Hydrated or naturally Hydraulic Limes?

[Anonymous]

hi there

I am confused over the difference between St Astier naturally-hydraulic lime and hydrated lime from a builders merchants.

Hydrated seems to go off harder but still appears to be porous when hard (and therefore presumably breathable to some extent?)

I have read conflicting information which includes the suggestion that Hydraulic limes can also be hydrated but I have a feeling that the hydrated lime from a builders merchants is less breathable than St Astier.

I have also read that hydrated limes are very good for waterproof external renders which sounds like they are not suitable for a period property.

Which is more appropriate for a period property?

Any thoughts anyone <IMG SRC="http://www.periodproperty.co.uk/discussing/smileys/smile.gif" BORDER=0 ALT="">

Thanks, Rob

 

[Anonymous]

Hydrated lime, the dry powder in the paper sack at the builders’ merchant, is limestone that has been heated to turn it into quicklime, and then slaked with just enough but no more water to turn it into hydrated lime. When mixed with more water and sand it makes lime mortar/plaster. It sets slowly by absorbing carbon dioxide from the air, which turns the hydrated lime back into limestone. It will not set under water but remains as lime putty.

Lime putty bought wet in plastic tubs has been slaked with an excess of water so misses out the dry powder stage. It is better in some circumstances but chemically very similar. It is available through several specialist suppliers but not from many general builders' merchants.

Hydraulic lime is also bought as a dry powder. It is mostly hydrated lime but has a small proportion of ‘pozzolanic’ material. This makes it set when wetted, rather like Ordinary Portland cement. It makes a mortar that is a little stronger, more waterproof and less breathable than the basic hydrated lime and will set in wet situations. It is used in situations where these properties are desirable – foundations, harbour walls, river bridges, chimneys etc. In most situations it is better to use hydrated not hydraulic.

Naturally hydraulic lime has the pozzolanic material in the limestone from the start without being added. Most of what is available in England comes from France such as from St Astier. It comes in various grades of hydraulicity.

Hydrated is fine for external render. Rain soaks in somewhat and then dries out when it stops raining. Usually it is not raining (even in Manchester).

 

[Anonymous]

There are those who think mature, non-hydraulic putty is superior to hydrate for historic buildings.

It's worth reading up on it.

SPAB has a number of publications availble on the topic.



http://www.spab.org.uk

 

[Anonymous]

Hello,

I am currently trying to sort out a spec. for rendering the rear elevation of an 1895 terrace. The construction is 9 inch thick brick walls, and the building was originally rendered.

I am considering the relative merits of Hydrated Vs hydralic lime, the latter being somewhat cheaper.

Biff, you state that hydraulic is stronger, and less permeable than Hydrated. I am trying to get an idea of how much benefit from breathability would be afforded by using NHL3.5 (Blue lias) as compared to Hydrated lime.

Lets say on a scale of breathability, Hydrated is 10 and cement render is 1, could you suggest where NHL 3.5 would sit.

Thanks
D.T.

 

[Anonymous]

Somwhere between NHL 2 and NHL 5, (he says unhelpfully). I think you need to talk to one of the specialists:

http://www.traditionallime.com/
http://www.lime.org.uk/
http://www.womersleys.co.uk/
http://www.mikewye.co.uk/

etc.etc.

 

[Anonymous]

Only a good shaped pure hydratic lime plaster will work well to use at a historic period property. There are many technical reasons, here are some of them:

1st The thermal expanding of lime mortar and stone are very even (0,5-0,8 mm/m/100K), cement mortars (and hydraulic lime mortar is one of them) will expand much more (~ 1,2) than the stone. Result: Cracks of the mortar, mostly seen outside, where is more thermal difference.

2nd The drying out capacity (after Cadlergues) of lime mortar is 0,25, cement (and hydraulic lime) mortar about 2,5. Result: The hydrated lime mortar will dry out damp ten times quicker than hydraulic mortar. No storeing of water, much frost attack will be avoided.

3rd The binding forces by drying out of the fresh mortar is low of pure hydratic lime mortar and very high of cementous mortars. Result: No problems of binding from lime mortar on a 'weak' surface like an old wall, jointed normally with lime mortar.

4th The cement mortars and the hydraulic lime have a lot of efflorescent alkalic salt deposits in it, which can make many problems. Only pure hydratic (not hydraulic!) lime mortar has no efflorescent salts in the receipt.

5th Its not a problem by receipting lime mortar by use of 'shovel method' 1 part lime - 3 parts sand. I do prefer traditional methods in this topic. They are proved for centuries.

6th The pore volume and sice can influence the capillary and drying out behaviour of mortars very much. So the walls behind hydraulic mortars will be more damp than behind pure hydratic lime mortar.

7th The first layer of mortar should be grained 0 - ~4 mm, the finishing 0-~1 or 2 mm, depending of the original mortars nearby. So you can install a capillar pump, which will hinder water to came in and improves water to come out. Remember: Capillary transports are working only from big pores to small pores, so the fine grained mortar gets small pores, the rough grained bigger ones.

8th The salty aluminate deposits in hydraulic substance in the mortar can react with sulfates in your wall and create swelling salts, which can tear off your render.

If you will know more details to this topic and can understand german, try this:
http://www.konrad-fischer-info.de/29bausto.htm - Masonry - a technical Guide

In english you will find info about mortar problems on the link.

The problem is, that 'modern' craftsman are not more used to work with pure hydratic lime mortars, so they will recommend other things without respect of technical behaviour. Look for an old fashioned craftsman, there are many also in the UK. Perhaps ask the National Trust or Historic lime center or my fellow Peter Cameron from Historic Scotland at Fort George, there they know the good guys (and give them my greetings).

Good luck!

Konrad

My Tip: Never use Portland Cement and hydraulic substance in mortars, they will hurt masonry!



Lime mortars+others - my RILEM-lecture

 

[Anonymous]

This would be very useful if I could understand it. I dont even know what hydratic lime means. Does anyone understand this better?

NT

 

[Anonymous]

Non-hydraulic possibly?

 

[Anonymous]

I can not imagine that there would be a better introduction than Biff posted on 10.12.05 in this thread.

Shortly said:

Hydratetd lime hardens only by 1st adhesion and 2nd later carbonating with CO2 from the air to limestone.

Hydraulic lime can harden under water, building up cementitious minerals like Calcium-Silicate-Hydrates, but also swelling salts like Ettringite. It will be much harder than hydraulic lime and therefore will get more cracks. The pore system in hydraulic lime is smaller and more dense, so it can store water much more longer time as hydratet lime mortar.

High intelligent conservators and craftsman are not trusting the pure hydratic lime (because lack of knowledge and experience), so they use hydraulic cementitious substances as binder in lime mortars.

So hydraulic lime is an other word for cementitious mortar binder, but it sounds as 'lime', what seems to be a favourable thing for them and they can proudly shout: 'We are lime experts!'

For me its a fake to make lime mortars with added hydraulic binders, because the results are awful.

More details on the link.

Best regards

Konrad



Lime Mortar - A Mystery?

 

[Anonymous]

I'd recommend that anyone still mystified reads Jane Schofield's little book on lime - available from SPAB for less than a fiver. Other lime info and leaflets available there too.

Hydraulic lime is not the same as Portland cement, and it does have its place in some building work - under water, for example. Feebly hydraulic is recommended for chimneys even by SPAB. It is useful under water.

Bagged hydrate mixed with water and left to form a putty is what some people use, but it's not the first choice of many.

Mature, non-hydraulic lime putty is usually regarded as the best stuff to use. There are some differences of opinion about this however.

SPAB has a free technical quieries helpline - you don't have to be a member to use it.

Unless there is historic precedent, Portland Cement is NOT recommended for old buildings.



http://www.spab.org.uk

 

[Anonymous]

hydrated non hydraulic wins every time.

 

[Anonymous]

You talking about the stuff in bags from builder's merchants? Mixed up then left a day or two to form a putty?

I know that some disagree that it's as good as mature pit lime... but I'm not enough of a chemist to be able to argue.

Certainly Peter Maitland Hood thought it not what he would use or recommend. Did discuss this with him.

All better than Portland cement of course!

 

[Anonymous]

I agree totally. And there is very few difference and often none between a mortars structure and behaviour done with portland or hydraulic lime (where it is common to mix in undeclaratated portland or white cement).

For me it seems a little bit funny to bring other things than french wine and cheese over the Channel. Is there no production of dry hydrated lime in the UK? I would prefer this, its cheapest and works well.

Ok, maybe the english weather needs more efforts for under water building than here in Germany ;-)

Best regards

Konrad


Building repair over sea level in Germany

 

[Anonymous]

yes; plain and simple dry hydrate from j***sons etc etc.

aside from price, the only difference between dry hydrate and putty is the amounnt of water added to the quicklime in the production process - less for hydrate, more for putty - and the argument that it 'goes off in the bag' is no longer applicable as most companies do it in a plastic line, as per opc. i could go on about the pro's and con's of either with regard to historic mortar comparisons..... but.... just remember that a non hydraulic hydrate is perfectly fine. as for hydraulic lime.... fine for a chemical set.... or in place of opc... but that, i.m.h.o, is about it.

 

[Anonymous]

c*stle cemt - who produce non hydraulic hydrated lime - have works in this country......

 

[Anonymous]

Portland has its place though Konrad!


http://www.concretecastle.com

 

[Anonymous]

What a load of misinformation, where to start?

Castle Cement do not own any Lime Kilns in this country. There hydraulic lime is bought in from Socli in France, non-hydraulic from Buxton.

If you are buying Natural Hydraulic Lime, & it contains portland cement as Konrad suggest, the manufactureer is breaking the law, sue them. They may only brand it as 'HL' if it does contain PC, not 'NHL' (a confusing difference, admitedly). Would you care to name the manufacturers who are doing this, or provide some evidence?

There is a massive difference in structure between Portland & hydraulic lime mortars. Read 'Foresight' if you don't believe this - you can see it in the data & the microscope pictures.

In response to the original question - it would be a lot easier if people didn't mix & match descriptions. Either describe the type of set (hydraulic vs. non-hydraulic, or CL90 vs NHL2, 3.5 or 5) or the physical form (putty, quiklime, hydrate).

Non-hydraulic is fine if used correctly (a bit like mostthings, really), but don't fall for the myth that its 'traditional'. They didn't have ye olde worlde gas fired kilns, & limestone in derbyshire is unusually pure (which is why the kilns survived there, supplying the Steel industry which wants only pure limes).

 

[Anonymous]

whether or not c*stle have lime kilns in this country was not the original question!

 

[Anonymous]

No, it wasn't the original question & is minor, but would it be less incorrect if it was the original question? My point is, that this site could be incredibly useful, but there is so much incorrect information posted about what I do know, it puts a doubt in my mind about everything else I read.

 

[Anonymous]

ok; not a direct question, a response to a comment.

anyway.

reading the site is akin to reading any other information. the printed (and published) word cannot always be taken literally - lots of misinformation in other sources also. read, dismiss, adopt and advocate what you belive in.

this is a discussion forum not a reference library.