How come my lime mortar comes out gray/brown?

[robgil]

Its grey brown in colour and the old stuff is creamy white.

 

[johnandrew]

Hi Rob

I have a similar issue, Rob. The original mortar in one part of my house is very white and seems to be consists of hardly any sharp aggregate. I assume this is a very rich lime mix and that's why it is so white. The test mixes I have tried so far have come out a very light grey colour but using a sharp sand aggregate they are much more gritty than the original and not as white.

Also, what lime are you using? I've heard the French hydraulic limes do come out quite grey and maybe the brown is due to the fine particles in your aggregate.

John

 

[Louis Henry]

I've found it's always the colour of the sand that matters. I'm scratching my head at the moment because I'm doing some repointing but the last couple of bags I bought are reddish rather than yellow. I'm going to do some test mixes with all yellow, all red or a mixture and see what they look like in a small patch. Of course what I should have done was got enough sand for the whole house, but I'm a slow worker!

 

[middi]

Two parts soft sand ( not the washed type), one part sharp sand and one part hydrated lime.

It will be just what you are looking for, white,simple, effective and cheap.

Middi

 

[rebeccac]

Could there be some chalk in the ol mortar?

 

[robgil]

Could be chalk in there , I wouldn't be surprised. would putty do instead of hydrate? I don't know anywhere local that sells hydrate , its all NHL round these parts.

 

[MdB]

Could be chalk in there , I wouldn't be surprised. would putty do instead of hydrate? I don't know anywhere local that sells hydrate , its all NHL round these parts.

Jewsons do as probably other builders merchants. It is commonly used in 6:1:1 mixes and our local branch goes through something like 1 pallet of lime for every 10 of cement. NHL on the other hand is difficult to get hold of here.

 

[robgil]

jewsons want something like 40 quid for a tub of putty here.

 

[Flyfisher]

I can second MdB's comment. Rob, I get all my hydrate at Jewsons in Watton, not exactly local to you I know, though not too far if you're really stuck. But I'd be surprised if you can't find a more local source. I'm paying about £8 per 25kg bag.

 

[robgil]

I will have to have a shop around, there are more building suppliers around here than there are building sites so I'm sure someone will have some.

 

[MatthewC]

Two parts soft sand ( not the washed type), one part sharp sand and one part hydrated lime.

It is commonly used in 6:1:1 mixes and our local branch goes through something like 1 pallet of lime for every 10 of cement. NHL on the other hand is difficult to get hold of here.

I know that Middi and FF know a lot more about it than me, so could you please educate me about hydrated lime? I have found on-line (OK, I know that there's a lot of duff gen out there) that hydrated lime is not breathable, and that in a 6:1:1 mix (cement & hydrated lime) the only purpose of the hydrated lime was to improve the elasticity of the mix. Please, is it or is it not OK to use it for (e.g.) pointing where the original was lime-putty based?

I shall be getting to that stage later in the year, and I'm confused.

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[MdB]

Cement Mortar - non breathable
Typically around 4:1 sand:cement

Cement Mortar with lime added for added plasticity/workability - non breathable
Typically 6:1:1 sand:cement:lime
(mixes with more lime than cement shouldn't be used as the cement tends to clump making in worse than no cement at all)

Lime Mortar (hydrate) - breathable - won't set whilst wet
Typically 2:1 sand:hydrate (more lime may be better)

Lime Mortar (putty) - breathable - won't set whilst wet
Typically 3:1 sandutty (more lime may be better)

Lime Mortar (NHL) - breathable - will set whilst wet
Typically 2:1 or 3:1 sand:NHL (more lime may be better)


Limestone + heat makes Quick Lime
Quick Lime + just the right amount of water makes Lime Hydrate (a dry powder) + Heat (Dangerous)
Quick Lime + lots of water makes Lime Putty + Heat (Dangerous)
Lime Hydrate + water makes Lime Putty (not dangerous)
Lime Putty + water makes Lime wash

Buy Lime Hydrate from normal builders merchants (keeps 3 months to a year according to manufacturers unopened).
Buy Lime Putty from specialist Lime merchants (keeps forever if kept damp) or make your own from hydrate.
Buy NHL (Naturally Hydraulic Lime) from Lime merchants (keeps for 3 months to a year I think unopened).
Don't buy Quick Lime....

I think I've got that right. Corrections please.

 

[Flyfisher]

That looks about right to me.

Frankly, I don't really understand the difference between lime putty and hydrated lime - apart, perhaps, from some 'workability' issues. As I understand it, chemically the two are the same thing, as is the end result. Both will produce a breathable mortar.

I tend to simply think of hydrate as a dry version of putty and putty as a wet version of hydrate. After all, it's well known that putty can be made up from hydrate by simply adding sufficient water, which is a convenient way of storing lime for a longer period than the powdered hydrate.

I suspect the breathability confusion arises because, as MatthewC rightly says, lime is often used to increase the plasticity of cement mortars to make it more 'workable'. The end result is a non-breathable mortar because of the cement in the mixture, not because the lime is non-breathable. And in the right application, of course, there is nothing wrong with such a non-breathable mortar mix. But where breathability is important then it's the cement that has to go.


I sometimes wonder if putty is often revered over hydrate because historically the result of slaking quicklime with water would naturally be a putty as the process was not able to be controlled finely enough to product hydrated lime, as can be done today. Thus, quicklime would be locally slaked in a simple pit and might have been left for months during a construction project. Nowadays, such a process is would not be deemed acceptable practice but fortunately we now have the capability of slaking quicklime to such a precise degree that the end result is an easily-bagged, stored and transported solid hydrated lime product. Just add water when needed and, hey presto, lime putty!

I suspect we tend to over-obsess about mix ratios and constituent purity these days (I know I do!) whereas many (most?) historical mortars would have been made up from roughly shovelled portions of lime putty from a hole-in-the-ground together with sand from a nearby riverbed or perhaps just a very sandy soil - impurities and all.

 

[MatthewC]

Thanks, FF and MdB, that's really helpful

Frankly, I don't really understand the difference between lime putty and hydrated lime

I'm glad I'm not alone!

I suspect the breathability confusion arises because, as MatthewC rightly says, lime is often used to increase the plasticity of cement mortars to make it more 'workable'.

I'm glad I got something right!

Just add water when needed and, hey presto, lime putty!

I didn't realise that

many (most?) historical mortars would have been made up from roughly shovelled portions of lime putty from a hole-in-the-ground together with sand from a nearby riverbed or perhaps just a very sandy soil - impurities and all.

As, I suspect, the mortar on my house was. It seems to have used a very fine sand which now crumbles where it has been subject to prolonged damp, hence the need for some re-pointing

One last question: if we use 6:1:1 for my new extension, can that produce a finish which is comparable to the lime on the existing house (so long as we can match the colour, which was the original question on this thread!), or does it give the hard-looking cement finish?

Matthew
http://houseintheenchantedforest.blogspot.com/

 

[worms]

many (most?) historical mortars would have been made up from roughly shovelled portions of lime putty from a hole-in-the-ground - impurities and all.

Not forgetting the cinders and ash from the fire that burnt the limestone in the first place!

 

[johnandrew]

many (most?) historical mortars would have been made up from roughly shovelled portions of lime putty from a hole-in-the-ground - impurities and all.

Or from fresh quicklime, water and sand to make a hot lime mortar as mentioned in Gerard Lynch's article referenced in another post. I'd like to try this, or at least see it done.

MathewC, I think you are right about role of lime hydrate in a 6:1:1 mix. It's used as a plasticizer.

On the difference between putty and hydrate, my book on hydraulic lime mortars, says

Prolonged storage of lime putty allows it to dissolve and re-crystallise repeatedly, which results in much finer than normal crystal sizes that enhance its plasticizing ability. In other respects it acts as dry calcium lime [hydrate].....

 

[MdB]

One last question: if we use 6:1:1 for my new extension, can that produce a finish which is comparable to the lime on the existing house (so long as we can match the colour, which was the original question on this thread!), or does it give the hard-looking cement finish?

I think you will find that 3:1 Sand:Cement and 6:1:1 Sand:Cement:Lime will look the same apart from the colour with the 6:1:1 looking a bit lighter but not by much - Not too sure though. You may want to look into using white cement as a possible match.

 

[middi]

A 6:1:1 mix ( using white cement) is very good to build with. Especially good to match old lime wall joints when a 3:3:1:1 mix is used ( the 3 being equal sharp and soft).

For pointing old walls the 8:2:1 mix can be used ( the 2 being hyd.lime and 8 a mix of sharp and soft sand), this is an excellent match and gives good result when used on very soft bricks.

Using white cement is only a matter for the conscience of the conservationists.
It does a very good job and sppeeds things along for those that are willing to compromise. Used in mixes as above, the breatheability factor is dimished somewhat compared to a pure lime mix. The 8:2:1 mix has a very good pourosity factor and bricks will not be harmed by frosts.
The combinations are endless. A lot depends on individual preferences, directives from a conservation viewpoint and most of all experience in apllication of these mixes under those conditions for which they are best suitable.
Middi

 

[robgil]

I used the old mortar crushed with my lump hammer and added some putty , seems to have worked.

 

[Zebra]

Help!!
I've been using a mix of two parts soft sand, one part sharp sand and one part hydrated lime to point most of my house. However, I've just been told though that I'm using the wrong type of lime!
I'm using Lafarge's "Hydralime" which claims to be a high calcium, non hydraulic, hydrated lime but it is intended as a plasticiser for cement mixes, and it does say on its product literature that as its not a hydraulic lime it should not be used without cement. I've been ignoring this thinking it must be the right stuff. I thought it was similar in consistency to the ready mixed stuff from the Old House Store that I was using before. But its not setting very hard, it's setting kind of crumbly, and it's yellow not white, and a listed building expert who came to advise me on other things said I should be using 3 parts sharp sand to one part Hydraulic lime, and working it a lot before putting it in. Is there a different type of hydrated lime that I need to use? Or do I need hydraulic? Do I need to start all over again?!!
Appreciate any advice!!
Z