It is a rare and a beautiful sight to watch traditional lime kilns — surprisingly still surviving today amid the din of machines and urbanisation. Ashok Kumar visits Dambala in Gadag district and learns a thing or two about lime kilns.
While strolling around Dambala village in North Karnataka’s Gadag district, I was surprised to spot some dome-shaped structures built of brick and mud mortar. Chandi Saab, a passerby, who could read my face, said “It is a lime kiln (sunnada batti in Kannada) used to produce quick lime by burning limestone”. He was enthusiastic about showcasing his knowledge to me — an urban stranger, and explained further that it is a seasonal activity of the villagers to produce lime for their domestic and agricultural purposes. Farmers use it as a soil improver and locals as a building mortar and whitewash for walls in their domestic needs.
Of course, Chandi had no idea of the science behind lime formation; he gave a broad smile and left the place. The magic behind lime formation is very simple. Limestone, which is rich in calcium carbonate, when heated around 1000°C in lime kilns, turns into calcium oxide or quicklime. This process is called calcination of limestone.
It is true that lime has been known from the earliest times, and early civilisations used it in building mortar and also as a stabiliser in mud renders and floors. Lime, when added to soil, neutralises its acidic nature and improves the structure of heavy clay soil. Normally, villagers find that it is easy to operate such small kilns and, moreover, it is less expensive for them because limestone is collected from the nearby farmlands and mounds. In coastal belts, oyster (coral and shells) which is available abundantly on sea shores and river banks is burnt to produce quicklime.
The kilns at Dambala are about seven feet in height and three-four feet in diameter. Two to three stones are piled over the other to facilitate a loading platform. There is a central opening, running from top to bottom, and is about one-and-a-half foot in diameter. The locals crush limestone, often by hand, into small pieces of one to two inches in size and pour them into the kiln in alternating layers of limestone and filler materials at the top.
Fillers like charcoal, firewood, cereal straw or corn husk serve as the fuel to burn limestone. Once the loading is completed, the kiln is kindled at the bottom opening, and the fire gradually spreads upwards. When burnt, the lime is cooled and drawn off at the base opening. Fine coal ash is dropped out and is rejected with riddling and lime lumps are collected, but it is not the end of the process.
In order to turn quicklime into a stable and usable product, water needs to be added. When slaked by adding water, quicklime granules turn into hydrated lime, which, if left for some time, absorbs carbon dioxide from the air and the granules bloom like petals releasing heat simultaneously. These lumps are then disintegrated to a fine powder or paste. Depending on the amount of water used, the final product would have different consistencies - however it has the tendency to get hardened back - a neat life cycle! The final paste called slaked lime is an important basic material which can be used in mortar coatings and many other ways.
It is a rare and a beautiful sight to watch such locally operated lime kilns — surprisingly still survive today amid the din of machines and urbanisation.