Mechanizing Straw-Clay Production
By Alfred von Bachmayr
My first experience with light-clay straw was at a workshop in which the straw and clay had to be mixed by hand with pitchforks. I remember thinking that I loved the finished product but I discounted the viability of the material due to the high labor requirement.
Having grown up on a farm where my father was always creating machines out of items from the junk pile, my mind went to work on a mixing device that could be easily made out of materials obtainable anywhere. I first tried a conventional cement mixer but found it too small and awkward to process significant amounts of material. I then created a tumbler out of a 55-gallon (250-liter) drum, which replicated a cement mixer; even though the volume was greater, the problem of limited batch size remained. I started thinking about a rotating tube with the raw materials being fed in one end and the mixed product coming out the other.
After welding two 55-gallon (250-liter) drums together to form a tube, I attached a driving belt to turn the tube to an HP electric motor. The raw material was fed in the upper end of the tube in sequence (straw, water, and clay) and mixed as it tumbled down the tube. By adjusting its pitch, I could control the rate at which the materials went through the tube. A series of tines welded inside the tube helped mix the material more thoroughly by lifting it at each rotation up the side of the drum and dropping it when the tines approached vertical.
This device allows the ratio of clay to straw to be adjusted as desired. For walls where high insulation values are desired, the material can be mixed at a dry weight of approximately 35 pounds per cubic foot (560 kilograms per cubic meter). Where more mass is desired, a higher percentage of clay is used and the mix can be made to weigh 50 to 75 pounds per cubic foot (800 to 1,200 kilograms per cubic meter). To optimize the thermal performance of a building, the lighter mix is used in north and west walls, while the heavier mix is used on the south, east, and in interior walls.
My mixer design continues to evolve. In order to produce even more material, I developed a larger tumbler, 36 inches (90 centimeters) in diameter and 10 feet (3 meters) long. It is made of a tractor tire rim split in half, with corrugated metal roofing attached to create the tube. It is turned with a gear motor at about 30 revolutions per minute, and the whole device is mounted on a trailer that can be pulled to construction sites.
This large device can produce enough mixed light-clay to keep a large crew busy compacting it in forms. The next evolution will involve a more automated feeding of the raw materials to the rotating drum and better delivery of the mixed material to the walls for compaction.
Architect Alfred von Bachmayr ( 1948 – 2013)
By Catherine Wanek
My friend Alfred Von Bachmayr passed away from a rare cancer, August 4, 2013, at his home in Tesuque, NM. I miss him, and wish to honor his memory with a short tribute to his many contributions to human beings in need, and his cleverness as a natural builder.
Alfred von Bachmayr cared about people and the planet. An award-winning architect, he designed and built low-cost, energy-efficient, and sustainable buildings using straw bales, straw-clay, pumicecrete, adobe, earthen plasters, rainwater catchment, alternative waste disposal systems, and solar electricity. He also came up with low-tech ideas to make natural buildings easier, simpler, and more affordable. He invented the straw-clay tumbler described above and developed the “pallet truss”, a structural solution for supporting roofs where wood is scarce, and pallets are readily available.
Alfred grew up on a farm in Colorado, and graduated with a degree in Architecture from the University of Colorado in Boulder. He apprenticed with an architectural firm in Aspen, where he worked on an early passive solar house for Steve Martin (the comedian and bluegrass musician), and went on to design the award-winning passive solar dormitory at Fountain Valley School in Colorado. In the 1980’s he became involved with low-income housing and was a founder of the Affordable Housing Alliance in Boulder.
In the early 1990’s he moved to Tesuque, New Mexico, (near Santa Fe) where he designed and built his own innovative solar adobe home in a family compound. In addition to his private architectural practice, he worked with Habitat for Humanity designing a house for them that won a national award. During two years as the Director of Earthworks Institute, he led a project in Fiji involving low-cost structures using local and native materials. Alfred also designed and helped build (along with Matts Myhrman, Judy Knox and many others) a strawbale house for Mary Lowe, an 84-year-old great grandmother on the Zuni Pueblo.
Alfred was one of about 20 strawbale advocates (including Steve MacDonald, Joe Kennedy, Derek Roff and myself) who met at the Black Range Lodge in 1999 to discuss how we might use strawbale building knowledge to help during the war in Kosovo. We saw people being made homeless by bombs, and winter was coming. By the end of the day we founded Builders Without Borders, which was conceived as a network of ecological builders and other volunteers dedicated to teaching and promoting natural building as a solution to affordable, comfortable housing.
Through BWB, Alfred was integral in designing and building a strawbale Hogan with the National Indian Youth Leadership Project (NIYLP) near Laguna Pueblo, an eco compound for Catholic sisters in Chaparral, NM, and a strawbale house for a family whose house had burned down in Anapra, Mexico, a sprawl of pallet houses without city infrastructure, across the border from relatively prosperous El Paso, Texas.
The Anapra project evolved into a long-term relationship with the community, during which he founded World Hands Project to continue the work, forging a partnership with a local priest and developing relationships with local builders. Alfred listened more than talked, and developed designs that worked with locally-available building materials and skills. He located a nearby source of free clay to replace cement (which was unaffordable), and shifted from strawbale buildings to straw-clay infill inside pallet walls covered with pallet roofs, which were easier for local builders. He continued working in Anapra, an unincorporated suburb of Juarez, until the border drug wars made him feel that it was too potentially dangerous to bring his small team of volunteers into the region.
During the last decade he worked closer to home, consulting with the Picaris Pueblo on a greenhouse design, and helping with the nearby Tesuque Pueblo to design and build a strawbale Seed Bank, and develop their proposed Community Plan of 2013. He also helped restore an old adobe building into the Esperanza Shelter, a wonderful, warm space for kids from battered families. Alfred’s community service included many years as the Mayordomo of the Acequia (the neighborhood irrigation system) in Tesuque.
Alfred was also a superb athlete: A triathlete, a swimmer and a kayaker, he ran most of the big rivers in the West (doing the Colorado River through the Grand Canyon six times). He went as far as the Northwest Territories in Canada to run the Nahanni River. He won the Fourth Annual Kinetic Sculpture Challenge race in Boulder in May 1983, setting a course record.
Alfred was a creative tinkerer and a hard-working practical person. He loved people and nature, grew a bountiful garden, lived an active and joyful life, and had many friends. He will be remembered.