After a hands-on workshop taught by architect Nader Khalili, we returned home inspired to build our first earthbag project. We started with simple, linear, buttressed exterior walls, graduated to serpentine garden walls, progressed to a small dome and are now finishing a larger dome with a vaulted entry way and big sunny arched windows. This last project turned into a casual workshop inviting people to learn "Flexible Form Rammed Earth," A term we now use that we feel best describes this construction method.
"Flexible Form Rammed Earth (F.F.R.E.)" is a free-form version of rammed earth construction. Since the bags act as a flexible form, it allows the architectural design of curvaceous, sensual structures. We have the ability to mold, bend, writhe and swoop sculptural forms inspired by nature's artistic freedom, while providing structural integrity. Hence, a whole house from foundation to walls to roof can be built using the "Flexible Form Rammed Earth" technique.
Our personal education began when we adopted the FQSS stamp of approval - Fun, Quick, Simple and Solid! By following this criteria, we made the ease of the construction process our priority. As long as the work was Fun and Simple, it went Quickly and the results were Solid. When the work became in any way awkward, FQSS deteriorated into Frustrating, Quarrelsome, Slow and Stupid, prompting us to stop, change tactics or blow the whole thing off and have lunch. (Returning refreshed often spontaneously resolved the problem, resuming FQSS approval.)
THE BASIC PROCEDURE is simple. The bags or tubes are filled with a suitable pre-moistened dirt right on the foundation, laid in a mason-style "running bond." We use #10 coffee cans for scooping and filling. This eliminates any heavy lifting. After a row of bags has been laid, the row is compacted with hand tampers. We lay two strands of long-barbed 4-point barbed wire between every course which acts as a "Velcro mortar" cinching the bags in place. This also provides tensile strength while allowing for the rows to be stepped in to create self-supporting corbelled domes and other unusual shapes. Round structures are guided by the use of a revolving compass. Arched openings are incorporated with the use of removable plywood forms until the "keystone" bags are tamped into place.
An average of four people working 5-6 hours per day moved 40 tons of earth with coffee cans to complete the "bag work" of the Honey House, a 16-ft corbelled dome, in 19 days. In another 7 days, we moved 7 tons more in the form of cob onto the roof.
The material we used in our bags is called "reject sand," obtainable from most gravel yards. Reject sand is the by-product of the process that separates sand and "clay fines" from the gravel being produced at these facilities. This reject material often has the best ratio of clay to sand (approximately 25% clay to 75% sand) for rammed earth construction. And... it is dirt cheap! We paid $1.00 per ton plus delivery.
The bags we used for our construction are woven polypropylene "misprints." The companies that manufacture these bags sometimes have imperfections or mistakes in the printing process that render them unsuitable to their clients. Rather than throw these bags away, the manufacturers will sell them at a reduced cost. A comprehensive list of bag manufacturers can be found in the Thomas Register at your local library. Our favorite manufacturer has been Cady Industries in East Memphis, TN. (Now Inpack)
Exterior and interior finishes of these structures are open to many options suitable to the climate and design of the building. Wall plasters range from a variety of natural adobe to stabilized earth to lime/cement stucco. Since a corbelled F.F.R.E. roof is exceptionally strong they can easily be bermed into a hillside, or carry the weight of a 9-inch-thick living roof, or a hefty layer of sculpted adobe. Terra cotta tiles, mortared slab stone or slate shingles as well as wood or asphalt shingles are also suitable roofing materials. In warm, frost- free climates, lime/cement stucco can be appropriate.
Thermal performance of earthen structures offer a level of comfort expressed by a long history of world-wide experience. 50% of the current world population live in earthen dwellings from climates as diverse as China, Australia, Africa, Europe, and throughout the US. Dense materials such as adobe, and rammed earth have R- values roughly equivalent to 0.25 per inch... yet despite this low R-value, earthen walls function as an absorbent mass that is able to store warmth and return it to the living spaces as it is needed. This has been documented as the thermal flywheel effect and is referred to as the K-value. This substantiates the common experience people feel that an adobe house is "warm in the winter and cool in the summer."
The merits of "Flexible Form Rammed Earth" are in its use of cost-effective materials, simple construction methods and the durable resistance to the ravages of fires, hurricanes, flooding, termites and, as Nader Khalili has proven in Southern California, earthquakes. This makes this type of architecture capable of surviving as long as its 500-1000 year old rammed earth relatives around the world.
Costs for do-it-ourselves construction of the Honey House before windows and doors:
|Home made tools (compass, stands, pounders, etc.)
|Plywood arch forms (reusable)
|Professional backhoe excavation
(2ft. deep x 16ft. diam.)
|Straw for plaster/cob (20 bales)
|4-point barbed wire (2 rolls)
|40 tons reject sand (delivered)
|1000 bags (delivered)
* Tools of the the "dirt bag" trade. To comply with the FQSS theory, we adopted techniques and developed a few specialized tools that enhanced the precision and quality of the construction, Equipped with the latest tools of the "dirt bag trade" a new jargon of bag talk has been born: bag stands, sliders, diddling, tube chutes, full pounders, quarter pounders, sliding compass, fans, halos, chicken-wire cradles, can tossing, contouring, hard-ass bags, and a huge breakthrough in bag technology, "scooching." These simple additions to the repertoire of FFRE construction have turned an awesome job into a friendly task.