The first thing you’ll notice about a rammed earth wall is how beautiful it is. The massive walls, with vivid waves of rich color, are striking and unique. Beneath the stunning surface lies a clever building system, offering energy efficiency and strength.
The History of Rammed Earth
The tradition of packing earth to build a wall dates back to the Great Wall of China in 220 b.c. Similar to adobe or cob, rammed earth is a mixture of clay and sand. But the tightly tamped material is a big difference from those other materials.
The tradition of using earth to build homes has been around for thousands of years. Large ancient structures, such as temples and mosques, were built of rammed earth throughout the Middle East. The pharaohs of Ancient Egypt ruled over cities constructed of rammed earth.
In the United States, rammed earth was popular from 1780 until around 1850, when the introduction of mass-produced bricks and cut lumber became readily available. These industrial materials allowed easier, faster construction of homes to meet the needs of the growing population.
Rammed earth had a brief resurgence during the sparse 20-year period after World War I through the Depression, when people could build their own homes using nothing but the local dirt.
The demand for manufactured housing at the end of World War II brushed natural methods like rammed earth aside. It wasn’t until the energy crisis of the 1970s that builders rediscovered using packed earth to build homes. Green builder David Easton single-handedly popularized the modern use of rammed earth through his many books on the subject.
What Rammed Earth Is
Rammed earth is essentially just man-made stone. But instead of being compressed for hundreds of thousands of years like sedimentary rock, rammed earth is formed in mere minutes through the compaction of dirt.
Rammed earth construction is a simple, yet labor-intensive, process that begins with the erection of formwork over the foundation. The foundations are the same as they would be for any home, but they must be sized to support the weight of the finished wall.
Forms can be made of plywood, metal, or fiberglass. The forms are held together with large bolts or bracing on the outside (see below). Formed to be at least 1 foot thick, finished rammed earth walls have a very flat surface because they take on the shape of the formwork mold.
Rammed earth walls are formed by packing, or tamping, a mix of soil with a tiny amount (around 3%) of Portland cement. The cement acts as a binding and strengthening agent. This mix is dumped into large wall molds, called formwork, in 7- to 8-inch-high rows, called lifts. A device that looks like a jackhammer with a manhole cover stuck on the end, called a tamper, is used to compact the soil into the formwork. Each lift is tamped down to half its height.
The wall rises slowly — an 8-inch lift at a time — until it’s complete. The forms are reused over and over again. ....read more