Lime. Oh lime. So versatile. So useful. But sometimes so difficult to know which kind you’re buying. You may remember my beginners' guide to different kinds of lime I penned last time. Sometimes though, all the CaOs and NHLs in the world won’t help you, because you live in a place that doesn’t regulate too carefully, and your lime turns up in mysterious dog-eared bags which inspire anything but confidence.
In that case you can always do what Gautam Singh in Mumbai did. Cut out the middle man, and make it yourself. He shared his process in our members' only Facebook Group last week, and I think it's fabulous.
“Unsure and concerned about of the quality of lime we were purchasing, especially for some tadelakt work, we made a small kiln to make our own lime,” says Gautam, who is still battling on with plaster work over there in Mumbai. I’ve got to hand it to him, he’s not a quitter:)
“It's specifically for tadelakt,” he says, and “I’m happy to say it works, and wasn’t too complicated or time consuming either.” Oh...music to my ears!
How did they create their own quick lime?
First Gautam and his friends built the kiln out of cob (see above). Next, he collected a bunch of oyster and clam shells from seafood sellers. You don't crush the shells, they are left whole so they are easy to identify post burning, because the entire burned shell will be converted into Calcium Oxide or pure lime.
“Research stated the shells needed to be fired between 800-1200℃. Any less and it wouldn't have the reaction that turns it into lime, and any more would melt the shells," he informed us.
I asked him how he measured the temperature. "Figuring out the temperature was tricky at first, but luckily a professional potter friend came to the rescue and we used a thermocouple to measure the temperature for the first two trials. After that it became easier because then I knew it took between 40-60 mins to achieve that 800-1200 degrees required for my kiln."
In the beginning Gautam thought he'd failed. But in fact it's a good example of how things are sometimes not what they appear. "After our first firing attempt, we went through the burnt matter, extracted all the shells and put them in a pot. Then we tried adding water. But there was no reaction!”
Our pioneer thought perhaps he hadn’t fired the shells at a high enough temperature. He prepared his kiln for a second attempt. It was then he chanced upon a golden nugget of online information advising the use of warm water (not cold) to slake the burnt shells. The Mumbai team decided to try it.
“So we used the same shells, added warm water and voila! It started boiling and reacting violently,” he says.
To test the lime, the team made a limecrete brick out of the slaked lime and crushed bricks. They allowed it to cure completely.
“That brick has been lying completely submerged in a bucket of water for over two months now. It's hard as a rock, completely unaffected by the water,” says Gautam.
Fantastic! The Mumbai crew have now kilned more batches seashells and are slaking them for a nice long time to create the optimum lime putty. They added jaggery and haritaki seeds (terminalia chebula) to the mix, because this lime will be used for a special type of Indian tadelakt known as araish.
As Gautam explains, "Traditionally in India, sand was rarely used with lime...Crushed bricks (essentially burnt mud including a certain amount of clay) are used with lime for mortars, plasters, etc with no need of sand whatsoever. This includes the Taj Mahal and various other ancient structures still standing.”
I also used crushed bricks in a limecrete in Turkey, and can attest that it creates a wonderful crete. This is because crushed bricks are a pozzolan (a burned material such as ash) that creates a reaction which hardens the lime. But I'll stop right there, because I’m delving deeper into the wonderful world of Indian lime plaster next time.
For those wanting to contact Gautam and learn more about his project, MudWorks is just beginning.
Making Lime from Scratch - An Overview
1. Build a kiln from cob, or some other material that can stand 1000 degrees heat.
2. Collect some oyster/clam shells, or limestone (see video below).
3. Light a fire in your kiln and add your limestone/shells. Get the temperature up to between 800 and 1200 degrees.
4. Extract the shells (if using) and put them in a vat.
5. Put on protective clothing (mask, goggles, gloves, onesie etc)
6. Add warm water to the burned shells and watch the mixture bubble and throth. Be careful. Lime is caustic and can burn.
7. The longer you leave that substance slaking (submerged in plenty of water), the better quality lime you get.
Mr Primitive Survival has a video about doing all this with limestone, which is also rather funky.
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