I just finished a research about an old technique for building walls which we should keep alive and try to spread all over the world. I’m talking about rammed earth.

Together with its “sister” solutions, namely adobe and earth bags, rammed earth is a very eco-friendly alternative to the conventional wood or concrete framing.

Evidence of the early use of rammed earth has been seen in Neolithic archaeological sites along the Yellow River in China, dating back to 5000 BCE and much of the Great Wall of China is made using an earlier method of rammed earth construction.

From my previous studies I have knowledge of rammed earth constructions in the Portuguese tradition as well as in the Australian aborigines' past. In the southwestern United States, adobe walls far exceed the use of rammed earth, but now the latter is starting to appear in building codes.

Rammed earth is a method of building walls whereby a mixture of earth is compacted in layers between a temporary frame, usually made of wood or plywood; it must be sturdy and well braced, and the two opposing wall faces clamped together. Damp material is poured in to a depth of 4 to 10 inches and then compacted to around 50% of its original height.

Most rammed earth builders use pneumatic rammers to compact the earth within the forms. As each form is filled, another form is placed above it, and the process begins again. Once a wall is complete, it is strong enough for the frames to be immediately removed. Construction is best done in warm weather so that the walls can dry and harden.

The soil mix needs to be carefully balanced between clay, sand and aggregate.  Modern advances in the technology include the addition of a small percentage of cement, better structural design methods, the inclusion of damp courses and concrete footings and regulatory controls by building authorities. It is also possible to add a water repellent admix to the soil mixture.

The soils used are typically subsoils low in clay. Clay/sand ratio has the greatest contributing effect on how well an earth wall will perform.  Traditionally it has been established as 30% clay and 70% sand (when using cement as a stabilizer, clay content can be reduced as low as 8% to 10%).

Most site soils can be used in some proportion to create a useable formulation, checking first gradation, USCS soil type, and in some cases a plasticity index.

Clay particles help to bind together the soil matrix. Coarse sands with a good distribution of particle sizes are usually better than fine or uniform sand.  Cracked or crushed gravel is better than “pea” or river gravel because of its angularity. 

Because of their thickness and density, rammed earth walls provide high thermal mass: this means that heat or cold penetration of the wall is very slow and the internal temperature of the building remains relatively stable. Thickness and density also provide great noise reduction; plus earth doesn’t burn, is non-toxic, non-polluting and ‘breathes’. On the other hand, rammed earth homes might take more work to meet with approval by building officials, bankers and insurers.

Given the many advantages of this solution, why isn’t it widespread and records so few cases of use, in Italy for example? Is rammed earth not adaptable to many conditions? Or more likely the building regulations tend to exclude it to be better protected and cautious? I‘ll keep researching.