Adobe brick experiments started at Sacred-Groves site with an eagerness to see the completion of the Xaher house, a humble and pretty home being built on the lines of zero investment/’Build free’ concept. A number of Saced-Grovians have contributed their free time for the development of the Xaher house but the progress was very slow. With a vision to complete the Xaher house soon Sarin and Minky, two volunteers started making adobe bricks according to traditional method that requires long rice straw because it was readily available at site.
Prototype houses that were being made in cob was facing pressures as the deadline was crossed. To speed up the construction the usage of adobe brick to construct walls of 2nd floor level seemed like a good option. The prototype houses require quality work and materials. Thus an elaborate research and experimentation on adobe bricks was initiated to arrive at a good quality adobe brick.
The sub soil 2ft underneath the ground was dug out at our own site. With the sedimentation test the soil was found to be good for construction. Any soil good for construction should have 15 – 25% of clay, 5 – 30% of silt and around 60% of sand and should be devoid of any organic matter.
The required specifications:
The remaining portion of the building required a 30cm thick masonry wall at the second floor level. So bricks of size 45X30 were chosen to make a single brick thick masonry wall.
The materials, proportions and sizes:
Different mixes were prepared with permutations and combinations of earth with fiber materials viz. long rice straw, chopped rice straw, rice husk and two combinations of rice husk and chopped rice straw (one with the ratio of rice husk and chopped rice straw being 1:2 and the other being 2:1) in the ratio of 6: 1 respectively. The mix was then filled in moulds of 3 different thicknesses that are 5cm, 6cm and 7cm and was dried under the sun.
Observations and improvisations:
Most of the bricks cracked as they were directly dried under the sun. Thus another batch of bricks were made and they were dried under a shade for couple of days and were then shifted under the sun for losing the residual moisture. However it turned out that bricks with thicknesses of 5 and 6 cm developed cracks as they were too thin.
The bricks that did not crack were tested for the maximum compression load they can bear.
Testing the sample bricks:
A foldable ladder was used as the tool to hold sample bricks. A weighing machine was suspended by a rope tied to the sample brick. And a barrel was then hung on the weighing machine.
The barrel was filled with water liter by liter (1 liter of water weighs 1 kg) until the brick gave up and broke into two pieces.
Watch the brick testing videos: https://youtu.be/I076BeXeURI
The load bearing capacity of all the sample bricks is listed below
The combination with less rice husk and more straws revealed to be the strongest. Taking into consideration the ease of production, the sample with only rice husk was chosen to be used subsequently.
Yet there was room for improvisation…
Although a good result was arrived at after rigorous tests and experiments there were some short comings. Passing and lifting the bricks was found to be inconvenient because of the weight. Thus the size was reduced to 30X20X7 cm.
Mass production of bricks:
– 6 parts of soil and 1 part of rice husk is mixed together such that rice husk gets distributed evenly in the soil.
– A pit is made in the middle of the dry mix.
– Water is poured in the pit. A gap of 5 minutes is given so that dry lumps of soil absorb water. That way they crumble easily and thee will be no dry soil in the mix.
– At first mixing is done with hand and then it is stamped with feet to break some stubborn lumps.
– Water is gradually added as and when required to achieve a good consistency.
– The consistency of the mix should be such that the mould can easily come off once filling is done and the shape of the brick should remained intact without collapsing after the mould is removed.
– Mould is wet in water before the mix is poured so that the mix doesn’t stick to it. The mould should have smooth inner surfaces.
– The mix is put in the mould and compacted using fingers to avoid any air gaps. The surface should be made flat. Putting mix in the mould should not take a long time as the mix will dry and gets stuck to the inner surface of the mould.
– Lifting the mould is done carefully enough to keep the shape of the bricks intact.
– The bricks are let to dry under shade until they can be lifted without spoiling the shape.
– The bricks are then kept vertically and dried under the sun for a minimum of 2 days or until all the moisture is lost. Placing the bricks vertically helps the bricks to lose moisture very fast.
Storage of bricks:
Making sure that the bricks are totally dry before they are used in masonry is very important because the bricks shrink when they are drying. This will lead to cracks in the walls. Thus it is made sure that bricks have lost all the humidity and then they are stacked and stored under shade to prevent them from getting wet by rain.
Construction of adobe wall at Sacred Groves:
The second floor level was designed in such a way that the palmyra pillars took most of the load of the sloping roof and adobe brick masonry took the rest of the load. The palm pillars were rested on an earth-crete beam and the adobe masonry wall had to be raised on the earth-crete beam.
Preparation of mortar:
In the heap of sub soil a pit was made in the middle and water was poured into it. Before mixing, soil was left to soak up water for around 15 minutes. It helps in breaking the lumps easily and thus the mortar will be devoid of any dry lumps. Then the mud was stamped with to make a wet watery mix and was transported to the second floor level using pulleys.
Preparation of the surface:
The earthcrete surface was wet with water and moistened. Moistening the surface is important as it absorbs moisture from mortar if it is not wet.
Laying the bricks:
The earthcrete beam is 45 cm thick and we had to build a 45 cm thick wall up to the cill level and then a 30cm wall up until the roof. We started with tying a reference thread for the first brick course. At the two ends of every adobe wall portions a reference brick was laid. To get the alignment of the rest of the bricks straight we tied a thread from one reference brick to another. The rest of the bricks were laid following the alignment of reference thread. After the first brick course is done the alignment was done by dropping the plum bob to the lower layer for reference. As leveling each and every course is not necessary and doing so also slows down the pace of construction the horizontal level was checked only at the top three courses using a spirit level.
• The thickness of mortar should be at least I”.
• The total error in vertical alignment should not exceed 1″.
Arrangement of the bricks:
Until the sill level we had to achieve a thickness of 45 cm and thus we used alternating header and in a manner that mortar gaps remained staggered according to the drawing shown below.
After the sill level we used single brick thick masonry with vertically staggering alignment with header flushing the surface as shown in the drawing.
Before laying mortar for the next course of brick we made sure that the lower surface was not too dry to absorb moisture very quickly from mortar. The mortar should always dry in an optimum pace. If it dries fast it loses strength but its always better that it dries slowly provided there is enough time.
Joining the wall to the pillar:
After every four courses we drilled a 6″ hole horizontally inside the palm pillars. A 1′ rod with 10mm dia was hammered into the hole and was fixed to the wall by aligning the rod in such a way that it was placed inside the thickness of mud mortar.
At the curved portions of the wall:
The bricks at the curved portions of the wall had to be cut to achieve the wedge shape. Before laying every brick the shape was decided in reference to the previous brick and was shaped accordingly. And the vertical arrangement of bricks was such that the mortar gaps staggered. Because there was no standard shape for the corner portion of the wall there were huge mortar gaps occurring in between the wedge shaped bricks. This gap was filled with mortar in which broken brick pieces were inserted and compacted like random rubble masonry in a tiny portion.
Maintaining the adobe walls before plastering:
Since the adobe bricks we used were not stabilized it is prone to damage if exposed to rain before it is plastered. Thus it was covered with tarpaulins neatly every day so that no rain water touches the wall surface.