Repointing walls – a factsheet awaiting your contributions
8th February 2009 at 21:38 #779008
spongebobMemberJoined: 15 Feb 2006Location: N/ATotal posts: 1
hi i used nhl 3.5 with quarry sand. dampen walls first. wire brush off excess when ready.if too dry difficult to brush off excess if too wet and wall will stain https://i276.photobucket.com/albums/kk16/oldfrenchhouse/Picture031.jpg24th June 2009 at 02:50 #779009
As the work continues on the place we have perfected the technique and our mix is proving to look the part. It seems to get tougher as the months go by.
My wife now uses the compressor I bought with an air gun attachment and, wearing goggles and a dust mask, blows out any deep holes and then with a varying sizes of dowel crams the new mix in. She tends to put plenty of pointing on and then brushes the excess away with a soft brush until she is happy with the result. If we think that there is too much “staining we will sand blast the stone to bring it back however the stuff put on last year cleaned itself within a few frosts.
I tried the ponting gun inside but you only get to use about a quarter of a tube before it gums up due to the compression, no matter how wet the mix. I will be e baying that out.
That mix again if you have an old property that seems to be held together with mud is 3 sharp sand, 1 lime (gris), and one sieved torchis/mud that you have taken from the wall.
Only dead fish go with the flow28th August 2009 at 07:22 #779010
fiorowParticipantJoined: 17 Feb 2008Location: N/ATotal posts: 1
Hi All I have pointed my barn over the last 3 years & I tell you the best & fastest method of pointing is to don a thick plastic/rubber glove & simply push the cement off the hawk into the joint. By the time you have done 1m2 I would have done 2/3m2! Use the outside of your hand and apply the cement until the joint is full, with your fingers remove the surplus.
Look at the finish I got from exactly doing that.
barnconversionfrance.com If you want closes ups I can supply If you give me your email address.
Good luck Alan2nd September 2009 at 17:22 #779011
paulk11ParticipantJoined: 31 Mar 2009Location: PzTotal posts: 44
I’ve just spent the best part of 3 weeks repointing our place in Finistere with lime mortar and I have to say that it is a very satisfying experience.
I bought the lime premixed from the uk as I wasn’t confident enough to buy the ingredients in France but if I did it again I’d buy it in France and do it myself. I found out how to do the pointing by watching videos on Youtube – its amazing what there is available on there! It has everything.
I can’t believe that no-one has mentioned the Point Master gun? http://www.pointmaster.co.uk/ It has saved me hours and gets the lime deep into the joints very quickly and only rarely got gummed up. An absolutely brilliant tool and beats the other silicone gun type as it doesnt do your wrists in having to squeeze the trigger all the time. The mix needs to be fairly wet for it to work properly but I didn’t have any problems with it drying. There are a few cracks in it now but I think this is normal?
To clear out the old mortar, I used a jet washer which saved a lot of time but was messy! You must use gloves and goggles.
What I did was splodge the mortar loosely into the joints using the gun and my hands until it was just flush with the stones and then leave it for a few hours (good chance to get to the beach for a break!). After a few hours, go back to it and beat it into the joints with a milk churn brush and my fingers where necessary. If the weather is hot, you must ensure that you keep it moist as you don’t want it to dry too quickly. I then left it overnight and first thing in the morning I’d give it another bashing with the brush to push it further into the joints. If cracks appear after a day or so, you need to give this special attention and push the mortar into the joint with your fingers before it gets too hard.
It looks very new at the moment compared to the rest of the building but when its weathered it’ll look great.
Hope that all makes sense?
Paul2nd December 2009 at 19:55 #779012
Just read the whole thread, from start to finish, to see what’s been contributed, and I thought I’d throw in a few facts.
Firstly, Chaux Blanche isn’t strictly speaking Chaux (CaO). It’s a cement rich in Lime. The rest of it is a mix of Oxides of Silicium and Aluminium, commonly found in clay. NHL3,5 is the softest “Chaux Hydraulique” found in stock in most builders yards. This stuff is seriously hard when set, and it’s doubtful whether it allows a building to move or breath. NHL2 is where it’s at, and this contains a mix of Aerienne lime to soften it It’s what the heritage people use for their historic renovations. Chaux Blanche contains white cement, and is therefore opaque when dry. The resulting joints in one’s stone walls will appear flat in colour, and very pale. The use of colour additives to make up for this is just absurd. The colour of the joints is supposed to be natural, a mix of local sand, maybe some clay, and Chaux Aerienne, which is almost transluscent when dry.
OK, so for longevity, a lime pointing done with Chaux Blanche will last for years. It’s still a material of convenience, rather than an ideal.
The techniques for applying the various mixes given so far depend so much on the type of stone being pointed. As has been said, it’s essential that the mix is weaker than stone. In most cases this isn’t an issue except for limestone regions. Here though the stone still varies from the softness of blackboard chalk (it’s cut using a hand saw) to seriously hard where it borders areas of flint stone. ANYBODY WHO JETS WASHES A STONE WALL IS A MORON. This is why houses fall down. A leaky roof allows water into the walls, the mud that was used in the construction goes soft, the stone moves, then bulges, then collapses. There is no way to estimate the damage done to the core strength of a wall. It is idiotic to do this. The joints do not need scraping out to remove all loose material. This is holding the house up. A patio can be laid on sand, so stones can be set in dirt. You are aiming to achieve a joint where your pointing mix adheres well. It needs to be approx. an inch to an inch and a half deep. The stone must be moistened so that the mix doesn’t shrink on contact and lose it’s adhesion. For the same reason it needs to be dust free. A compressor and airline pistol does the job perfectly, although the dust cloud can be off-putting. No one has mentioned the grade of sand. It should be quarried sand, as coarse as can be found, 0/5 is good, but not always easy to find. 0/2 is useless, 0/3 is poor, 0/4 is fine. the oblique signifies a range of particles from 0 to 4mm for example, in 0/4. 04 is a monograde, also useless. The gaps between the particles needs to be filled with a bonding agent, so the bigger the gaps, the more Chaux you’ll need to give the correct consistency. It’s also why rendering with 0/0 sand (sablon), needs less Chaux than with a coarse sand.
The Lafarge guide give the mix ratio at 10 buckets of sand to a sack of Chaux Blanche. This is clearly NOT 2:1, although I have no idea how many buckets of dust there are in a 25kg sack. The French use Multibat for everything, as can be seen by the dosages given on the back of the packet, and all it’s applications. It may be Grey, but it’s virtually identical to Chaux Blanche, so the person who saw it being used for pointing Granite shouldn’t be unduly alarmed. It is 80% Chaux, 20% cement.
Applying the muck with rubber gloves is an excellent way of doing it. You can feel the joints being filled, and there’s almost no wastage. Covering the whole stone lightly allows the mix to be brushed back as it starts to dry. Otherwise a half-covered stone can end up with a white halo where the mortar has dried around it’s edge. This technique doesn’t work too well with granite, but then I’ve seen acid being used to clean this kind of stone. Haven’t tried this myself…
Bon courage a tous!
Andy @ GuillaumeBatiment.fr[/i]17th December 2009 at 04:45 #779013
guillaumebatiment, thanks for the info and as you suggested the air gun is proving to be a very useful tool in preparing for pointing or any stonework.
Interesting about the various limes (or what I had thought were limes) I will have a look at the NHL2 before doing any more.
Is it suitable for the mixed stone of Brittany which where I am is a mixture of slate, sand stone, granite, quartz, and just ordinary stone looking stuff (sorry to be a bit vague but not a geologist) and lots of it looks like it has come from previous buildings.
You sound like you know what you are talking about but didn’t mention any “facts” or pros and cons, about the using of sieved torchis (mud) in the mix which I have been using not only for pointing but also external and internal rendering. Do you think it aids the ‘breathe” of the wall,? but one thing is for sure, it looks great.
On internal rendering (where not seen ie on the gables in the attic space) we are using the sharp sand (0/5 0/4) and the mix 3 sand one chaux and one sieved mud dust.
When we get to rendering where it will be seen and touched we have been advised to reduce to 0/2 sand and then go four sand 1 chaux and one sieved dust.
I would be very interested in your response as we have only done little bits of pointing and rendering up to now but as the new roof is now on we will be getting stuck in inside and also have the outside walls to point in summer.
Only dead fish go with the flow17th December 2009 at 08:28 #779014
I thought I’d throw in a few facts.
Firstly, Chaux Blanche isn’t strictly speaking Chaux (CaO). It’s a cement rich in Lime. [/i]
Could you shed more light on the above bit please?
Raising the standards of swimming pool knowledge and technology.17th December 2009 at 08:37 #779015
w650ParticipantJoined: 24 Jul 2009Location: Deux SevresTotal posts: 968
I must say I do admire the patience and tenacity many of you have shown. I don’t think I would have the stamina to repoint some of the large old barns which many of you have done…….17th December 2009 at 15:53 #779016
Teapot, you’ve done well. These are excellent sources of information, and well worth a read. I must confess to never having read them myself, previously. I was trained by the Compagnons de France, at a time when I was catching the gist, rather than the precise details of what they were telling me, so it’s interesting to see these articles.
The thing that stands out is that St.Astier is a very highly regarded, and for me, a local product. It’s been a couiple of years since I moved away from the white-out mix of Chaux Blanche Hydaulique NHL3,5. This is horrible stuff, and quite an odd liantto use, being neither natural (the implication being that it breaths, nor sympathetic in the way it conceals the natural colour of the aggregate/sand being used. The St.Astier natural hydaulic lime is worth trying, just to see the difference. Their website touches on the importance of purity below:
Limestone and argillaceous limestone that contains silica will also contain sulphates, alumina, iron, magnesium, manganese, potassium and other compounds. Burning the limestone at temperatures above 800oC will combine the above components with the calcium carbonate forming calcium silicates, aluminates and ferrites. The ideal result would be to obtain a product containing the required value of combined silica with the lowest possible presence of potentially damaging other components such as tricalcium aluminate (C3A) and soluble sulphates.
Tricalcium aluminate starts occurring when materials are burned at 900oC and increases at 1,000oC and over. The highest values are found in ordinary cement (sometimes over 10%). Obviously the lower the amount of alumina and sulphates contained in the raw material, the better the final product quality. St. Astier deposits are exceptionally low in alumina and in sulphates, the resulting products are therefore virtually free of these components.
Ordinary cement mortars and mortars made with lime where cement has been added are sure to contain high quantity of tricalcium aluminate which in contact with suplhates and water can produce sulphate attack starting with efflorescence and progressing to damaging joints, bricks and stone. The BS 5628 warns about this but does not indicate that a simple solution could be the use of a pure NHL mortar.
High presence of gypsum is also to be avoided. Its sulphate content can be disastrous.
I think it fair to say that I have overstated the levels of additives used in “ordinary” Chaux Blanche Hydraulic, as it appears to be strictly controlled by the Normes Francaises. However, St.Astier don’t seem too impressed with these guidelines, and I have read that even small amounts of cement in a Lime mix can radically alter it’s characteristics. My gut feeling is that these Lime/Cement cocktails are far too hard, and have seriously impaired breathability. Being in a Limestone region, this is a serious issue, so it is best to look for NHL2, or make your own. If you’ve got time on your side, why use it at all, just stick to Aerienne with a dash of Hydraulic on external aspects battered by the prevailing winds.
Regards, Andy.17th December 2009 at 23:16 #779017
I did my training at the lime centre in the new forest and the owner Bob was a strong advocate of St Astier over others. From the BS certs to the Norms in France I did ot believe that cement was added as that would form a gauge mix which is neither natural or strong in use.
It is interesting (well to me) that La Farge UK admit adding gypsum to their cement.
For me, I stick with the pure and good mixed grades of sand.
When the weather improves I have a church to re-point in East London.
Raising the standards of swimming pool knowledge and technology.17th December 2009 at 23:23 #779018
Andy you didn’t mention anything about me putting the sieved torchis dust in the mix. have you got any opinions or do’s and dont’s about it?
We have saved all of the torchis (french cobb) from one wall that needed replacing and we save all the mud from when we have had to make new openings in the meter thick walls. We just sieve it through a garden sieve and use the dust in the mix. Al of the pebbles get chucked back in as fill when rebuilding the stone walls of building new ones.
The colour when dry is absolutely perfect and blends perfectly with whats there and around.
Only dead fish go with the flow18th December 2009 at 07:54 #779020
A useful source of information:
Raising the standards of swimming pool knowledge and technology.18th December 2009 at 14:57 #779021
I found the first link alarming. What if our cheap Hydraulic Lime has low-level traces of cement etc to aid setting times? According to this, the characteristics of the resulting mortars will be seriously altered. I think we knew that already. Specifically though, what do we do with MultiBat (lafarge). This is 80% Hydaulic Lime, 20% Cement, I believe. The Smeaton project found that all mixes with less than 25% cement failed.
Have I misunderstood this?
I enjoyed reading the second of Teapot’s two links, because it is SO relevant to the everyday practices here.
Bentley asks the effects of re-using old cob in a fresh mix. Although I don’t know the answer, it doesn’t sound right to me. I’ve only demolished cob walls before, and the dirt was dusty, and full of ancient vegetable matter i.e straw, several hundred years old. This has no place in a mortar mix at all. I’d start from scratch, using fresh straw or chanvre (better still, and widely available in sacks), local earth and Lime putty. I’ve seen this done where the shrinkage has been extreme, so with the slow setting time, I’d avoid doing this anywhere with heating. I’d say that the old stuff would be best used on the garden. I’m using my own logic on this, so if anyone has a difference of opinion, I’d be interested to hear it.
Andy.18th December 2009 at 20:01 #779022
No your on the money Andy, it is very important to understand that they are talking mostly about Non hydraulic lime with additions, remember that sets by absorbing Co2 and we tend to use the dry bagged Hydraulic lime which sets with water.
There is stacks of good info to back up the training and i for one am always learning.
Raising the standards of swimming pool knowledge and technology.18th December 2009 at 23:01 #779023
We only use the “sieved dust” from the torchis walls (and we sieve all the stuff that comes out of the walls where we make new openings) All the other stuff like pebbles, straw, sunflower seeds corn ears animal bones and walnuts?, goes back in as in-fill when rebuilding the thick old stone walls.
The stuff we have done so far looks good and feels very solid, and as I said it is 3 sharp sand one lime(chaux) one sieved dust. WE are pointing and rendering with the same mix. Here is a photo of the wall I rendered that goes into next doors garden, And the wall that Mrs Bentley built that has yet to be pointed.
I am not at home at the moment so cant tell you the name and number of the chaux I am using but I will try some NHL2 and see what happens
Only dead fish go with the flow