Earth Block and Earthbag Testing

Full text of the video is available on my Naturalhouse’s YouTube channel. This blog post will focus on summarizing the test results. Please note that even though half the samples were earthen blocks, you can do these same tests on earthbags to help develop a good soil mix. A link to additional tests can be found at end of this blog post. Also note, although I say “clay” for brevity it’s actually clay soil not pure clay that’s used in all these tests.

Earth Block and Earthbag Testing Results (click to enlarge)
Earth Block and Earthbag Testing Results (click to enlarge)

The strongest sample turned out to be the earthbag made with vetiver, clay soil and rice hulls. This sample not only passed every test, including zero damage in the drop test, it also had a distinctly different feel than the others. It made a ringing sound when it was dropped that reminded me of clay brick. The sample was lighter weight due to the hulls, and, of course, would have improved insulation value. It probably gained strength from compaction and the long vetiver fibers.

Adding rice hulls to adobe and other forms of earthen construction is an ancient process that begs further research. For instance, I just learned rice hull/clay was the traditional method for building houses in Taiwan, and now the high cost of energy for air conditioning in Taiwan is creating renewed interest in this ancient technique. (No air conditioning needed in a properly designed adobe or earthbag house.) Note the similarity with straw/clay that has proven a huge success in Europe for centuries.

For additional soil tests, please refer to Patti Stouter’s excellent soil testing guide Soil Tests for Earthbag.

2 thoughts on “Earth Block and Earthbag Testing”

  1. Great to see some performance information, even when done in an informal way. It would be helpful to have an idea of the proportions of fiber and earth in the different blocks. And it would be helpful to have some information about the clay used- how it performed in some sort of ribbon test and hardness test.
    Owen: Please refer to my YouTube videos that show the exact proportions and techniques. The clay soil is the same material used to make CEBs. We also used it for our earthen plaster. Works great for everything.

    Last on my probably impossible list is to hear how much extra time these different materials took to mix and place in bags. Even a guess at this point can be helpful. The mesh tubes and bags will throw earthbag wide open for adding fibers if the mixing can be done in an efficient way.
    Owen: Fiber isn’t needed in earthbags in most cases. Adding fiber is one more step that will slow you down, and so I wouldn’t use it unless there’s an important reason. One option is to use straw that’s already been cut short so you don’t to cut it manually. Straw bale builders prefer long straw, but some machinery cuts it short — about 5″-8″.

    Fiber in clay blocks can be important for insulation in many climates. But often damper clay is used when combining fibers. Did any of these seem lighter when formed than ordinary subsoil earthbags?
    Owen: Yes, the fiber blocks are slightly lighter weight. But to really make a noticeable difference I made samples with extra vetiver, but unfortunately they didn’t pass the drop test. But keep in mind they had been sitting around for about 5-6 months. They’re the same samples used in the termite test.


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