I know I have been a little obsessed with sand of late but, as an integral part of traditional lime mortar and render, it is important stuff.
I have written about buying it in France and I have offered my unofficial advice about reusing it in order to keep your building materials as authentic as you can.
Because, as we can all agree, there are good restoration jobs and bad ones, the latter being where you can clearly see where new work has been done.
Sometimes, a clash is unavoidable but a job will look much better if you can successfully imitate the old.
Which brings us to the following problem: you want to repair an old wall which was made centuries ago with lime mortar, and you want to get as close as you can to the original colour.
In a way, phrasing it like this is ingenuous. What you see on your wall has weathered and aged. Once, the mortar would have been a different colour and you have to decide whether to go for what is or what was.
Either way, it is not that simple because mortar dries and changes hue as it does so. You can get it just right and slap it on but you will not know the tone of it until hours, days or even weeks later.
Even then, it is likely to mature further. I say this as a warning not to be too perfectionist. The aim has to be to get it looking as good as can be.
Ad
So there I was, standing in front of my neighbour’s façade discussing with him how we might get the right shade of lime mortar. The more we looked at the wall, the more we realised how many subtly different tints it had already.
Nick adds a touch of turmeric…Nick Inman
We agreed that we did not want the new mortar to be too pale. We were going for a nice ochre colour that would not leap out and offend the eye.
We decided we would experiment and this is when it occurred to me how tricky the task was going to be. In the olden days they would have taken a load of local lime mortar and mixed it with river sand without worrying about exactly what it was going to look like.
Not-so-mellow yellow was the resultNick Inman
The right sand is certainly important, but it is no longer legal to go dredging in the river. That meant we had to try other options. First we went shopping for different batches of modern sand; then we made various samples using grey and white lime; and finally we mixed a little cement in to see if that would help.
While we were doing that we also explored the shelves of our local DIY shop for proprietary mortar dyes: they need to be used sparingly but even so they did not produce a natural effect. I even tried mixing up a batch of mortar with a splash of turmeric in it, but it looked garishly yellow.
We used an egg box and yogurt cartons for the different batches, clearly marked so we would not get confused. We allowed the samples to dry for a good week or two before carrying them over to the wall to see if we were anywhere close.
In the end we struck a formula using a bucketful of one of the sands we had bought, which was naturally a little ochre coloured, and three-quarters/one-quarter bucketfuls of lime and cement.
We filled holes and plastered a large area of the façade with this mixture and it did not look half bad. Where we joined the new mortar with the old, we made sure to fudge any sharp lines.
As our mortar dried, it changed colour of course, but the repairs are not shocking. Gradually, the new will blend with the old. I have no doubt.
I also have no doubt that few people will consciously notice our impostor handiwork.
