Homes and gardens

COB, BAMBOO, WATTLE AND DAUB

Bamboo and mud make for a strong, durable combination.   | Photo Credit: Special Arrangement

Let us take a quick quiz.

What are the building materials employed during the early days of human settlements? Mud, wood, stone and bamboo.

What could be the most ancient design approach still in use today? Mud architecture.

Which material offers the most sustainable future? Bamboo. Which construction techniques are the easiest to learn? Mud and bamboo.

In these days of cement and steel, the two celebrated construction materials dominating construction all over the world, this quiz may sound sceptical. Contributing to around 15% of direct Green House Gas emissions, cement and steel are not the heroes of world of construction, but the villains of world destruction. Strange but true.

In 50 years, the construction industry in India saw a paradigm shift from its 5,000 years of history. Now with climate change and relatable crisis like corona pandemic, it’s time for a game changer. It’s time to consider mud and bamboo architecture more seriously.

Expertise counts while on the job.

Expertise counts while on the job.   | Photo Credit: Special Arrangement

Mud or soil is not very durable if used directly as was done in the past for they shrink, crack and erode in rain. With additives such as rice husk, stone pebbles, coconut coir, fibrous grass, sticky jaggery, animal hair, durable grass, slaked lime, sieved sand, egg yolk, and puzzolana cement, mud can be stabilised to reduce its shrinkage and cracking. Adequate proportions of clay, silt and gravel ensure the load bearing mix, to be ensured by lab tests or studies, increase surface integrity to make it non-erodible. Pre-mixed one or two days earlier, mud also gets the sticky qualities much needed for molecular bonding.

Once ready, the mud mix can be rolled into balls with both hands together to be directly placed to raise the wall. The balls or cobs need to be pressed dense and then tightly placed one above the other, until different balls virtually become homogenous. Continuous width check has to be ensured and periodically, the edges have to be cut to level to take away the bulging mud. Minor variations in wall thickness happen in cob wall, considered to be the real beauty of the cob construction.

How the coating is done.

How the coating is done.   | Photo Credit: Special Arrangement

Cob wall is ideally a slow construction method, so we should not build fast up to sill or lintel unlike in a cement block wall filling in RCC frame construction. Being slow, it demands more patience, akin to a meditative process. Beneficially, being slow and steady makes it strong and durable unlike the cement block wall which is weak and short lived, on a comparative note.

Wattle and daub is a western coinage but in Indian vernacular traditions it has varied regional words, primarily meaning mat and mud. Simply saying, this age-old idea is the pre-cursor to modern RCC, concrete reinforced with steel inside. In wattle and daub, mud replaces concrete and bamboo replaces steel. In place of bamboo, other local variants including thin branches of highly fibrous plants or woven mats of durable grass can be tried, but bamboo is best suited.

Spacing of split bamboo can vary for different walls types, but should not be more than 6 inches. More recent innovations have been attaching chicken mesh or grass mats over the frame to provide additional dimensional stability to the wall. Water- and termite-proofing the wall is very important which can be achieved by integrally adding lime or applying surface coats. Treated bamboo is preferred, yet is not a must if it would be completely embedded inside the stabilised mud wall. No rusting metal, bio-degradable component and decomposing ingredients that can create a void should be used in a wattle and daub wall.

Columnar support if provided by bamboo and mud roof supported over split bamboo over bamboo mat completes the picture of a bamboo and mud architecture. In case of all material and labour being local, this would have the least of embodied energy, minimised indoor heat gain, aesthetics that calms the mind, reduced capital costs, possibly lowered construction budget and all of this would return to earth, leaving hardly any debris for landfills. Of course, there could be certain limitations in mud bamboo architecture being applicable to all building types across all sites, yet it has far more applicability than being considered now.

Consistent research and development efforts by institutions such as IISc., Auroville, Mrinmayee, Hunnarshala, Costford, CGBMT, INBAR, Thannal, and National Bamboo Mission, varied state bamboo development corporations and many others have led to a resurgent interest in mud and bamboo architecture. Complimentary consultancy support by private architects and engineers have further promoted them, with the major bottleneck lying now only in shortage of construction teams and contractors.

It is a myth that mud and bamboo architecture is only for the rich, with the consultants and builders being unaffordable by the middle class. Low and high costs exist everywhere including in the three basic needs of food, fabric and shelter, so even the normal conventional house construction sector has it. Hence, the misnomer that alternatives are costly needs to be de-mystified. Like every emerging idea, mud architecture has also been subject to style, site location, skill sets, supply chain, service provider and many such criteria, leading the buildings to cost less, medium or more.

By itself, this ancient design and build approach is not boutique, elitist or only for the rich. The owners can choose mud architecture for frugality, finesse or even for fashion. The choice is ours.

(The author is an architect working on eco-friendly designs and can be contacted at varanashi@gmail.com)

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Printable version | Oct 28, 2020 2:41:56 PM | https://www.thehindu.com/life-and-style/homes-and-gardens/cob-bamboo-wattle-and-daub/article32582776.ece

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