Are ‘Natural’ and ‘Sustainable’ the Same?

Since forever, burnt clay bricks have been promoted as being natural and therefore the obvious choice for our homes. But we all know the damage they’ve been causing to our health and planet. In India, we produce 250 to 300 billion bricks. Accounting for the most conservative average carbon footprint per burnt clay brick of around 0.5 kg CO2, brick kilns alone are responsible for 125 to 150 million tons of CO2 emissions – about 4-5% of India’s annual carbon emissions. But you know what? That’s not the only issue. With coal becoming super expensive, brick kilns have started using all kinds of cheaper solid fuels which release toxic gases. The beautiful, silky smooth, natural soils that are used to make red bricks are also the soils needed to produce food. And when arable land becomes inarable, forests are chopped down for agriculture. We all know the problems with not having forests.

A similar trend has emerged in the recent past for an equally older material – lime. No doubt one of the oldest binding materials, lime has gone through several millennia of transformations before it became the modern-day Portland cement. While its history is quite fascinating, the environmental impact of lime was quite evident even when it was the primary building material. Today, kilns have evolved and are more energy efficient, and less polluting, but have an acute climate impact, nevertheless. Building limes are produced from naturally occurring limestone. The quarried limestone is burned at around 900-1000°C in a kiln using coal, which releases large amounts of carbon dioxide. Further, carbon dioxide also gets released as a product of the chemical reaction in which limestone turns into quicklime. In total, approximately 900 kg of carbon dioxide is emitted to produce 1 tonne of building lime. ‘Artificial’ Portland cements have a much lower carbon footprint these days. And then there is the problem of poor strength of lime. Applications are limited and it is just a general hassle to work with.