Pointing a stone wall

A well pointed wall is dry, naturally well insulated, and provides protection against the insects and small animals that will otherwise enter your house through the walls. Old unpointed walls can look nice and rustic, but that doesn't make them funny to live with when you have an invasion of flies éand mice in the house and a heating bill twice as high as it should be.

Old stone walls are also dusty and grimy, and impossible to keep clear of cobwebs etc. So I assume that you will at some point want to tackle the task of pointing them.

Specific techniques will vary according to your location since the type of stone available locally determines the building process used. The broad principles will always be the same however.

The first time I pointed a wall, I carefully researched on the internet and in books, and learned that I should remove all visible stones less than about six centimetres across, and also that the final result would look better if, where two large stones touched each other, I created a groove.

Interesting and rather time consuming, but having watched the mason at work I am now taking a more free and easy (and hopefully traditional) approach - if a stone is small and loose it comes out, otherwise it stays. And no effort to carve grooves between large rocks, which is frankly a complete waste of time and effort, and has no visible effect on the finished product.

I have assumed that the wall to be pointed is structurally sound. If it is not, you will need a mason to repair it before you start. Underpinning and subsidence are beyond my knowledge and in any case are rarely tasks to be tackled by even the most enthusiastic amateur.

It is worth remembering that lime should be used rather than cement for all jointing type work, be it floor tiles or the stonework of the walls of the house. There are several reasons for this, including (in no particular order):

• The manufacture of cement is very environmentally unfriendly
• Lime can breathe better than cement so is much better for the building, but will still prevent rain and water entering the building
• Lime doesn't crack or shrink in the way that cement does, and will 'automatically' fill any little cracks that do appear, so lasts better
• Cement is very hard and extremely difficult to remove from old rocks and tiles, hence the next time these are worked on they will probably need replacing rather than simply cleaning, but if lime has been used it can be removed quite easily
• A cement mix will tend to be harder than the tiles and stones, so these can crack if any slight movement of the structure takes place. A lime mix is softer that the tiles and rocks so will not cause this problem.

You can see that I am not a big fan of cement. To be fair to cement, the Renocal I refer to below is mostly made from lime but does contain a small amount of white cement. It is quite common for a small amount of cement to be added to lime to give it a bit more strength. Never grey cement on a wall that will be visible, always white cement.

Preparing the wall

First you will need to remove any existing pointing or render. This is best done with a pneumatic hammer and an air compressor which is approximately 50 times faster and easier than doing the job manually, and doesn't leave you with terrible wrist problems. The hammer and air compressor can be hired or bought.

Next, your stone wall will need cleaning. Even if the wall looks clean you should do this, otherwise you will be pointing onto a dusty surface. There are two main methods available to clean a stone wall - sandblasting and high pressure washing.

Sandblasting is very effective, but also time consuming and dirty, requiring a mask and protective gear to be worn because of the large amounts of dust and sand flying around. It is a very good way of removing decades and centuries of grime from the surface of the rock. You will need an air compressor and a sand-blasting attachment, and some 'sand blasting sand' - your building suppplier will understand if you ask for 'sable pour faire le sablage'.

Sandblasting has the other advantage that it can be used indoors where high-pressure water washing may be impractical.

Pressure washing is called Karcher in France, after the company that makes the pressure washers (like hoovering in the UK) so my lengthy efforts in French to discuss 'cleaning with water at high pressure' were met with bewilderment until the work Karcher cropped up.

You will need a 'proper' pressure washer that delivers a copious stream of water. These cost a few hundred euros or can be hired. Do not try and use a small pressure washer designed for giving the terrace a quick clean but can only deliver a 'needle' of high pressure water.

Pressure washing is more or less a fun job, albeit wet and dirty. Start at the top of the wall, and wash from quite close up at high pressure. If your walls are held together with clay, as many are, lots of this will flow down the walls, and you will be concerned that you are washing the wall away. You are not, unless you get completely carried away, but show a bit of rstraint when necessary!.

Ideally ou want a 3-4 centimetre depth of join around the stones, ready for pointing, but this will vary a lot. Small stones will fall out - no problem, they were infill not structural.

I have heard that regional differences in house structure may affect the approach you take, and that this method can cause excessive water damage to a wall and other damage.  have seen t used many times but if you are in any doubt or about your own house construction get expert advice!

After the first pass of pressure washing close up, go over the wall again at a greater distance. This will wash the residual dirt generated by the pressure washing off the wall without creating more, and leave your wall ready for pointing.

Pointing a Stone Wall - Method

(this method will vary with area and department)

Ingredients

• 50 litres of sand (buckets are just over 10 litres, often with levels marked on the inside / wheelbarrows are usually 60 litres). If you are using just one colour of sand it is easiest to measure 50 litres into a wheelbarrow, see how much that looks like, then simply use that amount for each subsequent load â much faster than filling buckets). I am using two thirds yellow sand and one third grey building sand, to match the local Lot-et-Garonne 'touch of yellow' appearance. You will need to determine the colours for your department, from a mason or your builders merchant.
• Half a 35 kg sac of Renocal - this is white lime, with a bit of white cement and some other additives, to help with breathing, water repellents and so on, all premixed. Other companies make similar products if Renocal is not available in your local builders merchant.
• 11 - 13 litres of water. The Renocal recommends 10 litres, or 'according to consistency required'. The exact amount depends partly if your sand has been in the rain for the last few weeks, of course - after our sand had been sitting in the barn for a couple of weeks drying out I was using at least 13 litres of water.
• As for total quantities to buy, I do about four square metres with one batch. So for every 50 square metres of wall I will use about 6 sacs of lime, and 600 litres of sand, just over half a cubic metre.

Method:

• Give the clean wall a good spray with water before starting the pointing, the day before and also just before starting work, to avod the mortar drying too quickly and shrinking from the stone. Avoid pointing either in hot direct sunshine or in freezing conditions, for similar reasons.
• Add the water, then the sand, then the lime (Renocal) to the cement mixer, and mix for a few minutes.
• This will give the perfect mix. It will stick to the back of your upright trowel for a good few seconds without falling off. The consistency is similar to thick double cream. It should be easy to apply if you are having to push hard to get the mortar into the gaps it is too dry.
• If you mix more than this in one go you will have to work fast in applying it. If you mix very small quantities - for example, if you don't have a cement mixer - you will find it difficult to maintain a consistent colour from one batch to the next, and you will spend half your time measuring quantities.
• Apply to the wall with a (builders) trowel, ensuring all the gaps are well filled. Apply too much, not too little. Don't worry much about appearance at this stage. This amount will take an hour or more to apply. Don't worry that you are covering up some of the little stones completely. If you practice you will find that you can 'flick' the mix off the back of the trowel and onto the wall, like a real mason, but this is not crucial to the result.
• When the mortar has started to harden, which usually takes three or four hours, use a 'not too hard' wire brush to remove any excess mortar. This is the fun bit, when a beautiful stone wall appears like magic.
• You shouldn't be able to see the brush marks when you have finished. You will know immediately if you are getting it right. Generally speaking, the stone should not protrude significantly from the mortar, although that exposes more stone. Look at other houses before starting, to get an idea.
• Sit back and wait. The mortar will take a few days to dry to its proper colour, while you panic about whether you have got it right.

You now have a well insulated, weather proof, insect proof and environmentally friendly wall. Time taken - about eight square metres of wall a day seems right for me, including brushing, mixing and so on. You could take it easy and do four; you could work harder, miss lunch, and do twelve square metres in a day.

The more batches you do in a day the more complicated it gets because you have a mix of mortar going hard in the cement mixer, while the pointing you have already done also needs brushing, and you want to stop for a coffee.

Note also that the drying time affects the final colour of the pointing, as does any damp in the walls. The faster the mortar dries, the lighter it will tend to be as the lime moves to the surface more when the mortar dries quickly, so if you start pointing your wall in February then finish it in June you will probably have a colour mismatch.

It is perhps impossible to end up with a completely consistent colour over a very large area - certainly our mason hasn't - but you can get very close.