My Mother's House Part III
(Page 3 of 4)
November/December 1981
By the Mother Earth News staff
The expansive clay is also quite stable. It can be wetted and dried an indefinite number of times (after all, who knows how many such cycles the material has gone through In the last 150 million years?) . . . is unaffected by sunlight . . . and can be frozen, heated to over 400°F, or even exposed to ionizing radiation without losing its useful properties.
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The challenge that faced Dr. McGroarty—when he began to work with bentonite—was to develop agents that, when added to the material, would both help it stick to walls and keep it stable (that is, unexpanded without drying) for packaging and application. As a result of his research, Bentonize employs a patented mixture of organic resins (from soybeans, for example) and alcohol, which keeps it workable. The product is entirely nontoxic and requires a minimum of energy to produce.
Bentonize is available in either trowel—or spray—on form, but the hand-applied type is generally chosen by do-it-yourselfers. (Effective Building Products encourages owner-builders to apply their own waterproofing, and offers an excellent how—to booklet called The Bentonize System of Earth Sheltered Housing Water proofing—which describes the correct methods of using the firm's materials—for $5.00, plus 95¢ shipping and handling, through Mother's Bookshelf, P.O. Box 70, Hendersonville, North Carolina 28791.)
The gray mud is scooped from five-gallon buckets and applied like stucco (with a hawk and trowel) to a depth of about 3/16" (small imperfections can be overlooked, since the bentonite will expand to fill minor gaps). One bucket of Bentonize will cover about 60 square feet of wall, and will remain workable for approximately two hours after application.
Under Dr. McGroarty's supervision, our crew applied the waterproofing to the bermed walls of our house in less than a day, and we had to cover the clay quickly with a protective layer of polyethylene before a thunderstorm blew in. (If Bentonize is exposed to water before the backfilling is done, the material will expand and slough off the wall.)
The following morning we stuck expanded polystyrene insulation to the "mud blanket" . . . using dabs of fresh Bentonize as glue (the boards could have been applied directly to the waterproofing if we'd been prepared to backfill immediately). Though the insulative panels will add to the thermal efficiency of our house, their primary function is to protect the Bentonize from being damaged by rocks in the fill earth. Still, we used two inches of polystyrene instead of the standard one inch when coating the upper six feet of the waterproofing . . . in order to reduce the loss of heat to the cool (in the winter) top layers of dirt.
