Build with Gambia Earth Architecture Workshop: Experimenting with local materials in rural Gambia

It’s been three years since I graduated and left Europe in search of inspiring projects and ways to use my architectural skills on a grassroots level. During these three years I have volunteered in more than 20 projects and each of them has taught me more than I could have imagined. But the project that has taught me the most by far has been Build with Gambia, an earth architecture workshop that I spent most of 2018 leading in a small village in Gambia. The main goal of the workshop was to share knowledge in a mixed team of local workers and international volunteers while experimenting with different ways of building with local materials, in particular earth. The workshop took place in the village of Karsi Kunda in the far east of Gambia, where we designed and built a dormitory for a new rural vocational school called Kantora Arts Village.

This article focuses on the technical side of the construction, while a follow-up article will discuss the social aspects of the workshop. The main techniques we experimented with were rammed earth, adobe bricks, the Nubian vault, lime plaster and stone foundations. Continuously adapting the design and the way we worked to the local context was crucial, and plans and the design changed many times along the way as we learned more about the materials we were building with.

Design through experimentation in the local context

Gambia is the smallest country in mainland Africa, and yet it takes more than 10 hours to get from the capital Banjul to the village of Karsi Kunda by public transport. The remoteness of the village in such a small and poor country makes it expensive to build houses with industrial materials like cement blocks and corrugated roof sheets – materials that also have high environmental footprints. This is why finding ways of working with local materials was one of the main goals of the Build with Gambia workshop.

Only by working in the local context is it possible to find the best way to build with local materials. For this reason I came to Gambia without a ready-made design. Instead, the design of the dormitory was developed on site and it evolved greatly throughout the entire workshop.

There are many ways of building with earth and first we had to find out what was the best technique in this context. In order to find this out we started by building a small shelter that could later function as the living room of the dormitory. Building this shelter gave us the opportunity to test, learn and improve different techniques before using them in the main dormitory building.

One reason for this initial experimentation and the shelter was to develop the design of the dormitory in a way that let the locals express their opinions and ideas about the way we built. As the locals participated in the construction of the shelter, they could gain a better understanding of the techniques used and with their knowledge of the local context they could suggest improvements.

The international workshop participants were mainly architects or architecture students, and hence they could also contribute with valuable ideas. For example, one volunteer from India built a clay oven which he then used to try and bake clay bricks that we could use to tile the parapet of the roof for better waterproofing. The bricks didn’t turn out well, probably because the oven was not hot enough, but the oven itself became a feature of the dormitory. While building the oven we also experimented with using crushed and whole seashells in the plaster in hopes of creating a more water-resistant surface.

Rammed earth experiments

I initially wanted to create the whole design while in Gambia in order to better match the local context. However, the funding of the project relied on donations from international workshop participants, and in order to promote the workshop and find participants, I had to decide the main technique I would use in the building before coming to Gambia. I chose rammed earth, mainly because I felt most familiar with it at the time, having learned a lot about the technique while volunteering in Mexico.

For the locals in Karsi Kunda, rammed earth was something completely new. The first tests were done in the shelter where we made benches using different mixes of earth and sand, either with or without lime or cement for stabilization. In the end we decided to go with an unstabilized mix for the dormitory, using a mixture of one part filtered sand and one part filtered earth.

One local resource we discovered was that the area had many different colors of clay, including red, white, yellow and purple. The locals sometimes use these clays, particularly the white clay, to add a thin decorative plaster on their adobe houses. We wanted to take this resource and see what else we could do with it. Rammed earth walls are built in layers and we decided to experiment with making a wall where each layer has a different color. We also bought some paint pigment and experimented with adding it to the mix.

For this part of the workshop I invited Doedoe, a Gambia artist I met while visiting Tunbung Art Village, to join us and guide the construction of the colored wall. The results with the paint pigment varied, with the red and black pigment creating a strong color while the yellow, blue and white pigment simply vanished into the mix. But even the pigments that did work didn’t look as nice as the ones created by the natural clay variations. After trying different ways of mixing in the clay, we discovered that the best way to mix the clay was to soak it in lot of water. The problem with this approach was that the resulting mixture was too wet for rammed earth, but we could use the mixture after leaving it out to dry for a while.

The design of the dormitory that I developed after building the shelter had a mix of rammed earth and adobe walls. There were many reasons for this, one being that building with adobe bricks was much faster as the locals were already familiar with the technique. One challenge we had with rammed earth was that it was difficult to make a strong enough formwork with the wood we had available. Because the formwork was not strong enough, the resulting walls had weak spots. Wood is also expensive to get in the village, and it was clear that this was not a technique the locals could afford to use in their own houses.

While building the walls of the dormitory we encountered more challenges with rammed earth, including more problems with the formwork and challenges with keeping the wall dry during the rains. Eventually, we switched completely to adobe bricks, the technique that the locals use and that indeed works very well in the local context. Rammed earth may be popular with architects, but it was not the best solution in this context.

Learning to build a Nubian vault

Already before reaching Gambia I realized the roof would be a big challenge. Almost all roofs in rural Gambia are covered with either thatch or corrugated metal sheets. The problem is that thatched roofs only last a few years before they need to be replaced, while corrugated roof sheets are hot and low quality. What’s more, both of these roofs require timber and sourcing wood in the villages has gotten both difficult and expensive due to deforestation and desertification. Inspired by the work of the Nubian Vault Association in Burkina Faso, I realized that building a Nubian vault would also be ideal in our case.

The Nubian vault is built with adobe bricks using a technique that requires no formwork, meaning it is possible to build a roof without any wood, steel or cement. None of us had ever built a vault before and one of the main reasons for building the shelter was to see if we could even do it. We started without a formwork, but soon it was clear that the way we were laying the bricks would not work for long without a formwork. Wanting to complete the vault, the locals improvised a formwork using the wood from our rammed earth formwork and some bamboo mats we had available at the site.

Finishing the vault with the formwork was not the Nubian way but it was simple and quick. However, soon after finishing it became clear that the vault was not very strong. The mortar joints were too large, the bricks didn’t overlap the joints enough, and the shape of the vault was too semi-circular rather than catenary. For these reasons, the vault developed large cracks almost immediately after it was finished. We decided to take down the vault and to try again.

We built the second vault after I had visited the Nubian Vault Association in Burkina Faso, and hence I had a better understanding of the technique and the mistakes we had made. Following a manual the Nubian Vault Association had shared with me, we used smaller bricks, reduced the size of the mortar joints and created a catenary shape. On the roof we placed a plastic sheet for waterproofing and then plastered above the sheet.

Even though we now knew better what we were doing, there were many challenges with this second vault as well. The string we used to create the catenary shape was too flexible and the resulting shape was not very symmetrical. Placing the plastic sheet was also challenging, and during the rains we saw that water could enter the structure from the sides. Eventually this vault also developed cracks, although much smaller than in the first vault and we left the vault standing. The cracks could be caused by the uneven shape, or also by the supporting side walls being too thin.

Leaning the bricks on each other at a 60° angle was also more challenging than we thought, and sometimes the bricks at the top would fall off after placing them. For this reason, progress was slow as we could only do a couple arches before we had to leave the structure to dry. This element of time is what proved to be the greatest challenge in our case, and in the end we had to abandon the Nubian vault design for a different kind of roof, in order to be able to finish the construction on time.

Promoting lime as an alternative to cement

During the rainy season there are heavy downpours in Gambia, and protecting earth walls from the rain is essential for extending the lifespan of buildings. Usually this is achieved with roof overhangs, but as we were building a Nubian vault this was not possible. The Nubian Vault Association uses bitumen-earth plaster to make walls and roofs waterproof, but as with many other materials, bitumen was not easy to source in Karsi Kunda. Instead, we turned to lime, an alternative to cement that has the benefit of being CO₂ neutral over its lifetime, unlike cement which is a major contributor to CO₂ emissions globally.

Lime is usually made by burning limestone, but the lime we used was produced in Gambia by burning oyster shells. By contrast, the cement used in Gambia generally comes from Senegal, and so using this lime was a way for the project to support a Gambian industry and the local economy. This oyster shell lime is not very common in the part of the country where we were working and we had to order it specially from the other side of the country – and yet it still proved to be more economical than buying cement.

We used lime for many purposes throughout the workshop but the main use was for plastering. Adobe walls in the village are often plastered with cement in order to protect the structure from rain. This works well for a few years but eventually the plaster falls off, due to the earth expanding and contracting at a different rate than the cement. Lime plaster on the other hand is more flexible, which makes it more durable and less likely to crack on earth walls.

As none of us had used lime plaster before, we first had to experiment to find the right mixture, and once again the shelter was our testing ground. We started by mixing the lime with both sand and clay, but this plaster cracked a lot and we realized it would be better to use only lime and sand. The best results were achieved when we left the wet lime and sand mixture to settle for a week before use, otherwise cracks still appeared. Adding small amounts of different clays allowed us to create plasters in different colors, once again taking advantage of local resources to create a more interesting design. For additional water-resistance, we also added waste engine oil to the plaster mixture.

We also used lime in the foundations of the dormitory. The Nubian vault required large foundations, in this case 70 cm wide and 60 cm deep. The main material we used for the foundations was stones, first with mud mortar below ground and then with lime mortar above ground to create a water-resistant plinth.

We spent a lot of time placing the stones so that the gaps between them were as small as possible, so that the structure would be strong even if the mud mortar gets wet. Most adobe houses in the village don’t have foundations which results in walls cracking easily. Using stones in the dormitory was a way to showcase a simple way of making strong foundations with locally available resources that the locals can do themselves, even without the lime plinth.

Adapting to challenges

Throughout the workshop we faced many challenges that we had to adapt to. One of the challenges was that we were mainly building during the rainy season. Some days we couldn’t work because of this, but the main problem with the rains was when it rained at night when no one was at the construction site. We always covered the structures and adobe bricks with plastic sheets, but strong winds before the rains often blew off the plastic and caused a lot of damage. The adobe bricks also took a long time to dry, even when they were protected from the rain.

Time was another challenge, even without the delays caused by the rainy season. Working with local materials in a sustainable way was one of the goals of the workshop, but sourcing these materials took a lot of time. Each stone for the foundations had to be picked by hand and transported on a donkey cart, each wheelbarrow of clay dug with a shovel, and each bucket of water manually lifted from a 27-meter deep well by rope and pulley. Eventually we did learn to do things more efficiently, largely thanks to ideas from the locals who were used to working in this context.

Another major challenge was that finding international workshop participants proved to be much more difficult than I had expected. As a result, we didn’t have enough manpower or money to complete the dormitory according to the original design and for a while it looked like we couldn’t complete it at all. Eventually, I managed to find enough volunteers and to fundraise additional money to complete the building, but the Nubian vaults would have taken so much time and labour to build that we couldn’t afford it and so we had to come up with an alternative.

After considering a thatched roof and corrugated metal sheets, we eventually decided to build a flat roof using a palm wood structure and bamboo mats covered with a lime-earth mixture. Palm wood is commonly used in Gambia for roofs as it is very resistant to termites, while bamboo mats are commonly used for fences and outdoor seating. The roof we built also had a plastic sheet below the lime mixture for rainwater proofing, and we created a small slope for rainwater runoff by tilting the palm wood structure. However, the local workers were unsure whether this structure would survive the heavy rains of the rainy season, and after I left they added a second roof structure using corrugated roof sheets and timber donated by another workshop group.

But probably the biggest challenge was working with the locals, both at the construction site and in the village. Getting the locals to understand what we were doing and why was particularly challenging. But at the same time, working with the locals was also the greatest strength of the project. These and other social aspects of the workshop are a whole other topic that I will discuss more in another post.