Building rammed earth with bamboo and cotton fabric formwork / Earth Workshop Part 2 in Venice Architecture Biennale 2023

Fabric formwork made of bamboo and cotton fabric was used for building rammed earth at Earth Workshop Part 2 in Venice

Preparing earth workshop in Venice was challenging but very much rewarding. The difficulty of the workshop preparation lay in the special context of Venice. The delivery of any materials to Venice is longer and more expensive than inland areas being transported by boats and by foot due to many narrow alleys (They are even collecting bins like this way). Also, even something easy to get inland areas is scarce in the island, for example, Venice as a UNESCO heritage site rarely has a new construction, so it is very hard to get soil. Considering this context, I designed to deliver a 2nd earth workshop to build rammed earth with locally sourced materials.

The use of local materials was also a chance to show that fabric formed rammed earth is buildable with low-cost at a unique context like Venice. The use of fabric is one of great advantages of fabric formed rammed earth found through my PhD research. Compared to traditional rigid formwork using timber or steel, fabric is locally available, low-cost, lightweight, portable, and pre-fabricable. For this reason, a low-cost pure cotton fabric and bamboo sourced in Venice were used for building formwork for rammed earth; it is an experimental and innovative technology that has been yet explored and conducted. Although I built fabric formed rammed earth multiple times, I have not yet built formwork with these two materials before. I previously proposed using bamboo for building the formwork for rammed earth walls at the project Weave Senegal Elementary School, but I did not yet build formwork with bamboo. So, building formwork with bamboo and cotton fabric in Venice was a great chance to test out and demonstrate that rammed earth can be built with the proposed technology. In this sense, the workshop was not simply a learning opportunity for unskilled participants but also for myself, since I had to build fabric formwork with the materials I have never used before by learning the properties of them from scratch and also carefully devise a pedagogical method to deliver the innovative technology to participants.

Bamboo was procured in-person from the island Lido in the Venetian lagoon to be used for formwork for rammed earth

Getting materials for building rammed earth was one of challenging processes. When I visited Lido - the island next to Venice, plenty of bamboo was growing along the beach of Lido, so I decided to use them for formwork. Transporting bamboo from Lido to Venice was such a journey for me carrying such a long length of bamboo. Each bamboo was generally more than 3 metre length, and I did not want to cut or fold it. When I got on a bus carrying the bamboo, it almost hit one of a passenger’s head due to its long length, and I apologise to the passenger. After seeing this accident, an Italian bus driver said something to me. I could not understand what he said with Italian, but it was so obvious in the context that I could not get on the bus . Although I was refused multiple times to get on public transportation with the bamboo by bus drivers and vaporetto-rope-tying persons (I did this journey even twice), I managed to transport the bamboo by public transportation not damaging bamboo much without any further accident(!).

Bamboo was partially cut to bend

Partially cut bamboo was used to create a curved form but this structure was weak because the innate strength of bamboo was undermined

Once materials were procured, learning the property of bamboo was an essential process to build fabric formwork. Initially, I intended to build a rounded rammed earth stool. So, I partially cut bamboo section and bend it to create a curved shape. However, the cut bamboo was weak and broken easily since its innate strength was undermined by cutting. When I found that the first prototype does not work, it was less than 5 days before the workshop date. Instead of being frustrated, I was thankful for knowing this no later than 5 days before still having some time to build a 2nd prototype. I thought it is such a good lesson to learn how much it is significant to understand and utilise the innate property of materials instead of being against it. Therefore, I quickly dropped the initial design-driven approach and take a material-driven approach employing the inherent quality of the natural material.

Bamboo's stem becomes gradually slender from bottom to top as it is growing. The varying thickness of bamboo was used for all the components of formwork for rammed earth

Bamboo does not have a straight or standard form like manufactured timber like CLS or plywood, so the inherent heterogenous quality of bamboo was employed as it is for building formwork for rammed earth

Bamboo was joint with lashing technology without any nailing with a goal of creating low-technology

Varying thickness of bamboo was employed for vertical frames of formwork and these frames are sharing lateral earth pressure each other

Creating a simple and low technology was also an essential part of the formwork construction process, and it is closely aligned with the initiative of my PhD research that is to deliver fabric-formed rammed earth technology to flood or disaster-affected people so that they can build flood-resilient and sustainable earth homes with limited resources. Based on the initiative, bamboo was joined with lashing technology without any nails. As a natural material, bamboo stem becomes gradually slender from bottom to top, so the thick bottom stems of bamboo were used for the bottom and middle horizontal frames of the formwork to withstand the lateral force of earth pressure, whereas relatively thin bamboo stems were used for the top horizontal frame of the formwork since the lateral force is weaker at the top compared to the bottom and the middle. A medium and small thickness of bamboo stem was utilised for the vertical frame of the formwork. Therefore, a varying thickness of bamboo was all employed for building formwork. Being different from manmade manufactured timber such as CLS and plywood, bamboo has a heterogeneous thickness and shape; it does not have a straight form. Instead of altering bamboo’s form or using a uniformed shape to create a predesigned shape, I created the formwork made of various thickness of bamboo, carefully thinking about where they have to be positioned based on the lateral earth pressure and how they have to be connected to distribute the pressure.

Cotton fabric was hand-sewn to contain rammed earth

Sewing the fabric for rammed earth formwork in Scotland + Venice exhibition venue

The part where the fabric was joined was hand-sewn with a more strong sewing method to prevent the fabric from being torn

Cotton fabric was hand-sewn at the edge of the fabric to prevent from fraying. The joint where the fabric was connected was sewn with a much stronger sewing method to keep the fabric from being torn during ramming course. Once sewing is done, the fabric was pulled tight from bottom to top make it be stretched by bamboo frames. Creating the fabric formwork would have been faster if there had been a sewing machine, but it was absolutely doable to create fabric formwork with hand-sewing. While hand-sewing, I thought that fabric formwork could play an important role in involving a wide range of people with a different skillset in the disaster-affected context. In the emergency context, resources and facilities are lacking and people lose their pre-disaster jobs, so either men or women, skilled or semi or unskilled persons could be engaged to build fabric formed rammed earth with low technology and locally available resources.

Participants are pouring clay to a container to create soil mixture for rammed earth

Participants are pouring aggregates to a container to create soil mixture for rammed earth

The earth plaster panel created at Earth Workshop Part 1 was evaluated to choose an optimum soil mixture before building rammed earth at Earth Workshop Part 2

Building fabric formwork and a rammer was completely done before the workshop date, but I was not sure if the formwork would work okay or not for creating rammed earth as it was a first prototype formwork made of bamboo and cotton fabric. Therefore, I explained to the workshop participants that we would create rammed earth with a new technology and we would learn from its construction process regardless of whether it works or not. Before building rammed earth, participants saw the earth plaster board created with different ratios of clay and sand at the Part 1 earth workshop. The ratio of 1:6 (clay:sand) seemed to be quite sandy. When a ball-dropping test was done, the soil mixture with the ratio of 2:6 (clay:sand) had a lack of cohesion than the ratio of 3: 6. Therefore, for the soil mixture for rammed earth, we created it with the ratio of clay (1) : sand + gravel (2) – specifically, 2 baskets of clay, 3 baskets of sand, and 1 basket of gravel. But, the top layer of rammed earth was created with the ratio of clay (1) : sand (2) : gravel (1) due to a shortage of clay;  it was slightly sandy but still good to create rammed earth. Interestingly, this different ratio of soil mixture at the top made the final model beautiful with a different soil texture.

One of the workshop participants is compacting soil mixture within bamboo and cotton fabric formwork

Excessive moisture is extracted through the permeable cotton fabric during the ramming course and a small amount of soil mixture is pulled out from the small gap between the horizontal bamboo frame and the ground floor

The size of the rammed earth we created was approximately 40cm height x 22cm width x 22cm length. Participants were surprised that quite a large amount of soil mixture was used considering the relatively small size and how intensive rammed earth construction is – mixing dry soil mixture, mixing again soil mixture adding water, and compacting soil mixture hard with a rammer. They observed that moisture was extracted through the permeable cotton fabric during the ramming course, also saw that a small amount of soil mixture was pulled out from the small gap between the horizontal bamboo frame and the ground floor. That was because of a heterogeneous and natural shape of bamboo. Being different with manufactured timber like CLS or plywood having a standard and rigid shape, bamboo has nodes gradually slender from bottom to top. So, it was inevitable that a small amount of soil was pulled out between the gap between the bamboo and the ground floor; interestingly again, this made the rammed earth model look aesthetically appealing and this will be shown and explained in detail at the next posting.

Rammed earth was fully built at the Earth Workshop Part 2 in Venice

Bamboo joint with lashing technology and low-cost pure cotton fabric performed successfully as formwork for building rammed earth

The permeable fabric helps to extract moisture and dry rammed earth quickly

Rammed earth was fully built at the Earth Workshop Part 2

We completed building rammed earth successfully with the formwork made of cotton fabric and bamboo on a workshop date, and I was very much glad knowing that the first prototype formwork performed really great without being destroyed during the ramming course.

Pure cotton fabric used for rammed earth formwork was still in a good shape after dismantling the formwork, being reusable

Pure cotton fabric used for rammed earth formwork was still in a good shape after dismantling the formwork, being reusable

The formwork was dismantled a week after completing the rammed earth construction. After unlashing bamboo frames, fabric was removed by carefully cutting the sewn part. All the components used for formwork was still in a good condition after rammed earth construction, so they could be all reusable ranging from bamboo to cotton fabric and straps.

The full and detailed image of the rammed earth will be posted shortly.

Acknowledgement

I am really thankful to my God who has been with me and guided my heart and thought during my time in Venice as He has been always. Without His full guidance and comfort, I would not had been able to plan, design and build the new technology and deliver the technology at the workshop successfully, and also conduct my job as a senior exhibition invigilator in Venice.

I appreciate Scotland + Venice and Architecture & Design Scotland for their generous support for helping me to deliver both Earth Workshop Part 1 and Part 2 at the Scotland + Venice exhibition venue while I worked as Senior Exhibition Invigilator for the exhibition 'A Fragile Correspondence' that was held as part of Venice Architecture Biennale 2023.