Concrete is the most consumed resource on the planet, after water. Cement, the key ingredient in concrete, has shaped much of our built environment – our houses, buildings, bridges, roads and dams. However, its carbon footprint is massive. The cement industry is one of the primary producers of the green house gas CO2 and accounts for about 8% of the world’s CO2 emissions, according to think tank Chatham House. Concrete also damages the topsoil, the most fertile layer of the earth rich in microbes. The hard surface of concrete contributes to surface run-off that leads to soil erosion, water pollution and flooding. Concrete and cement production is highly centralized, and also capital and energy intensive. Hence modern construction has become a very expensive activity. Even after construction, maintaining the buildings (heating, cooling, lighting, etc) is very energy intensive. Construction and buildings together account for 39% of the CO2 emissions according to the Global Status Report of 2017 by the UN Environment and the International Energy Agency.
With the growing awareness of the unsustainable nature of construction using concrete, researchers worldwide are working on finding sustainable materials and methods of construction. In this light, let us look at what the traditional knowledge of India has to offer, and more specifically, the significance of cows for sustainable construction.
Our traditional methods are aligned with nature and houses are constructed without disturbing the trees and water bodies in the region. The direction of the wind and natural light are carefully studied in order to reduce the use of air conditioners, heaters and lights. Construction materials are earth-based and locally sourced to avoid transportation costs. Earth-based construction is cost-effective, eco-friendly, energy-efficient and durable. The cost of Earth-based houses are 40% lower compared to conventional houses.
Earth-based building materials – cob and Adobe
The simplest and oldest earth-based building technique is cob, which is an amalgamation of soil (dug for the foundation), clay, cow dung and straw. The proportion depends on the type of soil in the local region. Cob is a great thermal mass, which means that it stores heat energy and releases it very slowly, thus maintaining a constant interior temperature even with large temperature swings outside. It keeps the interior of the building cool in summer and warm in winter. Construction with cob therefore makes the building energy-efficient. Adobe is another earth-based construction technique. Adobe is made from sand, clay, and water, together with fibrous materials like straw and cow dung, which is shaped into bricks using frames and sun-dried.
Adobe making. (Left) Tamil Nadu (Right) Ladakh
Mud houses are structurally very strong: they can withstand severe winds and seismic activity due to the circular design and thick mud plaster. An example of long standing round mud houses in India are the Bhunga in Hodka, Gujarat. The Beehive houses in Harran, Turkey are made of Adobe entirely without wood, and date back to 3000 B.C. The ancient Bantu civilization of Africa also built houses with mud, poles and cow dung. The roundhouses in Chalton, England, UK, built more than 2500 years ago and the Native American people’s settlements in the USA 700 years ago are also examples of lasting mud constructions.
Mud and dung houses that stood the test of time. (Top left) Bhunga houses in Hodka, Gujarat. (Top right) Round houses in Chalton, UK. (Bottom) Beehive houses in Harran, Turkey.
Cow dung as soil stabilizer
Now why is cow dung used in the construction material? Cow dung acts as a good binder and a thermal insulator. The fibers present in cow dung also prevent cracking. Modern scientific studies show that cow dung functions as a soil stabilizer. A soil stabilizer is a material that improves the durability of the soil by increasing its strength and resistance to water. In an investigation on the use of cow dung as a soil stabilizer in the construction of Adobe bricks, bricks with different cow dung – soil ratios were tested for compressive strength, permeability, erosion and cracking. The results showed that the ratio of 1:4 (cow dung: soil) had the highest compressive strength and resistance to erosion. The ratio 1:5 had the highest resistance to water permeability. Furthermore, there was minimum cracking in all the treatments.
In another research study, the effects of cow dung on microstructural changes in Adobe bricks were investigated by the method of X-ray diffraction, thermal gravimetric analyses and scanning electronic microscopy. It was found that cow dung reacts with kaolinite and fine quartz to produce insoluble silicate amine, which glues the isolated soil particles together. Also, it was observed that the significant presence of fibers in cow dung prevents the propagation of cracks in the brick and reinforces the material, leading to a homogeneous Adobe microstructure. There was a significant improvement in the water resistance of the bricks, making Adobe stabilized by cow dung an advantageous building material for wet climates.
A video microscopy image of cow-dung. Natural plant fibres are its major component and they have a rough surface which enhances the adherence between these fibres and the soil in Adobe bricks. This prevents crack propagation and reinforces the material, thus improving its mechanical strength.
(Source: Millogo et al. 2016)
Cow urine is also added into the mud while making a cob/adobe mix as it enhances the property of mud and enables good curing of the soil. Cow urine is also a potent medicine and is used for treating different ailments in Ayurveda, the Indian system of health.
Plasters are like the skin of a house: protection from temperature and moisture. The skin protects the house against heat, rains, winds and erosion. Mud plaster, mud and lime plaster and Vedic plaster are some examples. In a mud plaster, the components of mud themselves act as binder (fine) and aggregate (coarse): the fine clay in mud acts as the binder and the coarse sand acts as the aggregate. Fibers like rice husk are added to reduce crack propagation. Cow dung is added for better binding and water resistance. It also acts as a thermal insulation. In the mud and lime plaster, lime, along with clay in mud acts as the binder and sand (in mud) is the aggregate. Lime helps to keep termites away. Cow urine is also added for curing which increases strength. Vedic plaster is a gypsum based cow dung plaster along with some minor additives. Gypsum is used as a heat resistant, moisture preserving, sound absorbing and fire proofing material. It is naturally occurring and non-toxic and was used in the construction of the ancient pyramids of Egypt.
When it comes to floor plastering, cow dung is traditionally used. Cow dung contains 3-5 crores of useful microbes. It has anti-fungal properties and also repels insects. A mud and cow dung paste is applied to floors and also serves to disinfect the floor. Cow urine is also used as an additive for plastering floors owing to its anti-fungal property. It prevents the growth of harmful fungi on the walls and floors. Cow urine is also an extremely good sealant for earthen floors. Cow urine is used for sealing the top surface of the finish, preventing crack formation.
Traditional paste of cow dung and mud applied to floors.
Modern paints contain volatile organic compounds (VOCs) which are chemicals inside the paint that are released into the air during the process of painting. Even though the majority of VOCs leave the paint as the wall dries, not all of them do; the paint can release VOCs into the air for years after painting. VOCs are dangerous for health because they are known carcinogens (agents that cause cancer). According to the US Environmental Protection Agency, commonly used paints contain chemicals such as benzene, methylene chloride and others that have been linked to cancer. Therefore, turning to natural plasters is no longer an option; it is a need.
Neuro-cognitive properties and emotional health
The cow dung in the wall and floor plasters also improves mood and reduces depression via inhalation of a bacteria that functions as an anti-depressant. Cow dung is rich in the bacteria Mycobacterium vaccae. The name of this bacterium originates from the Latin word vacca meaning cow, since it was first cultured from cow dung in Austria. which is a non-pathogenic species that lives naturally in soil and it is inhaled when people spend time outdoors, especially in the vicinity of plants and trees. In 2007, neuroscientist Christopher Lowry and his research group at the University of Bristol, UK, discovered that the bacteria activated groups of neurons in the mouse brain responsible for producing the neurotransmitter serotonin, which reduces depression and anxiety. Interestingly, the neurons that were activated were also known to be linked to immune response, suggesting an intimate connection between the immune system and emotional health.
Microscopic view of Mycobacterium vaccae, a non-pathogenic species of bacteria found in cow dung. The bacteria was found to activate neurons in the brain responsible for producing serotonin, the neurotransmitter that reduces depression and anxiety. Interestingly, the neurons that were activated were also known to be linked to immune response, suggesting an intimate connection between the immune system and emotional health.
Since ancient times, cows and bullocks have provided the energy required for constructing natural buildings. The native breeds of cows are very strong and robust. Hence, they are excellent cob kneaders. The traditional chakku, or the mortal mixing wheel was also turned by cattle. Mortar mixed by bovine power is said to be of a very superior quality, even when compared to mortars mixed with modern grinding equipment.
Thus, cows play a significant role in natural building. The use of cow products in building materials has been scientifically reasoned and validated by modern research studies. It is time we translate this understanding into action and actively promote cow-based building and living.