Rammed earth is one of the oldest methods of constructing walls and still holds great potential for modern earth construction. One aspect of this potential is the gift of its colors and layers, which become visible as the formworks are removed, revealing a layered character. As a process that involves the layer-by-layer compression of gravel, sand, silt, and clay, its resulting appearance is a horizontal stratification of earth tones, material content, and curing procedures. This colorful appearance of rammed earth walls can be controlled and explored through patterns, texture, pigmentation, and natural clay colors, offering an opportunity to push its boundaries within architecture.
Different colors of rammed earth walls result from the varying soil properties found in different locations. The type of soil not only affects the mechanical properties of the rammed layers, where there is a direct relationship between the dry density and compressive strength of the material (the denser the material, the higher its strength) but also influences the appearance of the walls. This is because natural clay comes in different colors, including red, white, yellow, and purple. This makes it custom-built to the wealth of its soil resource and questions to what extent pigmentation is needed to create variance in its layers.
In a workshop conducted by Erika Alatalo, a Finnish architect, in collaboration with Doedoe, a Gambian artist, in the village of Karsi Kunda in the far east of Gambia, they focused on constructing rammed earth walls. This construction technique was unfamiliar to the community at the time. The workshop aimed to study the impact of the natural clay colors already present in the village, as well as the effects of introduced pigments on the soil type. Given the diverse local resources of clay colors in the area, they compressed each layer with a different clay color for one iteration. For the other iteration with introduced pigments, the appearance varied. The red and black pigments created a strong color, while the yellow, blue, and white pigments simply vanished into the mix. Despite the striking effects of the red and black pigments, the architect felt that they didn't blend well or look as nice as the ones created by the natural clay variations.
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Blending pigmentation effectively in rammed earth was a research question explored by Tobias Helmersson, a student from Chalmers School of Architecture in Sweden, in 2021. He conducted tests using red iron oxide, black iron oxide, and yellow ochre in varying quantities on small cubes. Interestingly, the yellow ochre resulted in minimal visual difference compared to the others, likely because it closely matched the color of his earth sample. Through his research, he found that allowing erosion on the facade of rammed earth walls can create a gradient of color. When high-pressure water is applied to a red rammed earth cube, the eroded pigment appears less red than the uneroded surface. This indicates that the color of rammed earth shifts as the depth of erosion increases.
The impressive work of Joelle Eyeson and her rammed earth construction company, Hive Earth, in Ghana, showcases a mastery of harmony and contrast using natural clay colors and pigments. Hive Earth strives to build accessible and environmentally friendly housing in West Africa, utilizing locally available materials. Their exploration of color challenges people's perceptions and preferences toward earthen materials. They skillfully design layers with waves and natural textures, blending earth tones and creating striking contrasts with pigmentation. Each wall construction is intentionally crafted, turning it into an art form, and every wall cast within a formwork is unique. In a previous interview with ArchDaily, Joelle explains, "Many of the colors you see on the walls are natural colors of the earth. In Ghana, we have a wide range of earth variations, allowing us to achieve light beige, gray, red, or even black hues. Sometimes, if requested by the client, we add iron oxide pigments to create brighter colors.”
Rammed earth wall finishes have a warm and atmospheric quality, with each iteration showcasing the richness of various soils. The interior of Nando's restaurant in Chesterfield is a prime example of how pigmented clay can be used to create vibrant colors and robust textures, enhancing the ambiance of a dining space. Another notable application is seen in the Hundertwasser Park Centre, Kawakawa, New Zealand. Its colorful layering is a direct representation of specific views in the local landscape, including ocean inlets and clouds. The versatility of rammed earth extends beyond buildings to furniture and interior fixtures. For instance, Local Collective designed clay seating for the London Festival of Architecture and Network Rail, layering different colors of local clay deposits in London. This public seating space allows people to experience and feel the natural qualities of the material.
Integrating more modern construction techniques in the deployment of rammed earth walls is the framework for futuristic explorations. While it has limitations, the malleable nature of rammed earth emphasizes its need to be shaped and designed in various forms within architecture. Therefore, exploring the harmony and contrast between natural clay colors and pigmentation serves as a starting point for reintroducing rammed earth into contemporary design. This approach highlights the need for intentional artistic processes within standardized construction practices and challenges users' perceptions of local earth materials in the global south.
