My husband and I constructed a rammed earth house in southern New Mexico, USA. The property where the house was built had the correct mix of sand and clay. We watered the soil in place to get the correct moisture content. Then using a garden tiller, we blended areas where the earth had to much sand with those where it had too much clay. We shoveled it into a wheelbarrow then tamped (compressed) it by hand with a steel rod welded to a flat plate.

This is extremely labor intensive and physically demanding. It’s possible, though more expensive, to use a mechanized equipment to move the soil and tamp the walls. Our rammed earth walls were a foot thick to give enough bulk to be stable. In our case the house was passive solar and the thick walls provided the thermal mass needed for comfort. The walls were constructed on top of a foundation of cinder block filled ¾ full with concrete, to ensure that there would be no contact with standing water.

We initially designed forms suggested in a Rammed Earth book but discovered quickly that they could not withstand the pressure of the ramming. The walls bowed and had to be torn down. We had to design our own forms which were trickier than expected. Not only did they have to be extremely strong, they had to be lightweight enough to be stacked. The forms also had to be clamped together in a way that did not interfere with the ramming.

We loaded about eight inches of earth into our forms bucket by bucket. As the walls grew in height this became harder. Each bucket had to be hoisted up by rope and emptied. Once the soil was in the form it was leveled then compacted with the tamper. We could tell when the earth was fully compacted when the tamper bounces back from the earth instead of sinking into it and we could hear a "ringing" sound. The original eight inches of soil compacted down to about a 5 inches of final height. This was repeated over and over and OVER. This is a LOT of work. After one form was compacted, about 3 feet of wall, a second form was stacked on top and another 3 feet was rammed. The process was repeated for the third layer. The walls were constructed in sections. Special forms were constructed for the corners as we did not want a joint at this critical location.

A bond beam was poured at the top of the rammed earth walls as a point of attachment for the roof and to maintain structural integrity at the top of the walls. Forms were constructed and cement was pumped up through a long hose. Local building code required that the bond beam be at least 6 inches deep. (The building inspector did check it too).

One consideration with rammed earth is that the plumbing and electricity has to be embedded in the walls. We installed plastic PVC for most of it as we were ramming the walls to minimize the channeling needed. This meant that extensive planning had to be done ahead of time for every outlet and water pipe.

The interior walls can be finished in a variety of ways, from natural clay washes to more standard surfaces. Our walls were finished with a plaster surface then painted with normal latex paint (reducing the air quality but at this point we were too exhausted to consider a natural wash). Saltillo tile was used on the floor, as it has good solar thermal qualities.

A two inch layer of foam insulation was nailed to the earth wall then stucco was applied to the foam walls. This outer layer is important to protect the walls from erosion and from heat loss. We chose artificial stucco which allowed for more expansion and contraction. The earth walls although strong enough to support a roof and live in will continue to cure for years.

The project took 2 years to complete with just us, a husband and wife team, as builders. It was completed in 1995. We hired out the foundation, plumbing, the concrete pump for the bond beam, plaster work on the interior walls and ceiling and the exterior stucco. Everything else was done with our own two hands.

We had to sell the house soon after completion but the current owners report that there have been no major construction problems. The plaster on one bedroom wall has a tendency to crack, which in hindsight does not surprise us as it was the one wall that did not “ring” quite the same as the others.

Here are some websites for reference:

Current earthen building codes & practices: http://www.fawebster.com
Basic building techniques and Q & A: http://www.greenhomebuilding.com/rammedearth.htm