Ever wondered why a lot of Delhi’s medieval monuments—the ones with plastered exteriors, not stone—have that blackened look about them?
With Delhi’s humid climate (particularly the fact that several months of the year are taken up by the monsoon) means that there’s a fair amount of rainwater falling on buildings. And rainwater, if preventive measures are not taken, can seep into buildings and eventually cause structural damage. To avoid this, medieval masons used ‘organic mortar’ to construct: the mortar, besides containing more ‘usual’ building materials like rubble or limestone, also contained organic ingredients: cow dung, yoghurt, urad dal (black lentils), fenugreek, and wood apple pulp. The organic nature of the mortar made it breathable, thus preventing waterlogging and prolonging the life of the building.
Organic mortar, however, does have a downside: just because it’s organic, it is prone to organic growth, and over the course of just a year can begin to acquire a coat of black, thanks to algae growing on the surface. Hardly surprising, then, that over centuries, some buildings become so black that the colour almost seems planned.
Nowadays, a lot of conservation work continues to use traditional techniques, including the use of organic mortar—which means that even recently-restored buildings can have blackened surfaces soon after work’s been done on them. Rest assured: it’s all for the best.
The use of organic mortar isn’t restricted to Delhi; organic mortars were used, though sometimes with regional differences in the ingredients, in other parts of India as well. For example, in Hyderabad’s Golconda Fort, the organic mortar included eggs and chana dal (Bengal gram).