The Test Wall
The first wall
After failed to make a test block with adequate strength, I started working with the basics all over again. I read more, experimented more. And consulted few building codes for Rammed Earth structures. I could find that the soil selection was right. Still, the test blocks were weak with 10% of cement. The one thing that had a chance for improvement was compaction. With the form I made, it was not easy to compact the soil with a rammer. So I had to redesign the form that would guide the rammer.
I used a penetrometer (an instrument to test the amount of compaction in our case) to check the compaction. I made sure that the blocks were compacted to the maximum extent possible. Made many test blocks with different mixes and moisture content. Some of them were small blocks for erosion tests.
This time, the test results were good enough for a two-story building. Then I spent some time designing the formwork. The one I made was not sophisticated but was good enough to build a 3 feet high wall.
I could find the practical issues with the formwork when I started to build. When the design was inadequate, I halted building walls and reworked the form. It took three days to work and to build the first wall which only 3 feet high. The first wall looked good when the formwork was removed. After curing the wall for a week, it looked sturdy. The first thing I tested was how the wall handles the splashing of water. The wall handled that pretty well.
To this day, people use to ask me what happens when a Rammed Earth wall is exposed to rain. Contrary to common belief, the rain will not wash away a Rammed Earth wall, provided the wall is built with the right soil, right compaction, and right stabilization.
Generally, water will not get into a well-built Rammed Earth wall easily. But long exposure to rain can erode the walls. Though it will not weaken the wall, long-term erosion can spoil the look of the walls. It is always a good idea to protect Rammed Earth walls against rain. There are many studies done on the durability of Rammed Earth. An interesting one among them is ‘Durability of rammed earth walls exposed for 20 years to natural weathering’
After 20 years of on-site exposure to weather, the material loss due to wall erosion is measured by an innovatory method using the stereo-photogrammetry. The erosion measurement is equivalent to a mean thickness of about 2 mm (corresponding to 0.5% wall thickness) in the case of the rammed earth wall stabilised with 5% (by dry weight) of natural hydraulic lime. Therefore the stabilisation enables to not use any plaster to protect the walls. Bui,Quoc-Bao & Morel,Jean-Claude & Reddy,B.&Ghayad, W. (2009). Durability of rammed earth walls exposed for 20 years to natural weathering. Building and Environment. The research concludes that the erosion to exposed Stabilized Rammed Earth wall is very limited that the walls did not require any plaster as protection. And the authors say erosion can do more damage to reinforced concrete than to a Rammed Earth wall.
Unlike the industrial building materials (for example, steel or reinforced concrete) in which erosion has to be very limited to ensure its mechanical performance, in the case of rammed earth walls, erosion is tolerable. Bui,Quoc-Bao & Morel,Jean-Claude & Reddy,B.&Ghayad, W. (2009). Durability of rammed earth walls exposed for 20 years to natural weathering. Building and Environment. Two reasons can be attributed to the disbelief people have on mud walls. First, when they think of a mud wall, they think of a Cob. Second, many of us associate soil with dirt. These are the factors that prevent one from understanding a Rammed Earth wall.
Worst yet, some Americans call soil ‘dirt’. Soil is not dirt. Dirt is what we wash away while bathing. Around 4.5 million years, the earth was formed. Then, at a point in time, the earth had no soil. It had only rocks. As time passed, soil formed due to weathering of rocks. So every soil has a parent rock. Only when we associate soil with rock, we can understand the strength and durability of a Rammed Earth building. Because, when a Rammed Earth is built, an artificial sedimentary rock is created by the process. In the process, the soil is densified where clay acts as a glue to bind the particles (A small amount of cement added fills the voids left).
The strength of cement stabilized Rammed Earth wall does not come primarily from cement, but a small amount of cement can help the wall to gain strength and guards against rain. But any amount of cement that is more than required will interfere with the thermal properties of the wall. Having the right balance is key. Many Rammed Earth Structures without cement have survived centuries. Using lime with high clay soil can yield durable walls.
A Well-built Rammed Earth wall is a kind of sandstone. The picture shows a broken wall that shows highly compacted soil grains. I built, broke, drilled, and cut walls to see how good they were.
I was all set to start building 3 feet stem walls. The next resource I needed was labour. Labour is the major proportion of the cost of a Rammed Earth building. I have seen many times Western builders saying that a Rammed Earth building would be cheaper in developing countries. Believing the labour cost is much less in India is a mere western perception. In the Indian state I live in, labour is neither cheap nor abundant. In many places, people prefer migrant labour from north India for cost-effectiveness.
In my case, there was no experienced labour for Rammed Earth available. I decided to recruit a few agriculture labourers. I thought they were a clean slate so that they could be trained. Labours from regular building work were not easy to train. For them, building Rammed Earth is a ‘heavy work’.
Rammed Earth can be built with semi-skilled labourers provided there is one skilled person available for quality control. Working with the soil requires a basic understanding. Labours should strictly follow the guidelines while mixing, moisturizing, and compacting. Any deviation from the procedure could drastically affect the strength and durability of the walls. There is a difference between brickwork and Rammed Earth. If a Rammed Earth wall built with defects, it can not be fixed easily. Freshly built walls become too hard to work with after a couple of hours.
Though there were people with impressive building skills, most of my experience with the labourers has not been very satisfactory. They used to assume everything they were building was going to have a cosmetic fix like plastering and painting. A Rammed Earth wall does not have any finish after the removal of formwork. It was hard for construction labour to unlearn things. In my experience, labourers with no prior building experience would be better to employ, where there are no experienced earthen building workers available.
I engaged a couple of masons to build these brick lines to guide the Rammed Earth wall, but I had to demolish and rebuild myself as these brick lines were not straight. (The lines never met at a right-angle where they had to). The reason I engaged masons was to build them perfectly, but that did not work that way. From that point, I started to build, to use small tools that would help to build things with unskilled labourers.
Then I started building with a small team of unskilled labours.