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Lime mortars


Kilt

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I know this is probably a can or worms.. but hey ho, here goes.

I’ve been trying to get my head around the various types and processes of lime, so my understanding is prob going to be a bit wrong. ?
 

I’ve a 19th century rubble wall on my property I need to repair, before it falls down..
I’m a bit torn on which way to go with mortar, most sympathetic v’s ease of use v’s effectiveness  . 
 

I was going to go with simple NHL 2 or 3.5, but been recommend higher grade (pure) lime using a pre-mixed lime putty mortar mix... I like the simplicity of the pre-mix and easy storage..

There’s also the dry, pre-mixed pure-lime NHL bags, but they seem even more expensive. 

 

Anyone managed to get to grips with Hot mixes?

Would love to get up to speed with that.. but seems to be a bit of a dark art, even though straight-forward process, (on paper), if not a bit explosive! ?

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Hello,

 

Yes, lime does open up a whole can of worms. Even within the lime community. The best info I've so far found about lime comes from a little book called Lime: A Practical Guide by Jane Schofield. You can buy is for £4 from the Society for the Protection of Old Buildings: Lime: A Practical Guide

 

This guide explains all the types of lime but focusses on the non-hydraulic, i.e. lime putty, and will no doubt cover everything you'd need to know about the mortar mix and process of repairing your walls.

 

HTH

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2 hours ago, Kilt said:

I’ve a 19th century rubble wall on my property I need to repair, before it falls down..

 

IMO, there are cases where pure lime mortars are recommended e.g. when you are matching on a listed property, but the making and execution of lime mortar pointing is quite specialised.

 

Our last property was a farmhouse that was a mix of 1700s - 1900 stonework, and we repointed all the stonework.  An old boy helped us in the early days and we followed his advice.  The main thing is that the mortar must always be softer than the stonework being pointed. We kept to a 1:3 cement: soft sand mix, but the cement was a mix of fresh lime and Portland. We found a 2:1 mix of these worked best for our stone, hence it was a 2:1:9 mix lime:Portland:sand. You could work this for up to 4-8 hrs depending on temperature, and brush out excess after maybe 6-12, again temp / direct sun dependent. It would start to harden properly after maybe a day. You will need to experiment with technique: rake out, wet, point, brush out; all spaced out according to hardening rates. Work from top to bottom.

 

The colour is a light grey rather than the paler pure lime mortar. This job was spread over 33-25 years ago. We still live next door to this house, and the stonework / pointing still shows zero sign of degradation. 

Edited by TerryE
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1 minute ago, TerryE said:

IMO, there are cases where pure lime mortars are recommended e.g. when you are matching on a listed property, but the making and execution of lime mortar pointing is quite specialised.

...

 

You can say that again. For a start, Hydrated, hydraulic or non-hydraulic lime?  The following table comes from https://www.lime-mortars.co.uk/lime-mortar/guides/lime-hydraulic-or-non-hydraulic

 

Hydraulic Non-Hydraulic Cement (OPC)
Breathable Yes Yes No
Setting Speed Medium Low High
Flexibility Medium High No
Durability Medium Low High
Labour Low High Low
Cost High Medium Low
Shelf Life Medium High Medium

 

Why do posts about succesful lime pointing always involve '... an old boy ...' eh?

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5 hours ago, TerryE said:

the making and execution of lime mortar pointing is quite specialised.

I’m not entirely sure that is true. There is a bit of a mystique about it but I’m not sure it is justified. It is just that cement has taken over for so long that most Brickies can’t cope with something new.

For someone new to pointing I would say using lime is easier than cement since you have more time to play with. There are also a few other differences. Dampen the stone you are pointing, keep the wall damp/covered if you can after the mortar is in. 
 

I would go for hydraulic lime 3.5 and sharp sand (1:3). Getting the right amount of water is key for repointing. You want it dry enough to not smear over the stone. Make sure you rake out enough, push the mortar in firmly and don’t be too fussy to get it looking right. Wait (sometimes a day later if not too dry) till it is ready to rub over ( I use the back of a churn brush that I have shaped to suit the stone) and make sure it is all pressed into place properly. Wait again till it is ready to brush over (I use a soft brush as I don’t like seeing brush lines). I can see the appeal of lime putty as you don’t have to mix up but it is more expensive.

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18 hours ago, ToughButterCup said:

 

You can say that again. For a start, Hydrated, hydraulic or non-hydraulic lime?  The following table comes from https://www.lime-mortars.co.uk/lime-mortar/guides/lime-hydraulic-or-non-hydraulic

 

Hydraulic Non-Hydraulic Cement (OPC)
Breathable Yes Yes No
Setting Speed Medium Low High
Flexibility Medium High No
Durability Medium Low High
Labour Low High Low
Cost High Medium Low
Shelf Life Medium High Medium

 

Why do posts about succesful lime pointing always involve '... an old boy ...' eh?

Thanks. Very helpful for quick guide, will check out the website too. 

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12 hours ago, jfb said:

I can see the appeal of lime putty as you don’t have to mix up but it is more expensive.

I was more interested in the quality of the lime, that comes in the pre-mixed, the fact you don’t have to measure etc, is a Brucey-bonus!

Also ability to keep is stored in “stasis” is highly appealing to a self-builder/DIY’er.

 

But as it’s just (just?? ?) a 10x3m garden wall, it’s not mission critical and I’m not under any “listed building” planning/conservations restrictions. 
However the garden wall is same material as my house, so it’s a bit of an acid test. The house will need doing next. 
 

I’m having our Gable-End harled (hot lime) and lime-washed in the Spring, so will try and pick the contractors brains, however they’re (quite rightly) not going to spill beans and do themselves out of a job. But like a lot of us, I don’t have unlimited funds. 

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I’ve used both the pre-mixed, came in a tonne bag and quick lime slaked on site to putty and mixed using local sand, as would have been the case when the wall was built. If it were me I’d go for a ore-mixed tonne bag, it just so easy to throw a few shovel fills into a mixed at the start of the day, to knock it up! I use a selection of pointing irons (by width), roughly point the lime into the joint, once the section is finished, knock the pointing back using a churn brush. Job done.

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21 minutes ago, Triassic said:

I’d go for a ore-mixed tonne bag...

Thanks for your thoughts. 
 

how easy did you find it to store the 1T bag, once opened? Did you work through it pretty quick?

 

if I was going to go with pre-mixed, (which I think I’m leaning towards), I was going to take hit, and get smaller bags. I’ll be working on my own, so I was worried about a 1T bag opened for a long duration. 

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On 21/03/2021 at 22:11, Triassic said:

The pre-mixed lime mortar comes in a plastic bag inside a builders one tonne bag. If you keep the plastic bag sealed the mortar will last for up to twelve months.

?

 

good to know. 
 

 

cheers. 

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