Monday, 5 April 2021

More lime if you're interested


People who have rediscovered the benefit of lime-based technology developed over thousands of years tend to be annoyingly evangelistic about it. 

I was taught the basics of lime and its uses by people who were taught by the very man who looked into the science of it during the conservation of the West Front of the beautiful Wells cathedral - Professor Baker. I never met him because I never worked at Wells.

Ordinary Cement mortars have been doing damage to limestones for only about 150 years, but the masons who continue to use it see stone conservators as untrained, mystical hippies who get in the way of serious builders and masons that just want the job done as quickly and as inexpensively as the contractor demands. 

In the old days, there were not many conservators who had a grounding in masonry, and they tended to give the others who did a bad name. Ordinary builders would groan when they were mentioned, and the general stereotype was of a woman with a degree in Art History, wearing dungarees and spending two months wielding a toothbrush or scalpel against a square yard of stone. They were seen more as archeologists than anything associated with serious building.

These days you cannot work on an historic building without knowing about lime and lime-based procedures, but only a few years ago, masons who were forced to use lime mortars on important buildings would wait until the conservation officer or architect's back was turned, then put handfuls of white cement into the laboriously mixed real thing, killing it off completely. The biggest obstacle was getting them to understand that mortars are not supposed to be used as glue, and the mortar should never be harder than the stone itself. The science behind it all could wait for them to muster any interest - or stifle any hostility - toward the whole process, just so long as they followed the instructions to the letter.

Of course you have to use ordinary cement in modern construction, but remember that concrete made from lime is nothing new. The very word 'concrete' comes from a reference to Crete, which had large quantities of volcanic ash used by the ancients to make their concrete set, even under sea water. There are concrete supportive pillars beneath the Great Bath here which are as solid as they were 2000 years ago, thanks to the addition of pumice.

There are only a few things you need to understand to get your head around lime. The first is the chemical make-up. A good mortar should have a mineral and chemical composition as close to the natural stone as possible. Over the years it bonds to the stone by replenishing the minerals leeched out of it by weathering, so it protects and strengthens. Lime is highly alkali, so it also neutralises the acids which accumulate on surfaces from a number of sources.

The key is crystallisation.  Sharp sand - or even sharper pumice - sets off a crystallisation process which takes weeks, months and years to develop, so the maturation of lime mortar is not measured in the couple of hours that ordinary cement  takes to chemically set.

The Victorians were entranced by the potential convenience of Ordinary Portland Cement and over a generation all of this ancient knowledge was forgotten. Now when you talk about it, it sounds like magic. 

In a way, it is.

32 comments:

  1. That was interesting. Yes, really. I had heard about pillars that were under water and as strong as when they were first built. You are right, it is magic.( how the hell did they know these things?)

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    1. Ancient wisdom concerning buildings and materials were collated in a book written by a Roman architect called Vitruvius. Even he had a magical outlook on the whole business and it wasn't until Professor Baker turned up that anyone looked into the science of it all. It is a strange mixture of intuition tested by trial and error over a very long period of time. These days, intuition is not enough. You have to prove that something works and explain how it does work.

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    2. They used to say, 'This is how it has always been done and this is how we are going to do it', then the chain was broken. In Vitruvius's day, architects were trained for 21 years before they could practice, and part of the training was music and acoustics.

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  2. When I worked for the Council our office overlooked Norwich Cathedral across the city and four of us used to play a game to pass the time that we were Norman builders on the original construction site and we would invent things that had gone wrong from day to day and imaginery conversations between workmen. Like spires collapsing, walls falling, wrong mix etc. Caz above asked how ever did they know these things. They didn't. It was trial and error and they were learned by making a lot of mistakes on the road to getting things right. My recent studies of the Italian Renaissance also brought up several major disasters in buildings during construction.

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    1. Don't forget that the Italians had their own Dark Age too. There was a gap of at least 1000 years between the the fall of Rome and the Renaissance. Have you read 'The Spire' by William Golding?

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  3. You've sent me off in some very interesting google searches lately. My husband has been reading along as well. We don't know a lot about masonry, but it has been something that has fascinated us for some time. We took a trip to DC to see masonry craftsmen plying their trade. I was a little shocked a few posts back when I read that you felt as if people might see you as an old man who should be retired, but isn't. Mostly because I see you as a craftsman whose expertise is still in demand.

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    1. Covid has fucked everything up for me like it has younger people.

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    2. I'm sorry to hear that. It's hard to know what to say when life just plainly sucks for someone. I'm often at a loss for words over at Northsider's blog too. These are tough times.

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    3. For me it was a perfect storm.

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  4. Interesting. Nineteenth century ancestral relatives of my wife's family had interests in the limestone quarries at Levitt Hagg near Conisborough. It was used for fertiliser as well as building. They made a lot of money of it, none of which passed down to us.

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    1. Same with my family and beer brewed in the East End of London.

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  5. Interesting Tom. Reading Tasker above - we used to spread lime on our land now and again when we farmed how does that fit into the equation?

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    1. If you have acid soil, then I imagine spreading lime would help with the PH balance, but I am not an agricultural advisor for The Archers.

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  6. Interesting- I didn’t know any of that. It is sad that the right way to do things is lost in so many trades. It seems that there is only ever a handful of people who are really knowledgeable and skilled.

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    1. This comment has been removed by the author.

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    2. I deleted my comment because I misunderstood Iris at first. Sorry.

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    3. Not many things die out completely over a couple of generations, only traditions. Science rules over all now, and old wisdom is - quite rightly - questioned.

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  7. The use of lime is fascinating.
    I was working on the house I used to own in South Wales, and it was highly annoying that what was being pushed were pink plaster, cement pointing. Chemical dpcs and silicone waterproofing of outside walls of stone built houses...and they wondered why the damp was locked into a house....

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    1. Welsh builders have a lot in common with Cornish ones, not least English second-home customers.

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    2. Welsh council departments seemed ignorant of matching the age of construction to the method of mending...

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    3. And UPVC window companies made a killing in Cornwall. Cement render pebble-dash is the preferred finish in those parts.

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  8. Baker documenting the science and use of lime was instrumental. Do regulators uphold proper use of lime and safeguard standards for conserving buildings? It would seem you would be on a short list of individuals qualified and approved to work on listed buildings.

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    1. Yes, the restoration and conservation of buildings is very tightly controlled now. I used to be on the approved shortlist, but now the list is quite long. I was one of the first members of the UKIC and a friend of mine created the stone side of it. He made up the rules as he went along.

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  9. It is a stunning building. I cannot imagine it being constructed. More magic.

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    1. Some people think that it used to be brightly painted.

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  10. I love Wells Cathedral, don't the swans ring the bell? There is something sublimely timeless in the greenery around the building. The Japanese have Intangible Cultural Heritage, craft is honoured, shame we don't have something similar in this country.

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    1. Yes the swans ring the bell to be fed every morning. A couple of weeks ago someone accidentally drained the moat and the swans were left high and dry. Our idea of a National Living Treasure is Judi Dench.

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    2. I mean at the Bishop's Palace, of course.

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  11. Our neighbours had some sort of lime render put on the side of their Edwardian terrace house ( to help it breathe? ) and I once caught my knuckle on it while putting their bins out for them. It was only a small scrape but it took weeks to fully mend and still used to hurt a bit for ages afterwards.

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    1. Lime render will 'breathe' by letting moisture in and out. Cement render traps it and does not breath. Maybe you had a bit of a lime burn, but if you washed it after the graze that should not have happened. It was probably an infection. Lime is a powerful anti-septic.

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  12. This is fascinating. You have so much knowledge and wisdom.

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