Vetiver/Clay Follow-up Report

Long vetiver fibers hold the soil together and increase shear strength.
Long vetiver fibers hold the soil together and increase shear strength.

I’m real happy with how the sample vetiver/clay block and earthbag turned out. This follow-up report summarizes some of the pros and cons. You can read the first report here.

The block dried in a few days, but the mix in the bag was slow drying (it took about 2-3 times longer to dry) and so there is a risk of mold developing when building thick walls in humid climates.

Making vetiver/clay is rather time consuming. It takes about twice as long as filling and tamping typical earthbags. In terms of time and labor it’s about double — it’s like making adobes and then also building the wall later. The most practical application may be interior walls using vetiver/clay blocks or using vetiver/clay as stuffing in pallet walls or slip-form construction.

I got the idea for experimenting with vetiver/clay after hearing it was used to build a silo for storing rice. This fascinating report contains the following gems of wisdom.

“For constructing the wall, vetiver grass and clay must be prepared. From our study, only fresh vetiver grass should be used and this must be dried for four to five days to reduce the water content to less than 10 percent and to prevent insects and fungi fertilization. The clay used for the fabrication of the vetiver-clay bundles must be cohesive and must have high plasticity. It should be fine, smooth and uniform, and free from impurities such as broken tiles, roots, twigs, or other organic matter. The clay should be sun-dried for at least four to five days to reduce its water content to less than five percent. Then, the sun-dried clay would be soaked in water at the ratio 2:1 (clay:water) for twenty-four hours and mixed manually until a uniform slurry is formed…”

Termite resistance: I put the samples on a mound of decaying wood that’s infested with termites for five months. There was no termite damage even though we didn’t prepare the vetiver as recommended in the above report. But I recommend following their advice since they tested it much more thoroughly.

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