Dirty Work is Afoot

   I spent a few days a few weeks back assisting my son in building a 10 feet by 20 feet rammed earth cabin. It involved some serious manual labor, shoveling dirt, gravel and cement into a mixter, adding the correct amount of water, then mixing it all until the water was evenly distributed.  I was quite happy to oblige, when after a few days of hard labor, they determined that the most helpful thing I could do was to take their kids off their hands for a week.

    Rammed earth construction has been around for a very long time. It simply involves mixing some dirt with a little water, then pounding the dirt into a form.  It is a little more complicated than that, but not a whole lot. The dirt has to be the right mixture of sand and clay. In my son’s case their soil contains a lot of clay. Therefore, they are mixing equal parts fine gravel with their native clay soil. After some experimentation they determined that 3 shovels of gravel and 3 shovels of their clay soil, mixed with a little less than a quart of portland cement and about a half gallon of water, produced a mixture with the right consistency. The cement serves as a stabilizer and makes the wall more resistant to moisture.

John Tunnell screening the native clay soil to remove clods, sticks, roots, etc

My son, James, working at the top of the form, added the mixture and tamped it into place

      They poured a very stout foundation for the cabin, 18 inches thick. I’m not sure how deep the foundation is. There are 3 foot long pieces of rebar sticking out of rhe foundation to help secure
The wall to the foundation. In addition, they are also planning to add a concrete cap to the top of the wall, intended to help bind the wall sections together.

The pile of fine gravel

The pile of sifted clay soil

Bags of portland cement

       There are some serious advantages to rammed earth construction.  The completed building has an incredible thermal mass which tends to stay cooler in the summer.  It also is relatively inexpensive.  The major down side that I could see was a whole lot of serious manual labor.  Also, if you are building it without the benefit of heavy equipment it seems to take quite a bit of time. However, with the heavy equipment it goes much faster but isn't so inexpensive.

A completed section of wall

Tunnell family picture on the scaffolding