Building with Earth: Cast Earth, Cob, and Compressed Tiles
The front approach to the Mudhouse in Abetenim, Ghana
Ancient Origins and Contemporary Revival
Earth has been one of humanity’s earliest building materials, used for over 11,000 years in dwellings, fortifications, and cultural landmarks across the world. From the adobe houses of the American Southwest to rammed-earth fortifications in France and China, mud building has shaped civilizations. During the 19th and 20th centuries, however, industrial materials like steel and concrete stigmatized earth as a “poor person’s material” (Trummer 2021; CRAterre 2023).
Since the 1970s, architects and organizations like CRAterre have led a revival of earth architecture, promoting it as ecological, low-carbon, and culturally rooted (CRAterre 2023).
Construction phase of the Mudhouse in Abetenim, Ghana, showing completed cast-earth pillars. Local workers used bamboo formwork to shape the earthen mix, creating a series of structural columns that frame the building and give it both strength and texture.
Cast Earth: Monolithic Pillars
In the Mudhouse, the structure is defined by cast-earth pillars, poured into bamboo formwork and stabilized with small amounts of cement. Cast earth is a modern reinterpretation of rammed earth that allows earthen walls to be poured like concrete while retaining the material’s low embodied carbon. Studies show that stabilized earth walls can emit up to 80% less CO₂ than concrete while still offering durability (Structural design with rammed earth – a shear strength perspective, 2014).
For future iterations, the structural performance of the cast-earth pillars could be strengthened by adding a central stiffening post, which acts like a spine to resist rotation and buckling at the base. This could be paired with a more robust soil-to-concrete interface to reduce cracking where the pillar meets its footing, and with raised or capped plinths to protect the vulnerable base from moisture (Structural design with rammed earth – a shear strength perspective, 2014).
Local craftsmen shaping cob walls around a window opening during the construction of the Mudhouse in Abetenim, Ghana. The cob mixture of soil, straw, and water was applied by hand, layer by layer, giving the walls their distinctive textured finish while forming openings for light and ventilation.
Cob Walls: Hand-Shaped and Textured
Cob (soil, straw, and water mixed by hand) has been used for centuries from Devon, UK, to West Africa. In the Mudhouse, cob was chosen for the infill walls, producing sculptural, textured surfaces that express handcraft.
Despite its stigma in industrial contexts, cob is now celebrated for:
Thermal mass and humidity regulation, keeping interiors cooler and drier (Properties of Sustainable Earth Construction Materials: A State of the Art Review, 2021).
Participatory construction, where community members layer the walls, reinforcing social bonds (CRAterre 2023).
Improvements could include adding natural fibers such as hemp or palm strands to reduce cracking and improve tensile strength (Properties of Sustainable Earth Construction Materials: A State of the Art Review, 2021).
Interior perspective of the Mudhouse in Abetenim, Ghana, with compressed earth blocks laid as ceiling tiles.
Close-up of compressed earth blocks forming the ceiling of the Mudhouse.
Compressed Earth Blocks: Ceilings and Natural Cooling
Perhaps the most unique detail of the Mudhouse was the use of compressed earth blocks (CEBs) as ceiling tiles. CEBs are typically used as wall units, but here they were reimagined to span across the roof structure, doubling as both thermal mass and finish material.
Above the CEB ceiling, a ventilated air cavity was created by the corrugated metal roof. During hot days, this system acted like a natural air conditioner:
The sun heated the corrugated roof, creating rising warm air currents.
Cooler air from the shaded lower edges of the roof was drawn through the cavity.
This airflow pulled heat away from the CEB ceiling, while the thermal mass of the blocks stabilized the bedroom temperature below.
The result was a passive cooling system that kept the interiors comfortable without electricity, relying solely on the combination of earthen material and architectural detailing (Trummer 2021; Sustainability, 2021).
For future projects, stabilized or interlocking CEBs could further reduce shrinkage cracks and improve assembly.
Cultural Importance and Contemporary Use
United States: Earthen construction survives in the adobe traditions of the Southwest and in modern sustainable architecture experiments since the 1970s (Easton 2007).
Global: France, China, India, and Ghana continue to integrate earth as a sustainable alternative to concrete, reinforced by global climate goals (CRAterre 2023).
Cultural Value: Mud building emphasizes local craft, community building, and ecological stewardship, qualities that make it relevant in today’s search for low-carbon housing.
Lessons from the Mudhouse
Cast Earth: Effective but could benefit from improved plinth detailing and soil testing.
Cob Walls: Beautifully textured but requires moisture-resistant plasters for longevity.
CEB Ceilings: Doubled with a ventilated roof cavity, they became a natural cooling system.
The Mudhouse demonstrates that mud construction is not a relic of the past, but a global, forward-looking technology. By combining cast earth, cob, and CEB ceilings with passive cooling strategies, it creates architecture that is structurally intuitive, culturally grounded, and ecologically necessary.
References
Trummer, J. Timber-Clay Composite Slabs. Master Thesis, Technical University of Munich, 2021.
CRAterre. Plaquette CRAterre Pôle Habitat. CRAterre, 2023.
Jaquin, P., et al. Structural design with rammed earth – a shear strength perspective. Proceedings of the ICE – Construction Materials, 2014.
Zhang, Y., et al. Properties of Sustainable Earth Construction Materials: A State of the Art Review. Sustainability, Vol. 16, No. 670, 2021.
Easton, D. The Rammed Earth House. Chelsea Green Publishing, 2007.
COPA is an architectural design studio with offices in New York, Los Angeles, and Santo Domingo. We welcome collaborations with those interested in low-carbon, alternative materials—feel free to connect with us through our contact page.
Learn more about this project on the Mudhouse project page.
