Repointing using lime mortar

[Sandyn]

Anyone done it? I would like to repoint some parts of my house, using hydraulic lime, but it seems difficult to get the mix right and lots of scope for failure.

 

[rogxwhit]

Look here - Lime Pointing | How to Re-Point with Lime Mortar | Guide Sheet & Video

You might be able to source NHL lime through a local builders' merchant (Jewson et al) - I have done in the past - and get free delivery. From Mike Wye and others I expect it would be a pallet delivery with associated charge. Good site for info though. Then there's the aggregate ...

 

[julianf]

As with pretty much anything involving renders etc. you will find a lot of variation in advice on mixes.

The main consideration for you is that the mix is the colour. Unless you go too far off the beaten track most of the options for lime will work.

The basic mix that you see quoted often is 1:3 nhl3.5 to sharp sand. But there are stacks and stacks of variations on this.

Be aware that "sharp sand" is hugely variable. I will buy sharp sand from different vendors depending on the job that I want to do with it.

 

[Sandyn]

Thanks!! it's portrayed as being difficult to do. Mixing correctly seems important.
I've been searching and of course Amazon sells it Think I'll get a bag and try a test patch. The video is good thanks. Do you remember what mix you used?? I do have a really good facility near me, so will search their site and see what information is there. I found this guide to lime mortars on the site. I need to read it to get all the terminology understood better.

 

[Sandyn]

The basic mix that you see quoted often is 1:3 nhl3.5 to sharp sand. But there are stacks and stacks of variations on this.

Be aware that "sharp sand" is hugely variable. I will buy sharp sand from different vendors depending on the job that I want to do with it.

Thanks, I'm planning repointing parts of an old house, so the colour is reasonably important, but not critical. I think some kind of white sharp sand may be suitable, or a mix. Is there a brand of sharp sand that you could recommend?
My fear was that I would do the pointing, then 6 months later it starts falling out or some other problem because I didn't do something right in the mix or after applying.
I have one gable end which was repointed years ago using cement. I would like to re-point that wall. The other west facing wall has lime mortar (I'm sure it is) and it has survived the weather better than east. The west wall gets all the bad weather.

 

[Stuart Moffat]

I’ve done it, and continue to do it from time to time, but I haven’t mixed it yet. The good thing about lime mortar is that it is reversible, unlike cement.. About 12 years ago I paid a builder who almost exclusively works on listed buildings to do some repointing on our (not listed) house. He first mixed up about 4 samples in slightly different shades, and left them alongside the walls to be done to weather for a month or so. He then mixed a significant amount of the chosen mix for the job. At the end of it there was enough left over to put in a 30 litre tub which he left me. it has remained good, and just needs to add a bit of water to the tub each time I open it, and work it to the right consistency.

 

[Peter Sefton]

Hopefully going to undertake some lime repointing on our barn soon, going to use 3.5 HNL which is readily available from our local builders merchants, the bigger issue was getting hold of brown building sand which has become very rare in our location.

I like this guys videos



Cheers

Peter

 

[Lorenzl]

I am currently in the process of buying a house that is in need of a lot of repointing so it will be a learning process for me as well.

I will buy sharp sand from different vendors depending on the job that I want to do with it.

We built a bungalow years ago and the father in law was a very experienced bricklayer, We wanted a raked joint for contrast as the bricks were yellow and most mortar is quite light in this area. He recommended not doing that as it would hold water - there is a similar type of joint that wont hold the water. Instead he brought sand from a supplier that wasn't washed and it produced a lot darker mortar.

 

[MikeJhn]

Take a trip to Leroy Merlin in France: https://www.leroymerlin.fr/produits...intoiement-ton-pierre-prb-25-kg-57189881.html may even be available in the UK?

 

[julianf]

Is there a brand of sharp sand that you could recommend?

In short, no, as it's dependant on what's about in your geographical location, and what matches with the building materials present.

You're more or less looking at how well (or otherwise) graded it is, and the colour.

When you look about online you will see people adding "stone dust" and other variants, but, really, it's more to do with what people have on hand. You would need to stuff it up quite badly indeed to be "redoing it in 6 months"


If we are getting to precision, you're matching the mortar to the block and to the exposure. You should always use a softer mortar than the block and, technically, a greater permiability.

NHL is way "stickier" than Portland cement. If you go with NHL be aware that if you sling it everywhere, thinking you'll clean up later, it will stick. Also watch out that some red sands can be really quite staining, esp when teamed up with the lime.

Have a look at what sand is available to you. Find one you like the colour of (remembering the lime will make a redish sand pink, lighten up a yellow, and make a white whiter) and make sure it's graded reasonably for your application. Even going to get a few 25kg sacks from the various mainstream DIY places near you and you will see massive variation between what wicks might sell and what b&q have, as they're all buying out of different holes in the ground.

Find one you like, buy a bag (or find one that's been dropped / split in the store!) and see if it's full of pebbles or fairly uniform.

Maybe buy a 25kg bag and a bag of lime and mix some up and have a bit of a play before buying a whole load?

I have a fair bit of experience with lime, am a lvl 2 qualified plasterer, etc. but, again, even with "out of the bag" modern mixes (gypsum etc) if you ask 4 plasteres some technicality, you will get 4 different answers. When you get onto less common materials you will get many more answers.

This is largely because people do things differently / how they've always done them etc (not necisarily wrong, just with variation) and also as buildings are so different. And different in different areas, with different environmental considerations, local materials etc.etc.


But, again, unless you try and do something whacky, a basic mix won't do you far wrong.

 

[Jacob]

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.

 

[Jacob]

.

 

[Sandyn]

You would need to stuff it up quite badly indeed to be "redoing it in 6 months"

Thanks, That's what I wanted to hear. I was afraid it was a real dark art and if you didn't do things right it would fail early.

 

[Sandyn]

the bigger issue was getting hold of brown building sand which has become very rare in our location.

Is the choice of sand to get the colour right, or other reasons?

 

[rogxwhit]

A fine earlier thread here - Lime mortar

 

[Jacob]

Thanks, That's what I wanted to hear. I was afraid it was a real dark art and if you didn't do things right it would fail early.

See above. It may fail early even when done by experts.
I'm a big believer in trad conservation and methods but I think it may be a lost art with a huge element of luck involved. We were later advised to always add a good proportion of portland cement to avoid future disappointments!
The stuff we used was made locally but didn't look anything like the traditional stuff on view in countless old buildings in this area.
PS we live in the heart of the limestone industry, we have old lime kilns all over the place (quite small a bit like pottery bottle kilns only made of limestone) even a pub called The Lime Kiln. The burnt lime was used direct after slaking without mixing sand or anything and was obviously highly effective. But it seems to be a lost art.
OTOH mixing ordinary hydrated bagged lime with cement and limestone chippings-to-dust makes a good fake mix

 

[Peter Sefton]

Is the choice of sand to get the colour right, or other reasons?

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

 

[julianf]

Thanks, That's what I wanted to hear. I was afraid it was a real dark art and if you didn't do things right it would fail early.

I care for my tools, but, even still, if you're doing gypsum all the time, you'll get build up on the trowels. I guess gypsum has so many washing cycles, and you're always trying to get things done quick...

Anyway, if you then soak a trowel with gypsum residue in water overnight, you can wash / scrape off the gypsum.

Ill have to admit that my stepladder (that, essentially, lives outside) will have NHL residue on it from jobs years back.
You only leave it on a paddle mixer once, thats for sure.


One possible screw up -

I don't know what surface this is going onto, but wet it down way more than you think you need to. And dont even think about doing it in a heat wave.
If nhl dries too quickly it will be weak. You'll see renderers hanging hessian sheet to control the drying. A later autumn or spring job and youll be fine, but don't do it when the sun is beating down.

I should have said this before, but was far too focussed on ingredients. 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.

 

[1steven]

I am just about to do the pointing on our Croft plus three out buildings. Will just in a corner out off view and hopefully will get better and the job goes on. Also have internal fireplace to do. Found a very informative video on YouTube.

 

[George B]

The Restoration Couple on YouTube have quite a bit on lime and used Lime Plaster, Putty, Mortar, Limewash & More | Limebase, found their videos useful and have a bit of repointing on my to do list.