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What counts as raw earth? How we chose the projects for the guide
Many buildings are called earth buildings, but not all of them are. Before selecting projects for the Best Practice Guide, the partners defined what raw earth means and what a good example should teach.
Earth has been used for building for thousands of years, in rammed earth, adobe and cob. Robots and 3D printers now let us shape it with a precision that building by hand could not reach. The appeal is clear: local soil, little transport, almost no waste, low embodied energy and, at the end of its life, a material that can return to the ground.
In construction, however, “raw earth” is not a well-defined term. Some projects presented as earth architecture contain large amounts of cement or irreversible additives. For students and professionals, this is confusing.
Raw or stabilised
Led by Vertico, with input from Universidade da Beira Interior, the partners sorted printed earth by how the material behaves, not by where it comes from:
- Class A, raw: clay, water and reversible process additives only, with no hydraulic binder. Soaked in water, the material turns back into mud. It is fully circular.
- Class B, stabilised: a binder such as cement, lime or geopolymer, below 8%, added for faster printing or weather resistance. The material is more durable, but no longer reversible.
Above 8% binder, the clay is fully encapsulated and the material behaves like concrete, with earth acting only as aggregate. Projects in that range were left out of the guide, as were fired elements such as bricks and ceramics, because firing is energy-intensive and irreversible.
What makes a good example
Each candidate project also had to answer two questions:
- How was it printed? Projects are described by the type of machine (for example a SCARA system or a six-axis robotic arm) and by how the material reaches the nozzle (pump and screw, or jetting), not by brand.
- Can a learner see how it was made? The printed layers had to be visible, or documented in photos taken during construction.
Three kinds of projects
The guide labels every project by what it offers the reader:
- Accessibility: small, low-cost work in raw earth that a student or a small workshop can attempt.
- Applicability: walls, houses and pavilions that show how the technology works at full scale on a real site.
- Aspiration: complex, state-of-the-art projects for architects, engineers and researchers.
Most of the selected projects are Applicability and Aspiration examples. They range from a robot printing a noise barrier along a Dutch motorway to research prototypes developed in university laboratories.