Repointing using lime mortar

[pgrbff]

look at masons mortar. they're honest and can provide an abundance of information. I have been using them since the 90's.
in the last 3 years, I have spent probably 15K on materials alone for plastering.
It isn't difficult to mix but you need not just the correct colour sand but the correct grade, ie the correct mix of sizes of particles.
Here in Italy, even builders don't mix their own, it comes in bags with sand included and you just throw it in the mixer.
Don't add too much water, it tends to get fattier the more you mix it.

 

[MikeJhn]

The bags of lime mortar are the easiest way to get consistent colour, as above, in France its only the Brits who source the sand and lime separately and mix it themselves. Available in various colours from tan too grey, in most of the shed type DIY stores, I'm sure it must be available in the UK as well.

I minute search: DRY BAGGED LIME MORTARS – “MIX & GO” – masons mortar

 

[Sandyn]

look at masons mortar. they're honest and can provide an abundance of information. I have been using them since the 90's.

A big thanks!! I just did. They are local to me, prices look very very good and they have a fantastic range of products. I would just go for the premixed. I can take a sample stone along and match the colour

 

[Sandyn]

I minute search: DRY BAGGED LIME MORTARS – “MIX & GO” – masons mortar

Thanks!! That is what I will use. As I said above. They are local to me and under £20 for a 25Kg bag!!

 

[pgrbff]

A big thanks!! I just did. They are local to me, prices look very very good and they have a fantastic range of products. I would just go for the premixed. I can take a sample stone along and match the colour

When i first contactedthem I was in Ireland. Rather than sell me lots if expensive peoduct with huge shipping costs they taught me how to make my own. Back then I was using fat rather than hydraulic mortar. I cant praise them enough.

 

[Sandyn]

You can stuff the job much easier by trying to do it on a dry summer day without enough water than you ever would by worrying about mixes

I will leave the job for a few weeks until the weather will is more suitable. Everything dries so quickly just now.

 

[davethebb]

Over the years I have undertaken a fair bit of work on historic buildings including repointing and rendering in lime. The first thing to note is that there are two main types of lime that are now used in historic buildings; the first is pure slacked lime, lime, or lime putty, and then the general NHL mixes. NHL (Natural Hydraulic Limes) will set under water like modern portland cement). NHL lime is a mix of lime of various proportions and quality along with impurities from the limestone rock used to manufacture it. It is these impurities (effectively act as Pozzalans) that make the lime go off. NHL Limes are easier to work with as they will recarbonize (set) quicker so you don't have to be so careful with the moisture level after the work is carried out.

Pure Lime/slacked lime/lime putty is just that. You mix it with the relevant proportion of sand a use. This is the traditional lime mortar/render. NHL is between this and modern portland cement.

Two important things to remember. Firstly Lime will burn you so wear gloves and goggles. Also, use the correct sand for both pure lime and the NHL's - do not use sand from a builder's merchant. You should use sand that is from a local quarry as this will give you the color and texture you will be after - you will need to experiment. It is also very important that the sand is washed (no salt) - if you don't it will fail very quickly.

Just one further note on NHL mixes. Although there are general rules for these regarding the mix ratios these must be taken as a guide. You will see some NHL suppliers will have a higher level of lime vs others and therefore the mix needs to be adjusted - a lot of the cheaper NHL suppliers use low lime levels and therefore you need to reduce the sand content according to otherwise it will fail very quickly.

Hope this helps.

 

[pgrbff]

As long as it’s above 5C you’re OK. Get yourself some hessian, use damp to slow the set and protect from heat and wind. Make sure the background is well wet down before starting.

 

[pgrbff]

We had to use lime mortar for our grant aided roof repairs (conservation area). It washed out from between stone ridge tiles and coping stones in no time at all and needs redoing.
OTOH where used as pointing on vertical limestone walls it seems to be lasting.
A neighbour in the village had whole house rendered and painted by another conservation expert who supposedly specialised in slaked lime trad finishes , but it failed dreadfully after 2 or 3 years and was a disaster.

Maybe try using an NHL 5 on the roof, if the roofing material is not too soft. I used it set chimney pots in Ireland and it was fine.

 

[Jacob]

......

Pure Lime/slacked lime/lime putty is just that. You mix it with the relevant proportion of sand a use. This is the traditional lime mortar/render. .......

As I understand it, in Derbyshire slaked lime was used straight from the kiln with no mixing. The pozzolans and other stuff was there by chance. You can see bits of coal, ash etc in old mortar. I think modern attempts to copy it maybe failed and people reverted to using mixes with dry bagged hydrated lime - which has always been used anyway, were available. And portland cement mixed in too. Basically a completely different mortar.
But it's not my trade!

 

[pgrbff]

We had to use lime mortar for our grant aided roof repairs (conservation area). It washed out from between stone ridge tiles and coping stones in no time at all and needs redoing.
OTOH where used as pointing on vertical limestone walls it seems to be lasting.
A neighbour in the village had whole house rendered and painted by another conservation expert who supposedly specialised in slaked lime trad finishes , but it failed dreadfully after 2 or 3 years and was a disaster.

There is no reason hydraulic lime mortars should fail if applied under the right conditions. It is far more difficult to use fat lime mortars and they need much more care in preparation and care after placing to ensure they do not dry out in the first couple of days or even 7/10 days. If you can keep a fat lime mortar soft for the first day and continue looking after it in the same way, it will start to set up very slowly.

 

[pgrbff]

We are re working some brick panels set within oak frame that we did 14 years ago, the main panel is fine but the perimeter has cracked as the oak has moved, I had to submit samples for the LBC originally which was a mixture of brown building sand, brown sharp sand and the HNL. The brown sand is no longer available so I had to drive a 2 1/2 hour round trip to find some AHH. Red sand is readily available but would look very pink in comparison the the old stuff.

https://www.bromfieldsand-gravel.co.uk/brown-building-sand
I have bought some goat hair to add into the mix to help prevent it cracking, usually used in lime plaster mix but thought I would try a sample-hopefully be stronger if the hair isn't too visible.

@julianf have you used goat hair within a pointing mix? I know its unusual....

https://www.lime-mortars.co.uk/lime-plaster/natural-goat-hair/500g


Cheers

Peter

Be sure to add it in small quantities very slowly or you will get clumps in the mortar.

 

[pgrbff]

The bags of lime mortar are the easiest way to get consistent colour, as above, in France its only the Brits who source the sand and lime separately and mix it themselves. Available in various colours from tan too grey, in most of the shed type DIY stores, I'm sure it must be available in the UK as well.

I minute search: DRY BAGGED LIME MORTARS – “MIX & GO” – masons mortar

In Italy it's fairly regional, Vimark sell a couple of colours of basecoat to match the local stone. It is incredibly easy to use compared to mixing your own in the UK. It is as easy, or easier than using sand and cement as it is very fatty. They must cheat and add all sorts to make it so easy to use.

 

[Jacob]

There is no reason hydraulic lime mortars should fail if applied under the right conditions. It is far more difficult to use fat lime mortars and they need much more care in preparation and care after placing to ensure they do not dry out in the first couple of days or even 7/10 days. If you can keep a fat lime mortar soft for the first day and continue looking after it in the same way, it will start to set up very slowly.

It seems that our local experts and suppliers didn't know what they were talking about.
I guess you need to buy the right branded stuff ready mixed and known performance, or it can go wrong.

 

[pgrbff]

As I understand it, in Derbyshire slaked lime was used straight from the kiln with no mixing. The pozzolans and other stuff was there by chance. You can see bits of coal, ash etc in old mortar. I think modern attempts to copy it maybe failed and people reverted to using mixes with dry bagged hydrated lime - which has always been used anyway, were available. And portland cement mixed in too. Basically a completely different mortar.
But it's not my trade!

When I first started I used to collect 1.5 tonnes of freshly slaked lime in a digger trailer straight from the kilns. The wife and I would line the trailer with two layers of heavy plastic sheet and pray it didn't rain. When we got home we would mix it with sand in a mini belle, add water and watch it boil. We would pour the resulting mortar in a wooden "ark", 16'x8' made out of scaffold planks, and let it mature a year or so before knocking back with a rollerpan mixer I towed to Ireland from Wales.

 

[Jacob]

When I first started I used to collect 1.5 tonnes of freshly slaked lime in a digger trailer straight from the kilns. The wife and I would line the trailer with two layers of heavy plastic sheet and pray it didn't rain. When we got home we would mix it with sand in a mini belle, add water and watch it boil. We would pour the resulting mortar in a wooden "ark", 16'x8' made out of scaffold planks, and let it mature a year or so before knocking back with a rollerpan mixer I towed to Ireland from Wales.

Well there you go! Nobody told us any of that!

 

[pgrbff]

It seems that our local experts and suppliers didn't know what they were talking about.
I guess you need to buy the right branded stuff ready mixed and known performance, or it can go wrong.

Before I moved to Italy I would buy NHL 3 and 5 hydraulic lime, St Astier, and mix it myself. It was definitely more difficult to use than the European ready mixed varieties but if you made sure the background was damp enough, to stop the water being immediately sucked out of the freshly applied mortar, and you kept it damp by regularly misting, and kept the wind and sun off, it would be fine.

 

[simoncmason]

I have been restoring an old farmhouse and barn in central France over the last 3 years. All the mortar round here is lime, so the local builders merchants are full of it. We have used mostly NHL 3.5 with NHL 5 on one more exposed area as recommended by an experienced builder.

I mix it in a normal cement mixer.

Things I have learned after doing around 120 linear feet of 25 foot tall wall.

Get the stone work wet, really wet, then wet it some more. (This is on granite, so may well vary on softer stones - you'll probably need to wet it even more if the stone is more porous).

Mix it for at least 30 minutes. Start with it looking on the dry side - you'll probably think it is too dry, leave it mixing, check after 20 minutes - it will look wetter than when you left it, you can always add a little (very little) bit more water to the mix at this point.

Wear a good quality face mask and safety glasses or goggles - I use one of the jsp press to check masks - when putting the dry lime into the mixer and keep you mask on until you have added the water and you can see it has stopped dusting. It is really nasty stuff when dry.

Wear gloves the whole time you are working with it, it will dry and crack your skin and leave you with sore hands.

As you are pointing each new area wet it down again - I use a pump up garden sprayer set to a fairly fine mist - you will find it much easier to work and it will stick a lot better when wet.

If you are working in direct sun, shade it - it will dry a lot slower and last a lot better.

On granite it brushes off quite easily after 24 hours - the way the French do it round here is basically to slap it on all over and then brush it off. I can't bring myself to do that - and use pointing trowels and keys - which wastes a lot less - but it is easy to brush off. But if your stone is more porous it may well stick a lot more.

I've found it more forgiving and nicer to work with than cement, it's hard work but enjoyable and rewarding once it is done.

 

[Peter Sefton]

Thanks @simoncmason sounds like very good advice.

Cheers

Peter

 

[Jacob]

Lots of advice on here. 20 years ago when starting mine there was not much advice at all. I even went on a 2 day SPAB course but with hindsight they were beginners too.
A lost tradition in UK but still going strong in France?