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GSBN:Recap on what I learned on lime
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- Subject: GSBN:Recap on what I learned on lime
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- Date: Tue, 14 Dec 2004 10:33:34 +0100
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In Europe we distinct 2 types of (natural) lime:
(In Eupope 'non natural' limes are basicly low strength cement)
1. Calcic Lime - CL
Burned limestone with <4% silicium-clay content. Fired at 800-900¡ C
(It seems that 100% pure limestone does not exist in nature).
This lime (called 'A?rienne' in France which means 'air') carbonates when in
contact with the air and therefore needs to be applied in layers of up to 1 or
1.5 cm (very few sources allow 2 cm). A trick of the trade seems to be to add
beer (=CO2) to the mix if on is obliged to go more thicly. How this affects
quality I cannot say, and I have allways preferred to pour it down my mouth.
This type of lime has a very slow curing process. But this is the type of lime
that breaths most. Low strength, but flexible (few cracks, moves somewhat with
2. Natural Hydraulic Lime ö NHL Fired arround 1100¡ C
> 4% < 20% silicium-clay content
'Hydraulic' because it reacts with water, and is in no need for contact with the
air. Basicly used for foundations (even those of bridges etc). Its reaction is
faster than that of Calcic Lime, it is stronger and less air passes through it.
Usually not advised for plastering, unless for fa?ades that receive excessive
amounts of rain.
This (hydraulic) difference is very important as it was discovered by a
Frenchman (Louis Vicat) in 1913 ;-)
4-8% silicium-clay content NHL 2
8-14% silicium-clay content NHL 3.5
14-19% silicium-clay content NHL 5
* Lime allways has to be extinquished by adding water to the lime. In the case
of Calcic Lime (CL) this can be done on site and left to slake. For this
purpose it needs to be under water in order to avoid contact with the air.
* Lime should not be allowed to dry before curing (which is a reaction, not a
drying process) is well set in as drying disturbs the curing procces. This is
most delicate for CL as it has a longer drying p?riod. Soak the support well
the day before and several hours before plastering. If needed mist again just
before plastering, but take care not to add too much water. Avoid direct sun,
too much wind and freezing.
* Lime can crack when to high a dose of lime or clay is used or when thickness
* Non throweled lime plaster can soak up water and let it pass trhough.
Throweling closes the poores. A smooth surface makes the water run down.
Then there is cement, Fired arround 1300-1400¡C
More or less the same stuff as hydraulic lime, but fired at slightly higher
temperatures and an even higer silicium-clay content. >20%
It reacts in contact with water, it reacts even faster than NHL and is stronger.
It lets less air pass through than NHL.
Also, it is not extinquished as is lime, but rather it is milled to make it into
To finish it off:
Hydraulic lime that contains (no more than 20%) cement
Hydraulic lime that is not natural. (basicly blends)
Clay and lime.
In the old days, lime was mixed with earth, basicly a type of earth that would
work well as an earthen plaster or (more commonly) a type of earth that
contains too litte clay to make it work as a plaster. The clay gives colour to
the otherwise white (CL) or grey (NHL) lime plaster. When an earth contained to
much clay sand was added.
But: The clay also has a chemical reaction with the lime or vice versa (?)
Anyway, the lime destroys the binding properties of the clay. This is why a
eathen plaster does not get stronger just by adding a bit of lime. Enough lime
needs to be added so that lime wins the struggle.
How to determine how much lime to use (on clean or unwashed sand):
Take 2 buckets and fill them both to the same level.
One with the sand, on with water.
Pour the water on the sand until the water reaches the level of the sand
Wait 1 hour, add water if it has 'sunken'
Calculate how much water was added to the sand, relative to volume of sand.
1st layer (like a thick soup) 5 vol. Lime for 10 Sand
2nd layer 4 lime ö 10 sand
3rd layer 3 lime ö 10 sand
This is supposed to avoid having cracks one over the other
Pascal Th?paut (who works as a proffesional SB builder in France) uses:
1 lime (straight out of the bag) for 3 sand
First layer : 50% Hydraulic lime (NHL) 50 % Calcic lime (CL)
Second and third layer only Calcic lime (CL)
The hydraulic lime makes the plaster set more quicly so the second layer can be
Lime is wonderful, Earth is a miracle !
Selon Chris Magwood TLSEditor@...:
> I was always under the impression that lime was built up in thinner
> layers because of the need for the lime plaster to recombine with
> atmospheric CO2. If it goes on too thickly, not only will it crack
> because of it's own weight sliding down the wall before it sets, but
> it won't cure fully because the stuff that's buried deep won't
> carbonize properly. But somebody with more lime knowledge might be
> able to shed more light on this subject!
> I think what the testing at Queen's suggests is that regardless of
> the kind of plaster or its final compressive strength, the thicker it
> goes on, the stronger the final wall assembly. This is not surprising
> in itself, but what surprised me was that the thickness made so much
> more difference than the plaster strength. Better to have 30mm of
> quite weak plaster than 10mm of super strong stuff. I think it helps
> make the case for earthen plasters, which like to be thick and don't
> cost a lot to make thick, and who cares if they're not quite as
> strong as a cement-based plaster.
> >for lime one layer should not exceed more than 10 mm due to moisture
> >protection, so building up thickness traditionally is done in layers
> >(normally 3). Does this team is confirming this tradition?
> Chris Magwood / Camel's Back Straw Bale Construction
> <a target="_blank" href="http://www.strawhomes.ca">http://www.strawhomes.ca</a>
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