and cracking therefore not a uniform bonding but it will still set quite hard

 

[OddJob]

Jesus H feckin' Christ Flyfisher!
Whatever it is you're on mate you need to get down the docs and get that prescription changed :evil:
To quote you from the previous thread,

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.

So it wasn't just for the chimney was it,or did you just use hydrate on the roof?
If so you answered your own questions,and asking the same questions again from the previous thread,why?
You admitted you had a failure.

In a previous thread there was some discussion about failure mechanisms when using lime hydrate in mortar mixes. I mentioned that I'd had some lime mortar fail over winter, even though the work had been done in the summer so it definitely wasn't a frost-while-setting problems. It was also alongside similar lime mortar that didn't fail.

For the life of me I don't understand your increasingly anal obsession with hydrated lime :?

Even a sealed plastic bag?

Yes!
As has been explained hydrate comes into contact with the air as soon as it's produced,putty from quicklime doesn't,I would have thought that was blindingly obvious,hydrate draws moisture from the air.
Hydrate has an alleged shelf life of 3 months(IMHO much less)putty is even better when matured for at least 6 months before you even think about using it,do the math.
Even the tiniest bit of moisture in the air will begin the completion of the lime cycle.
You could vacuum pack it and send to the bloody moon,it would still be a bag of shite!

I fail to see why you're making such big thing about it,it's not rocket science,if you're so desperate to go into chemical formulae etc then RTFM!
http://www.amazon.co.uk/Building-Lime-Introduction-Stafford-Holmes/dp/1853395471
Stop fretting about it and buy the bloody book for Heavens sake,if you don't want to do that order it from the flipping library for free!
Sometime I wonder if you're deliberately trying to wind me up :roll:

Oi Gervase,what was the number of that bus you took out of here and can I get a ticket for the next one!

 

[robgil]

bugger , ive had an open bag of nhl 3.5 sat in my kitchen all winter that ive been using every now and then , do you reckon its past its best then? its still powdery?

 

[robgil]

bugger isnt a bad word is it?

maybe it was at one time. :shock: http://en.wikipedia.org/wiki/Bugger

 

[Flyfisher]

Calm down Oddjob or you'll be the one needing a prescription. :lol:

The reason I started a new thread was precisely to discuss the mechanisms involved rather than any specific building application.

I wanted to better understand how water helps carbonation in mortar but prevents it in putty. If that's an obsession, so be it.

Hydrate has an alleged shelf life of 3 months(IMHO much less)

Thank you. I think that's the first quantitative answer we've had on this topic. Even then there seems plenty of room for doubt.

I fail to see why you're making such big thing about it,it's not rocket science,

It may not be rocket science but you might be surprised at all the differing views and advice that crops up whenever the use of lime is discussed. My approach tends to be to try to fully understand a subject; I like to understand the 'why' as well as just the 'what'.

I'm sorry if questions wind you up. I won't be offended if you don't answer them.

 

[OddJob]

[Bad Word] isnt a bad word is it?

maybe it was at one time. :shock: http://en.wikipedia.org/wiki/[Bad Word]

Dunno,what was the bad word....I know most of them :lol:

ive had an open bag of nhl 3.5 sat in my kitchen all winter that ive been using every now and then , do you reckon its past its best then? its still powdery?

Yes,but someone will say different,someone will say "Well I've used old lime and had no problems so he's talking out of his [Bad Word]"
:lol:
It will have taken in moisture,you might find it seems fine on top but deeper down there's great big lumps.
Simple test,sieve it,you'll find lumps

 

[biffvernon]

"In damp conditions, the CO2 dissolves in the water and then reacts with the CO. This is a much faster reaction" Fine, which helps explain the importance of keeping new lime work damp to aid setting . . . . except that since CO2 dissolves in water and reacts quickly with lime, why isn't lime putty similarly affected?

Well it does get a bit complicated. A thick layer of water insulates the lime from the CO2 in the air as only a little dissolves in it. A thin layer - the microscopically thin film of dampness - allows atmospheric air to get at the lime with the bonus that the reaction goes quicker in water.

 

[robgil]

bugger , its not a bad word though , look http://dictionary.reference.com/browse/bugger , see?

if i were to use the sieve on a bag of lime ms robgil would leave me.
il give it a whirl.

 

[Flyfisher]

Well it does get a bit complicated.

Yes, I now understand that there's physics involved as well as the basic chemistry. Perhaps I am a bit obsessive. Still, it helps to keep the grey matter ticking over. :wink:

 

[OddJob]

It may not be rocket science but you might be surprised at all the differing views and advice that crops up whenever the use of lime is discussed. My approach tends to be to try to fully understand a subject; I like to understand the 'why' as well as just the 'what'.

Not at all surprised,just surprised that advice has been given by others and you still ask the same tired old questions when you already know the answers.

Thank you. I think that's the first quantitative answer we've had on this topic. Even then there seems plenty of room for doubt.

No it isn't,the answer was given in the old thread by someone else,as for the doubt well that's in your mind not mine.
In approx the past 16 working days I've got through 15 bags of NHL and 7 bags of hydrate.
How many did you get through?
Multiply that by 15 years of working with building limes in all their forms and I think you'll understand why I have no doubt.

I have no problem with your questions,I just wish they were asked by someone else who genuinely needs help with lime,not someone who needs more comprehensive help from the medical profession.
I have a question,how did you slip the laptop past Matron?