How recycling old sand for restoration work looks quintessentially French

On reflection, I knew it was a rude question; but I had to ask it. 

To research my previous article about buying sand in France, I went to talk to a man who makes his living selling different kinds of the stuff. 

We went through the various grades and colours he sold and then I asked: “What if when I demolish a wall, I collect the sand that falls out of it and re-use it to make new mortar?” 

He frowned and – I suppose understandably because he did not want to do himself out of a sale – advised: “I wouldn’t do that. It’s always a good idea to use new sand because it is pure, clean and uniform in particle size and colour.”

Two days later when I put the same question to my favourite expert on old buildings, she was delighted with the idea. 

“Why not,” she said, “although you would have to check before you use it that it doesn't contain soil or other impurities.”

As it happens, I have been re-using crumbled mortar for the past 20 years without any problem. There are at least three good reasons to do this. 

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Recycling sand

One is because it is environmentally friendly. The world is going to run out of construction sand one day at the rate we are going (all that sand in all those deserts is the wrong kind), so it makes sense to recycle what you can. 

Secondly, if you are going to make authentic-looking mortar to suit a period restoration, it helps to use authentic sand. You could say that I fundamentally disagree with the sand merchant. 

For my old farmhouse, I do not want new mortar to look uniform. I want the imperfect nature of the old.

The third reason is that you save a little money and the hassle of fetching the sand or getting it delivered, although I agree this is a marginal incentive because recycling takes work. Re-using old sand is a lot more time-consuming than ordering in a delivery.

For me it is a no-brainer. Why should I drive bags of sand to the local dump when I can still get something from it?

When I work on an old bit of masonry, I have a routine. If the surface at the bottom of the wall is not perfectly flat and sweepable, I put a piece of plastic sheet down to catch whatever falls. When there is enough of the stuff to process it, I gather it up.

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Using mortar to fill holes

The next step is to inspect it visually. Out go any leaves or other organic material. Next, I remove any big lumps of mortar that have not disintegrated into powder. These can be useful for filling holes – waste not, want not. 

Then I decide whether or not it looks like good building sand. If I am not convinced – which happens rarely – I use it to smooth out lumps in my bumpy lawn. 

I am now left with a crude mixture of sand and small stones. If I want a very rough mix, this can be combined immediately with lime (chaux) and put to use. I am told it does not mix well with cement, a modern industrial product, but I have never tried.

For the most part, I need sand of a semi-fine quality, otherwise the mortar is too lumpy to use. So I sieve the rough mixture once or twice until I get the consistency I want, storing sand of different grades (coarse, medium, fine) in separate bins until needed. 

It can be a tedious and time-consuming business recycling, and sometimes I am tempted not to bother, but then I think: the constituents of the mortar are just as much an authentic part of the building as the stones and the bricks. Why discard the old when it can still be put to good purpose?