Correct mix for lime mortar

[JohnD]

Just had the stone work on the old house and barn blasted to remove many years of old paint. She defiantly could do with a pointing job.

We need lime based mortar apparently anyone know the correct mix for this I seem to get conflicting views on what exactly lime mortar mix is.

 

[SilliamWhale]

Where are you based? If your a beginner to this you could buy it ready.mixed by the ton bag but haulage adds up from specialist lime people.

You could also mix up nhl 3.5 and sharp sand 4 to 1.

What you mean conflicting views?

 

[phillipe]

By by the bulk bag from brecon ,wouldnt use the rubbish myself,

 

[JohnD]

Thanks most people I have asked have recommended adding cement to the mix as well


From what I have read I gather this is not the done thing

 

[Land Rover]

I've used the pre bagged stuff I get locally .
Easy enough to work with and a choice of colours .
For a 25kg bag its about 17 quid .
There seems to be a big move towards using lime again , but every builder I speak to knows nothing about it .
I see a place in Lancashire https://www.heritage-store.co.uk/contact-us
Might be worth a look .

 

[multi power]

I don't think there should be any cement in lime mortar

 

[blackieman83]

@vikinglimey

 

[JohnD]

I've used the pre bagged stuff I get locally .
Easy enough to work with and a choice of colours .
For a 25kg bag its about 17 quid .
There seems to be a big move towards using lime again , but every builder I speak to knows nothing about it .
I see a place in Lancashire https://www.heritage-store.co.uk/contact-us
Might be worth a look .

Will give them a call only down the road from me to Thanks

 

[vikinglimey]

Just had the stone work on the old house and barn blasted to remove many years of old paint. She defiantly could do with a pointing job.

We need lime based mortar apparently anyone know the correct mix for this I seem to get conflicting views on what exactly lime mortar mix is.

No - there is no cement in lime mortar. Lime mortar is just limestone that has been burnt to produce calcium oxide and slaked (i.e. water added) to produce calcium hydroxide and then mixed with sand to produce the mortar. There are different grades of lime mortar based on its hydraulicity i.e. its ability to set through a chemical reaction rather than just in air. So NHL 2 is feebly hydraulic (generally used for internal plasterwork), NHL 3.5 is moderately hydraulic (generally used for internal and external work in average conditions) and NHL 5 Eminently Hydraulic (used for external work where bad weather or harsh conditions are common). NHL 5 is best for damp conditions.

You can colour the mortar using dyes to match your existing work. If made yourself you can use different sands to change the colour. You can make it yourself but takes a bit of practice. It did used to be made by farmers through the use of pit kilns dug into the fields as you only need to reach 900 degrees to burn the limestone and you can slake it with any water supply. Slaking is a bit of an art form as you can make a milk of lime up to a putty depending on the amount of water used. So old milking barns were coated with a very liquid mix (because lime mortar is also anti-bacterial) and in Scotland you see a thicker application thrown onto old buildings in the form of harling.

You do need a builder that knows how to use it though because it is handled differently to cement. It needs longer to set and needs a bit more skill to mix. You need to find those that are used to heritage restoration. There is a guy in Burnley knows his stuff and is probably the closest for you :

Philip Braithwaite UK Restoration Services Herd House Farm Halifax Road Briercliffe Burnley BB10 3QZ +44 (0) 1282 431155 +44 (0) 7818 410095 [email protected]

 

[Barleycorn]

Blimey the technical information you get on this forum is amazing!

 

[It was already broken.]

If it is a one off job I would buy ready mixed mortar in 25kg bags. I did some early in the summer as part of a larger job. Never used it before but worked a treat. Add water in the mixer and away you go. I went to a firm called Anglia Lime and that is all they do so knew what they were talking about, pretty sure they ship anywhere. Good thing about it is the mortar takes ages to go off which doesn't matter if you are pointing and if you get called away you don't come back to find it solid in the bucket.

 

[Philip Watkins]

Thanks most people I have asked have recommended adding cement to the mix as well


From what I have read I gather this is not the done thing

Have a word with this company http://www.treasureandson.co.uk/index.php it's what they do.

 

[suffolksmallholder]

I'd use moderate, NHL 3.5 at a ration of 3 parts sand : 1 part lime. You will need to 'wet' the wall first to make a key or else things dry too quickly & continue to wet occasionally after you have done the work. Over wetting will wash out the pointing. You are encouraging the crystallisation in the wetting process which is in effect the hardening. It takes three or more days for the process to start & this is what makes modern builders worried in that they don't believe the mortar will ever set!
You can also use lime putty for pointing. This sets in a different way so be careful. https://www.lime-mortars.co.uk/lime/non-hydraulic
NHL 3.5 is also good mixed as a slurry & applied with a brush onto your finished work to create a smooth finish & is as good as any paint. Again lime putty can also be used.
A hawk & gauging trowel or rounded nose pointing trowel plus an old metal bucket handle are the tools plus the wonderful Marshalltown joint raker to make the joints deep enough to hold the mortar & remove all the old carp.

You can dress the joints in any way you like & this theme should be carried on throughout the job or it will look like the cowboys have been in for a visit.
Red or yellow ochre were common dyes but there's a plethora in todays market.

Some more reading for interest;
https://www.lime-mortars.co.uk/articles/lime-hydraulic-or-non-hydraulic
SS

 

[jamesy]

Been doing a bit of pointing here this week- Roundtower NHL 3.5 white

 

[vikinglimey]

lovely job !!

 

[Ffermer Bach]

No - there is no cement in lime mortar. Lime mortar is just limestone that has been burnt to produce calcium oxide and slaked (i.e. water added) to produce calcium hydroxide and then mixed with sand to produce the mortar. There are different grades of lime mortar based on its hydraulicity i.e. its ability to set through a chemical reaction rather than just in air. So NHL 2 is feebly hydraulic (generally used for internal plasterwork), NHL 3.5 is moderately hydraulic (generally used for internal and external work in average conditions) and NHL 5 Eminently Hydraulic (used for external work where bad weather or harsh conditions are common). NHL 5 is best for damp conditions.

You can colour the mortar using dyes to match your existing work. If made yourself you can use different sands to change the colour. You can make it yourself but takes a bit of practice. It did used to be made by farmers through the use of pit kilns dug into the fields as you only need to reach 900 degrees to burn the limestone and you can slake it with any water supply. Slaking is a bit of an art form as you can make a milk of lime up to a putty depending on the amount of water used. So old milking barns were coated with a very liquid mix (because lime mortar is also anti-bacterial) and in Scotland you see a thicker application thrown onto old buildings in the form of harling.

You do need a builder that knows how to use it though because it is handled differently to cement. It needs longer to set and needs a bit more skill to mix. You need to find those that are used to heritage restoration. There is a guy in Burnley knows his stuff and is probably the closest for you :

Philip Braithwaite UK Restoration Services Herd House Farm Halifax Road Briercliffe Burnley BB10 3QZ +44 (0) 1282 431155 +44 (0) 7818 410095 [email protected]

Important to use "pit" sand and not dredged sand too, oh and maybe mix, then put in a barrow over night with plastic over the mix, then the next morning, back in the mixer again, to work it further

 

[milkloss]

Important to use "pit" sand and not dredged sand too, oh and maybe mix, then put in a barrow over night with plastic over the mix, then the next morning, back in the mixer again, to work it further

Why leave overnight?

 

[Ffermer Bach]

more for rendering, it makes the mix work better the next morning

 

[vikinglimey]

Why leave overnight?

Lime works better if time is taken in preparation, application and drying as you need to ensure it is fully slaked, mixed and cured to avoid failure - that is why modern builders don't like it.

You can actually store a pure lime putty for centuries as it will form a crust over the top that prevents it from hardening. It will stiffen up but will become pliable again with a good stiff mixing.

 

[Ffermer Bach]

when I worked in Denmark, we had lime putty in a pit in the yard, and would take some, and mix it with water for lime wash for the cattle sheds (years ago, cows were all tied up in stalls, now the farm is milking 250 cows in cubicles, but then there were 55 or so, and I moved the clusters down the shed to milk).