BUILDING WITH EARTH
Tucked away deep in the heart of Auroville, the Auroville Earth Institute (AVEI) is an inconspicuous place that has explored offbeat techniques for building construction. It specialises in stabilised earth and ferrocement construction. We had the opportunity to learn some of their techniques at the CSEB Intensive workshop offered by the institute. The workshop was primarily on Compressed Stabilised Earth Blocks (CSEB), lightly touching upon constructing with rammed earth and poured earth, making composite lintels and building arches.
The first two days were dedicated to understanding the theory and technicalities behind working with earth and making CSEB. Taught by Satprem Maini, the director of AVEI, the course covered all relevant requirements for smooth CSEB production starting with its merits, identification of soil, machine parts, production technique and economic feasibility. The next four days revolved around putting what we learnt in theory into practice guided by Mr. Ayyappan, co-director and senior masonry technician.
Entrance to Auroville Earth Institute
We came to realise that the possibilities of building with earth are boundless. So why build with earth?
Think Local! The soil used for the walls is usually taken from the site of construction. This brings down material and transportation costs and the cost of clearing excavated soil. If planned in advance excavated portions of the site can be used as landscape elements, basements, sumps and rainwater collection pits.
The epitome of sustainability. Earth has been used since ancient times for building construction. It is one of the most sustainable building materials. It is biodegradable, has minimal carbon footprint and is incredibly cheap. It takes lesser energy for production than many other building materials.
Minimum skill. The production of CSEB and rammed earth construction does not require skilled labour as needed for the construction of exposed brick walls. It can be learnt and mastered by just about anybody.
Zero plastering. With unique textures and colours, earth walls don’t require any plastering. The stabilisation gained from cement is what makes these walls resilient.
Save on mortar. Using rammed earth requires no mortar and CSEB only requires 1 cm thickness for the mortar joints.
CSEB Manual press
Any construction with earth starts with understanding the characteristics of the soil. Soil is usually a mixture of clay, silt, sand and gravel. Understanding the mix helps in figuring out the composition of the soil and using that to decide the amount of stabiliser required. Deciphering this had us huddled in teams of four, trying out different methods for identification and announcing random numbers as percentages for each component. After having relentlessly tried identifying the soil components for four days, by the end of the course, we could understand the composition by the look and feel of the soil.
CSEB, as the name suggests, are blocks where every 230 litres of sand and soil is stabilised using 5% or 16.67 kg of cement and then compressed using a manual or motorised press. Stabilisation with cement is what gives the blocks strength and resistance to weathering. We toiled at the workshop shovelling sand into wheelbarrows. The first step was dry mixing sand, cement and soil where one would shovel portions of the mixture to the side and the rest of us would mix it with our hands. This was done twice to ensure the components were mixed well. The next step was humid mixing where water was poured on the mixture and the same mixing process as before was repeated. This was done twice as well to ensure it was good mixing. A bit of the soil was then made into a ball and dropped from a height. If it broke into smaller pieces, the moisture content was perfect. If the ball breaks apart as powder then it requires more water. After the drop test, the best mix is then scooped into the pressing mould. The press consists of a lever that has to be pulled down. After the mould is locked, the lever is pressed down to the bottom until the lid of the mould automatically clicks open. Summoning all our strength, all the participants of the course tried our hand at pulling the lever. It is difficult but possible for one person to operate the lever, however, the last bit requires a team of two to crack open the lid. A pocket penetrometre is then used to test the strength of the block. If the block resists the penetrometre pressure then it is good to go. CSEB production turned out to be quite intensive as opposed to rammed earth construction.
Rammed earth wall construction
Rammed earth construction was a cakewalk after the two gruelling days of CSEB production. It consists of ramming earth and cement mixture using a rammer. The shuttering of the rammed earth is what requires a bit of skill. There are various parts and mechanisms that ensure the shuttering remains stable during ramming. The shuttering was built strong enough for us to climb up for pouring the soil mix in and ramming the mixture afterwards. Once we identified the soil components, we followed the same process used in the CSEB production for the rammed earth mixing. The ramming was the easy part as there are multiple instruments of various sizes that can be used for convenience. As far as cement is used for stabilisation, the soil is compressed enough and passes the pocket penetrometre test, the wall can withstand anything.
The experience at AVEI was indeed great with the opportunity to explore different construction techniques and the chance to interact with others having the same interests. You'd be surprised to know only 30% of the group were architects. The others were either civil engineers or other professionals who simply wanted to build their own homes. Having gone in eager to learn from the best, we came out much wiser and a little stronger!