An alternative house building material that we haven't talked about before is rammed earth. And, yes, it's exactly what it sounds like. The walls are made from earth that is smashed into forms.
Rammed earth has a long history around the world and was popular in the United States before railroads made the transportation of lumber and other building materials commonplace. In recent years, the material has been seeing a resurgence as an eco-friendly option for home building. It doesn't get much more natural than building a home right out of the ground around it!
How Building a Rammed Earth House Works
The building process starts out with a concrete foundation that protrudes above grade six to eight inches as a "stem wall." The rammed earth wall will stick to the stem wall via gravity and pressure.
Mineral-laden soil (not topsoil--save that for the garden) is used for the walls. A mixture of mostly sand with some clay works well. On sight soil often isn't of the right consistency, so you may have to get it from a local quarry (this saves the problem of correcting gaping holes in your landscape anyway).
Typically 3-10% portland cement is mixed into the soil for stabilization. The mixture is then moistened to lubricate the soil particles and help with compaction.
The earth is placed into box-like ramming forms (similar to forms used for creating concrete panels), which are attached to the stem walls. The wall depths will be anywhere from 18 to 36 inches (in a two-story building the first-story walls are typically wider). Plumbing and electrical are usually run within the forms, and windows and doors are framed out before the earth is rammed home.
In the end, the rammed earth walls will have a slightly textured surface and striations left from the ramming process. Wall color depends on soil mixture. You can, of course, paint but many homeowners want to be able to see and admire their natural rammed earth walls and will simply apply a clear sealant to interior walls to prevent flaking. In cold climates, foam insulation is often added to exterior walls, which are then covered with stucco.
Rammed earth houses are a unique and eco-friendly way to build a home.
Source: Living Homes: Sustainable Architecture and Design
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