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Earthbag building

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Earthbag tubes being used to build vertical walls. By Gabriel Anast from Gallup, US (Tube walls) CC BY-SA 2.0 (http://creativecommons.org/licenses/by-sa/2.0), via Wikimedia Commons
Cal-Earth polypropylene tubes being used to construct domed structures. By DVIDSHUB CC BY 2.0 (http://creativecommons.org/licenses/by/2.0), via Wikimedia Commons

History[edit]

The notion of building walls with sandbags or earthbags has been around at least 100 years.[1] Originally and into modern times these have tended to be burlap (hessian) fabric bags forming temporary structures acting as flood barriers or as military fortifications. It is unclear exactly when the first time this was done,[2] but there is some evidence that in military settings sandbag walls were being used prior to World War I. Indeed, some WWI trenches reinforced with oil impregnated sacks still survive, despite being intended to be temporary.[2]

Building permanent structures such as homes using earthbags is a more recent development.[1] Otto Frei experimented with earthbag building in the in 1960s in Germany.[3] In the 1970s, again in Germany, Gernot Minke and others at the Research Laboratory for Experimental Building at Kassel Polytechnic College were investigating ways of building earthquake resistant structures without cement. They used polyester and burlap tubes filled with pumice to make domed structures. With the Francisco Marroquin University in Guatemala and the Centro de Estudios Mesoamericano Sobre Tecnologia Apropiada (CEMAT) a structure was built in Guatemala in 1978 out of lime soaked cotton fabric bags filled with pumice sand.[4]

The Earthbag building method was popularized by Persian Architect Nader Khalili who eventually developed a building technique he termed Superadobe, where polypropylene bags or tubes filled with moistened adobe soil were used to form often domed structures. Khalili went on to publish 6 books and found the non profit organization Cal-Earth Institute (California Institute of Earth Architecture) in 1981.[5] He has been criticized for claiming his superadobe technique was "freely put at the service of humanity and the environment" at the same time as attempting to patent earthbag building techniques in very general terms in 1991. It is claimed he requested that all other promoters of earthbag building enter into a contract with him to continue their work.[1]

Terminology[edit]

Contained earth is the basic technique of filling containers with earth. Modular contained earth is the use of bags or tubes in walls which rely on rebar and/or strands of barbed wire between courses to keep the form of the wall. Flexible form rammed earth is another term that has been used.[3] Solid contained earth is a more accurate term for hyperadobe, developed by Fernando Pacheco of EcoOca in Brazil. A pliable knit raschel mesh tube is used, the same material used in packaging fruit. This mesh allows the earthen fill to solidify between courses as long as the fill is built damp. Solid contained earth has higher shear and out of plane strength than modular contained earth of the same soil, and may allow the use of wire mesh in addition to or in place of barbed wire.

Contained Sand uses sand fill or any fill too dry or with poor cohesion that performs structurally like sand bags. Such bags must be solid-weave fabric have good protection from fabric damage. Contained sand needs more vertical reinforcement than contained earth. Structurally, alternative loose fills (like rice hulls) will create a wall more similar to contained sand than to contained earth.

Contained Gravel uses fill of any aggregate larger than coarse sand. Contained gravel can function as concurrent footing and footing drain material, and can use either solid-weave or mesh containment.

Containers[edit]

The basic vessel for contained earth building may be either numerous bags/sacks which are used as individual bricks, or long tubes which become the entire course in a wall. A common size for individual bags is 18 inches by 30 inches when empty (45*76 cm).[2] The fabric used in bags or tubes may be a solid weave or a mesh.

Polypropylene[edit]

Polypropylene (also termed polypropene) is the second most commonly produced plastic in the world. Long rolls of polypropylene tubing are available from manufacturers. These large rolls of tubing are normally intended to be cut and stitched into individual bags and then used as rice bags, etc. Solid weave Polypropylene bags or tubes are the most popular type of container in earthbag building.

Polypropylene is cheap, durable, resistant to rot, water damage and insects. A study reported that polypropylene fabrics may have a half life of 500+ years in benign environments.[6] The tensile strength of such bags is higher than steel,[6] and they are resistant to circumferential forces produced by load bearing.[6] Polypropylene is vulnerable to ultraviolet damage and therefore is left covered from the Sun during construction and plastered once the structure is finished. Polypropylene fabrics may be stabilized/treated are intended to have greater UV resistance, but this may equate to a few months extra survivability in sunlight at best.

Burlap[edit]

Burlap sacks are sometimes used, being seen by some as a more organic, "natural" material.[2] However, burlap sacks are often treated with hydrocarbon mold inhibitors which can cause allergic reactions in some individuals.[7] Burlap sacks are not as durable,[2] and are vulnerable to rot.[8] Burlap sacks can be more expensive relative to polypropylene.[2]

Mesh[edit]

Mesh tubes have also been used, for example, the hyperadobe technique.

Filler material[edit]

The nature of the fill material determines the structural and thermal properties of the wall. For example different fill materials may provide thermal mass effect (dense fill materials) or insulation (porous, air filled materials).[8] Earthbags containing gravel may also act as non-wicking, partially insulated foundations.[8]

As a general rule the weaker the fill material, the stronger the fabric of the container must be.[2] For instance, a hard setting filler such as adobe relies little on the containers. Once adobe is fully set, the containers could be removed without any reduction in structural integrity.[2] Conversely a very fine material such as dry sand relies entirely on the long term strength of the material used to contain it.[2]

The make up of soil can be assessed without special equipment via simple tests such as the drop test and the roll test.[6]

Adobe[edit]

The superadobe and hyperadobe methods utilize adobe earth as a fill material. With regards superadobe, the contents of the bags settles into its permanent form within 3 days.

Earth[edit]

Most types of subsoil are acceptable for use in earthbag construction and a precise ratio is not required.[7][6] A typical ratio is 25-30% clay, 70-75% sandy soil, 10% moisture.[7][6] Clay is required to bind aggregates together.[7] A mix with over 30% clay may be unstable,[3] and must be kept dry to handle and may slump if it becomes too moist.[6] High clay content soil is also harder to dig and to fill into bags.[7]

The Materials[edit]

  • Containers (i.e. Bags or tubes)
  • Filler material (usually earth)
  • Barbed Wire (4 point galvanized)

The Tools[edit]

File:Tools for Earthbag.jpg
Earthbag can be built with basic hand tools
  • Shovels
  • Tamping tool
  • Bricks/weights
  • Nails/wire
  • Buckets
  • Hose
  • Sheetmetal Slider
  • Pliers
  • Ladder
  • leveling board
  • Hoes
  • Rubber mallets

Procedure[edit]

Foundations[edit]

References[edit]

Further reading[edit]

Books

Websites

Videos