The soil for earthen structures should be a sandy loam, not expansive (which means that it won't swell and shrink to the point of cracking), with a low organic-matter content. The National Bureau of Standards (NBS), which ought to know about these things, recommends a mix of 17 percent clay, 25 percent silt, 19 percent coarse sand, and 42 percent fine sand. (Note: Those NBS folks may be real smart, but they sure can't add. Still, their advice makes sense as long as you adjust the numbers a little bit to come out to 100 percent. Don't exceed 100 percent; if you do, you may experience structural problems.) Straw is often added to the soil mixture to improve its strength. Water content should be around 10 percent (7 percent for rammed earth).
Use soil from your site if it can be taken without damaging the environment; soil can come from a spot where you'll be building a structure. Using on-site soil is the most sustainable way to go. Whatever the source, choose your soil carefully.
Waterproof the soil by mixing asphaltic emulsion (a bad petroleum-based product) at 4 percent by volume into the mud when making the bricks; they'll last a lot longer. You can also add portland cement (up to 6 percent of the total volume) to waterproof and strengthen the material. Keep in mind that these adulterants make the wall less recyclable. However, it will still have a much lower impact than a concrete block or other conventional wall.
It's a good idea to do a test block to be sure your soil mixture won't crack excessively. Adjust the clay/sand ratio of your soil if you have problems. Add clay if the soil is too crumbly and sand if it cracks too much.
Was this article helpful?
How would you like to save a ton of money and increase the value of your home by as much as thirty percent! If your homes landscape is designed properly it will be a source of enjoyment for your entire family, it will enhance your community and add to the resale value of your property. Landscape design involves much more than placing trees, shrubs and other plants on the property. It is an art which deals with conscious arrangement or organization of outdoor space for human satisfaction and enjoyment.