Sindhu Bhaskar builds an earth oven outside her family’s natural ‘earthbag’ home in Thiruvannamalai. Photo: Sindhu Bhaskar
Though over one-third of the world’s population still lives in homes made with mud, somewhere in the mid-20th century, this trend took a sharp decline. A recent survey conducted by scientists from India and The Netherlands ascertained that cement’s popularity and availability were the main reason. Moreover, it noted that it is not so much a matter of quality, as it was a matter of “societal image” that is the key barrier to accepting earth as a building material.
Despite the odds against it, mud may yet make a comeback. India’s housing shortage and the critical need to reduce carbon emissions are prompting many to consider a revival. Cement manufacturing accounts for 8% of carbon dioxide emissions and 2-3% of the global energy supply. But it’s so widely and readily available – India is the second-largest producer – that cement and concrete have come to be the preferred material for all kinds of construction, including housing. Meanwhile, the Indian government aims to achieve housing for all by 2022. This seems a distant goal now, and it doesn’t help that the cost of cement and concrete has risen and is likely to keep increasing with fuel and transport costs.
But the recent survey published in Construction and Building Materials exposed how deeply the idea of poverty is entrenched with earthen housing. Notably, ‘kutcha’ houses (made of unburnt bricks, bamboo, mud, grass, reeds, thatch, etc.) are treated as an official indicator of deprivation in the formulation of the poverty line. For earth to be considered a practical solution to the current housing shortage, the authors emphasised the role of NGOs in promoting construction using local materials and providing consultancy and knowledge for safe construction with the earth.
Sindhu Bhaskar is part of one such organisation. Thiruvannamalai-based Thannal Mud Homes Trust is a natural building awareness group founded by Bhaskar and her architect husband Biju in 2011.
Though Bhaskar is deeply involved in all of Thannal’s activities, she is most known among the community to be a virtuoso with plasters. Plasters can be thought of as the skin of the building. They are the key to protecting the structure from harsh environmental conditions like heat and moisture. Additionally, they add aesthetic value to mud buildings – this is significant considering the role of ‘image’ in the public’s resistance to mud homes.
After years worth of trial-and-error, Bhaskar and her team have successfully developed and refined five different recipes for plasters. These use different proportions of mud, lime, and other natural materials such as cow dung, egg whites, aloe vera, and fibres.
Bhaskar stressed how their work is based on age-old ideas. For example, cow dung has been used since ancient times as an insecticide and a waterproofing agent; similarly, cashew nutshell extract has been used as termite-proof for wooden door frames and is an excellent antioxidant. She is skeptical about mixing mud with cement.
The thoughtless addition of cement to natural buildings is an especially sore point with Thirumalini Selvaraj, a civil engineer at VIT University, well known for her work in restoring heritage structures. “What happens is this,” she said: “lime is a low-strength material compared to cement, but has high durability. If you take a lime building and replace it with cement, it is incompatible. Cracks will appear.”
When restoring old buildings, Selvaraj has one mantra – know the properties of the materials and the technologies that were used to build them. This is where her specialty lies – in identifying materials used, finding its properties, and understanding how it was processed. Based on this information, she looks for locally available materials that are most suited to restore the original structure. “Respect the original architect,” she stressed.
Selvaraj has worked on restoration projects of several famous monuments including Charminar in Hyderabad, Vadakkumnathan Temple in Thrissur, and the Padmanabhapuram Palace in Kanyakumari. “With each project I do, there are many surprises. The information we get from studying these structures gives solutions for modern problems,” she said.
One solution that Selvaraj repeatedly encounters in her job is lime. Lime is derived from limestone or calcium carbonate. After burning and slaking, it takes the form of calcium hydroxide. This form of lime has been used as a binder in construction for thousands of years around the world. Lime is a favourite topic for experts in natural building for a variety of reasons. Besides being an effective, breathable, and healthy building material, it is recyclable. Within the structure, lime hardens with time as it sets back to limestone. More importantly, during this process, it performs one other ecologically invaluable service. It absorbs carbon dioxide from the atmosphere.
Selvaraj’s faith in lime was reaffirmed recently while she worked on the restoration project of an 18th century haveli in Udaipur, Rajasthan. “We found that the lime mortars were in great condition, equivalent to modern concrete. The fibres and natural extracts added to it prevented tensile cracks, and carbon capture was happening, too,” she said.
For the haveli project, Selvaraj faced the daunting challenge of deciphering the cocktail of natural extracts used to strengthen the limecrete (similar to concrete, but with lime instead of cement). “We needed a lot of data to accomplish this. Being from south India, I had to visit Rajasthan, monitor the monument, find the sthapati (temple architects) and interview them extensively,” she said. The rest relied on her expertise in various scientific techniques such as scanning electron microscopy, x-ray fluorescence, x-ray diffraction, and Fourier-transform infrared spectroscopy. Eventually, she was able to determine which fermented plant extracts and hemp fibres were used by the original builders of the monument. Further trials in her laboratory helped her figure out the amounts and combinations. Only then could they prepare a compatible substitute material to fix the damages on the structure.
It’s not just for heritage buildings that Selvaraj sees value in natural building materials. “People think that cement is good because it is stronger. This strength may be needed for high-rise buildings but not for low-rise ones,” she says.
At Thannal, Bhaskar and her team are proving that a cement-free natural home is possible and practical – and according to her, anyone can do it. “You don’t have to be a learned man or someone with great dexterity,” says Bhaskar. “Thannal’s aim is to give this back to regular people, to convey to local people that they can build a small home themselves. How can a family live in a place content and comfortable – that is all we are teaching.”
Note: The Wire Science edited this article at 12:15 pm on March 11, 2021, to remove an individual’s identifying information after assessing their request.