Repointing walls – a factsheet awaiting your contributions
20th April 2005 at 13:06 #729035
previous_webmasterMemberJoined: 23 Nov 2002Location: Bristol, UKTotal posts: 15
Calling all masons, artisans, or those with repointing experience.
Following a discussion elsewhere on repointing, and my bemoaning the fact that we lack a good fact-sheet on this popular subject, Barry has kindly put together a document as a starting point.
I would be most grateful if people could look through it, and then make constructive suggestions for amendments, additions, tips, etc that will ensure that the fact-sheet is as accurate, and applicable to the widest scope of implementation, as possible.
When all comments have been logged, I’ll attempt to incorporate them into a full fact-sheet on this much-sought-after subject.
Pointing stone walls.
These are of course only my views based on very limited experience (didn’t do much pointing as a mechanical engineer) but I’ve attempted to write down the basic reasons, methods and materials that are used for pointing old stone walls. Naturally other people will have their own preferences and ideas but at least it puts down a basis to work from, comment on etc. I am sure there will be bits that require adding but at least it gives you a starting point.
I understand that lime and cement are at opposite ends of the spectrum as regards to water ingress or porosity. Cement at the one end is impervious to water whereas lime, at the other end, allows water to pass through to some extent and therefore allows the stone to breathe. Water is absorbed into the stonework from the ground as well as from the elements. (rain, etc.) With a lime-based joint, the water can escape through the joint whereas with a cement-based joint, the water can only escape through the actual stone.
This ‘breathing’ of the joint causes the joint to erode over the years and re-pointing the joint will then be required.
There are basically 2 types of lime:
1. Non-hydraulic lime (aerienne), which sets over a period of time on contact with air.
2. Hydraulic lime, which sets on contact with water.
Available lime (free lime) in the product is important for workability, self-healing properties and elasticity. It will also contribute to final strength. Free lime will allow some tolerance for initial structural movements. Natural hydraulic lime mortars will therefore offer adequate strength with enough plasticity to accept slight load shifts.
Natural hydraulic lime (NHL) is the most common type sold in the DIY shops.
They are given an NHL number and have a corresponding level of free lime.
NHL 5 has a free lime quantity of 3%
NHL 3,5 has a free lime quantity of 9%
NHL 2 has a free lime quantity of 15%
When non-hydraulic lime is mixed with water, lime putty is formed. If you have to make any, always add the lime to the water slowly. Never add water to the lime as this can cause the water to boil.
Using a mixture of cement, lime and sand is called ‘gauging’.
White cement (ciment blanc) is the type used.
The reason why cement is added probably stems back to when cement was introduced. Because the non-hydraulic limes took several days or more to set, cement was added to obtain a faster ‘set’ and in effect achieve the characteristics of the hydraulic lime available today.
However, it must be borne in mind that the mixture should be slightly softer and more porous than the stone so that any problems that may occur such as cracks will only affect the joints themselves which can be re-made, and not the actual stone work.
I live in an area where the golden stone is ‘soft’ and consequently only use lime and sand.
If the house was made of say granite, very hard and relatively water resistant, then perhaps some cement could be added as it would not affect the wall’s capabilities to breathe.
I believe a gauged mixture of 1 cement, 3 lime and 12 sand (1:3:12) would be a reasonable mix in this case.
Lafarge make a number of limes such as Crualys, Chaux Blanche, Tradifarge, Frescalys and Parex.
Crualys NHL 2, is a Hydraulic lime. It is especially intended for use on old buildings for mortar, jointing and rendering.
Chaux Blanche NHL 3.5, is also a hydraulic lime used for jointing.
Tradifarge NHL 5, another hydraulic lime, is used for making mortar for block work.
Frescalys is an aerienne type lime and is used for lime washes (or whitewash as I used to call it.)
Parex type Monexal and Monorex are a cement, lime, flint and sand mixture used for rendering mortars.
I understand that a ratio of 1 lime to 3 sand is about the correct mix for jointing. Too much lime will cause the lime to be washed out and stain the stone work, possibly causing frost damage.
Too much sand and the mixture will not set correctly.
Personally, I use the Crualys and have found good results with a mixture nearer to a 1:4 sand mix.
Wear good gloves whilst cleaning out the old mortar.
Raking out the old mortar is a real dusty job and it helps if you spray the area with water first using a garden sprayer.
Allow this to soak in and then rake out the loose mortar to at least a depth of twice the joint width.
If the mortar is really old and crumbly, keep raking it out until you reach a reasonably firm surface. I use an 8″ flat blade screwdriver and have been in to full depth in several places.
Clean out any loose remains etc and then spray again so that the stone is damp.
If the holes are large, then start to find small stones that will fit into the crevices and place them in a handy position.
Mix or ‘knock up’ as builders say, a bucketful of dry mortar in the correct ratio. Ensure the two parts are really mixed together.
Add water and mix until a pliable mixture is obtained. The more you mix it, the better the consistency and the easier it is to apply.
Spray the joints and wall again and then apply the mortar.
Using a hawk board and a pointing spatula, push the mix firmly into the joints.
For the larger holes, apply some mortar, then push a stone in and then apply more mortar.
Fill the joint until it is slightly under flush by about 5mm. It doesn’t need to be struck at an angle as it is not intended to shed water like a cement joint.
Leave this for about 20 minutes and then go over it with the spatula to achieve a good finish.
After about 3 hours (your own experience will dictate this amount of time) brush the joints to clear any smears off the stone work and to improve the contact between the edges of the stones and the mortar. Brushing too soon will put brush marks in the mortar and brushing too late will prove to be hard work.
Hope this is of some use.
20th April 2005 at 14:11 #778949
- This topic was modified 04 Sep 2014 14:36 by Char.
My total lack of experience means I cannot offer much in the way to facts in the sheet. However, it might help to give you the questions I have after reading the sheet.
The Chaux Blanc has instructions for different Sand/Chaux Blank mixtures (for different applications) on the sack. All measurements are number of buckets of sand per sack of Chaux Blank. I have a few sacks around, but instructions are in French so it probably would not help the fact sheet much.
Does Chaux Blanc contain any cement. It seems to set in a reasonable timescale, etc.
I’m a complete amateur and have loads of problems getting cement/chaux/anything to stick to walls (e.g. when plastering them). I’ve done the water spraying, etc. but still have problems. I was once told in the UK to add washing-up liquid. Don’t know if this helps or not (or if there are other tricks or if failing to stick means too dry/wet).7th June 2005 at 21:13 #778950
divvylivvyParticipantJoined: 31 Jul 2003Location: Charente 16Total posts: 143
Chaux blanc does not contain cement it is just lime. Tradifarge do do a ciment/lime mix that we have used succesfully internally and externally. Though in the colder weather it takes a little longer to go off and slows down your work.
Pointing is a long job and you need to brush your joints before they set with a soft hand brush to take away an excess material.
ALSO when dealing with Lime based products – wear gloves, face masks and goggles – ciment and lime can cause burns and lime if ingested will make you proper poorly.
If you have troubke using trowels, then do what our friend did and point your walls with your hands, wearing marigold gloves for protection – you get and excellent fish (after brushing down – can get into small crevices and dont lose so much mix on the floor.
Hope this helps
Is that all?9th June 2005 at 11:24 #778951
oconnaMemberJoined: 09 Aug 2004Location: N/ATotal posts: 1
I posted this before in relation to pointing interior walls – hope it is of some assistance
1. Sprayed the walls lightly with water to keep the dust down.
2. With wire brushes scraped out all loose and excess debris and general dirt , cobwebs you name it. This was quite hard work – you need to buy good wire brushes because the cheap ones wear out. Better to have too many then too few – nothing more frustrating than not being able to continue because you have no equipment. We wore gloves, dust masks, and goggles although the goggles tended to steam up.
3. I went to the local Bricomarche and got sand which was basically builders sand (and the only one they had) and lime (chaux blanc). This was mixed approx 3:1, Sand:Lime. I bought a wheel barrow (about €30) and used this for mixing – I would recommend this because you can move it round and it is not at ground level. The mixing is a bit of a knack but you tend to get a feel for what is the right consistency ie not too thick not too runny. Used a combination of a shovel and a large trowel to mix. Then put a shovel of this onto a hawk and slap it into the gaps with trowel.(a hawk is flat board with a handle underneath – you can make them yourself from old wood). When it come to the trowel I would recommend you purchase what is called a “langue du chat” ie a cats tongue which is a long, light, narrow trowel with a rounded end readily available in the Bricomarche. When you are throwing it onto the wall my advice is not to be sparing – what falls on the ground you can gather up and put back into the mix
4 . When the mix has started to dry out after a couple of hours start to brush back with your wire brush to expose the stones. Again you will get a feel for what is the right amount of pressure to apply without undoing all your work. Again most of what you brush off can be put back in the mix.9th June 2005 at 12:01 #778952
previous_webmasterMemberJoined: 23 Nov 2002Location: Bristol, UKTotal posts: 15
Thanks for these contributions. Please keep your pointing tips, instructions, and advice coming.11th June 2005 at 16:44 #778953
My recomended mix would be three parts soft sand one part sharp sand one part cement also if you like you can add a colouriser. use farely dry as so as not to stain the stone. also add a very little fairy liquid and you will find your mix more plyable. I have pointed many many yards of crazy paving in my time and find this method the best. Peter.13th July 2005 at 17:10 #778954
mukkaMemberJoined: 12 Jul 2005Location: N/ATotal posts: 1
Hi all,a bit late to your articles but here we are.If you have an older property,you must add lime to the mix.Older properties were built using lime only.They are still standing now!Reason? The lime used to let the building move slightly yet still retain its strength.If you use only sand and cement,the building will not be able to move so easily,thus cracks will appear.In the late 80’s and early 90’s the buliding trade used mixes that were too strong and therefore the bricks or blocks broke instead of the mortar joints.Hope this is not teaching any of you to suck eggs!
I keep running but never seem to catch up!15th October 2005 at 15:50 #778955
jppfranceMemberJoined: 21 Jun 2005Location: Montcuq (46)Total posts: 1
There’s a British government factsheet available at http://www.mineralsuk.com/britmin/mpfhydrauliclimes.pdf
I came across it when trying to find out more about NHL 3.5z. The addition of the letter z confused me. Point P in Prayssac only had the z version available this morning so I thought I’d check it out. Seems that the z denotes the addition of pozzolanic material for greater strength.27th December 2005 at 15:59 #778956
i had agreat deal of difficulty getting the mortar to stick, i thought afterwards that the cement i used had no plasticiser in it as walcrete would have in uk,
so unless anyone knows if you can buy a plasiciser i will take a can of febmix with me on my next trip, washing up liquid has a detrimental effect on the mortars strength and was always frowned upon when i was building(20 years ago) hope this helps.20th January 2006 at 17:31 #778957
mark59markParticipantJoined: 23 Dec 2004Location: N/ATotal posts: 137
I have found using a rotary hammer drill with a “burnt out” masonary drill – (we all have one of these which the tungsten tips are missing in our boxes don’t we)? ideal for removing old chaux / mud etc from the gaps between stones in a wall. GOGGLES ARE ESSENTIAL FOR THIS as bits of old chaux fly out at high speeds.
As regards to rendering – I use the “chuck it at it” method – using my hands (heavy duty gloves) to direct the chaux where it’s needed. Yes this is messy, but the chaux goes deep in the joints.
The next morning I brush away the excess chaux using a wire brush If the chaux is getting hard I will using a rotary wire brush (GOGGLES ESSENTIAL).
Tip. If you clean the area below the wall and/or place a sheet there to catch the brushed off excess chaux – this excess chaux can be used again to fill in the odd hole etc, by re-hydrating it with water!
My mix is 10 parts sharp / river sand, 3 parts chaux and 1 part white ciment – the latter hastens the drying process.
Mark.20th January 2006 at 17:36 #778958
mark59markParticipantJoined: 23 Dec 2004Location: N/ATotal posts: 137
Sorry I forgot to say that before I start rendering I water the wall and joints (old chaux and mud) using my large garden sprayer.
Mark21st February 2006 at 23:29 #778959
lostinfranceMemberJoined: 07 Sep 2005Location: Centre Dept 36 Near ArgentonTotal posts: 1
For raking out the joints, use a small lengh of copper tubing ( 2 foot) with a slight bend on one end (for an handle) and flatten the other end about an inch or so from the end. After the a while, the end will “round off” and you have the perfect joint tool.16th March 2006 at 11:07 #778960
petercherryParticipantJoined: 02 Sep 2005Location: Derbyshire & La CreuseTotal posts: 40
A bit late on this one .. I was speaking to a Welsh stone mason on my last trip over to France and was talking about pointing. He closely desribed Marks method, pushing it in with a large pair of the thickest rubber gloves you can find, but it was the mixture that he said was important.
He said you should use a mixture that when you put it together to form a ball in your hands, it should only just stay together. This way he reckoned the mix would not stain any of the stone-work. I think he siad that he wetted it after with a sprayer.
He also said that he did not believe in lime mixes, he used 3:1 sand cement …? His argument being that they only used lime in the old days because that is all they had to hand …? I tend not to agree with this, but I thought his idea of using a dry’ish mix was interesting – I have yet to try it out …
Peter21st March 2006 at 23:20 #778961
ok have been trying all of the above methods for 4 days now and none have worked for me …..
so i have thrown away my float and bought a gauging trowel , i now use cement au calciair mixed 3.5- 1 . mix it in the mixer so it drops off the back clean i.e. not to runny and not to dry . soak the walls with a garden sprayer and when i think it`s wet enough I wet it again .
then just load the hawk up from a spot board and lay on a scratch coat starting from the top left hand side ( i am right handed ) push it well into the joints and leave it alone ………
next day scrape down to the stone and feather it it in
a lay mans method but it works for me
dave2nd August 2006 at 19:06 #778962
thebeansParticipantJoined: 11 May 2006Location: Cantal, AuvergneTotal posts: 289
I am currently working for a french builder and after taking all the old joint out with a hammer and chisel and a small kango for the harder stuff (usually sand and cement patch ins) we then jet wash the wall, getting as much of the dirt and crap out of the wall as possible is very important. It is possible with a large water sprayer (i use one) but you have to really wash it down well and again before you start pointing. The guage we use is 6 buckets of sand to one bag of lime and we add water proofer (hydrofuge de masse pour enduits et mortiers). I think the hydrofuge is very good.I have pointed in our house with and without and have found that it retards the lime mortar ( stops it drying out to quick) hence you do not get the little cracks in the mortar especially in the larger joints. I use a hawk and a guaging trowel(english) and a small french pointing trowel. I also wear gloves and slap it in with my hands when necessary (dont be shy). have plenty of small stones at hand and hammer then into any large joints before pointing them as it will help stop the mortar sagging. As for consistuency, get it so it will stay on your trowel when you pick it up, not to runny not to dry in the middle. If you are slow its no prob you can just add water to the mix and bring it back. Fill the joint right up, dont worry about keeping the stone clean, slap it in and on. The finish is with a wire brush and i always wait to the next day. The brushes differ in hardness and it pays to have soft hard and medium at hand. Now you will see why it pays to get plenty on the wall as you can take the joint back as much as you want therefore revealing as much stone as you like. Start with the brush gently, feel your way into the mortar. To soon and you will pull it out, leave it to long and it will go off to hard! keep an eye on it, i normally find next day works best, but if its very hot brushing the same day may be necessary. Hope this helps
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