by Athena and Bill Steen - Cohabitat

Depending on site conditions, a well constructed
earthen floor may consist of several layers.
Preparing the Base
To help prevent the floor from cracking or settling, the ground
should be well compacted an free of all movement All organic and
plant matter should be removed. If very expansive clay is present, it
should be removed and replaced with another non-expansive soil or
other substitute. The ground should also be dry before beginning
construction of the floor
Waterproofing and drainage
If the capillary rise of moisture is a problem, steps need to be
taken to improve drainage and stop the upward movement of moisture.
For many situations, a layer of 6 to 12 inches (15 to 25 cm), of either
dry stone topped with gravel, gravel, or coarse sand may be adequate
to improve drainage and stop moisture migration. Certain volcanic
stones like pumice could also provide the additional benefit of
insulation as well as protection from moisture. The uppermost portion
can be comprised of finer gravel or coarse sand to prevent the upper
layers of the floor from falling through.
If more drastic measures are required, plastic or petroleum based
membranes can be laid down, to prevent capillary rise, but at the cost
of losing the b readability ofthe floor and contact with the earth itself
Preferably, this membrane should be laid with care on top of a layer
of sand to avoid any tears or punctures.
If a non-synthetic, water-tight barrier is desired, a thin layer
( 1/4" to 3") of soil with a high clay content or bentonite can be used.
It can be applied in a moist state in several layers, filling all cracks as
each layer dries. Troweling each layer will help compact the clay
mix and reduce the pore space. This will further aid in creating a
water-tight seal. The top layer in particular needs to be wellcompacted.
Bentonite sheets (1/4 H
thick, backed with cardboard), can
also be purchased, although more costly. (See resources.)
It might be possible that the application of a lime plaster which has
been stabilized with a water-resistant material, like prickly pear cactus
gel, could be effective as an anti-capillary barrier Whatever approach
is used, it should be tested first to determine if it performs well.