Pumice-crete

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Pumice-crete, a mixture of pumice and a little portland cement, has been used throughout the Southwest as a sturdy and insulative wall material.  Although it is less insulative than straw bale, it's weather resistance makes it a great choice for a stem wall under bales where water is more likely to penetrate.   Its relative light weight makes it easy and quick to mix and pour.  Great boots for a natural house!