Bag and Fill Materials

As can be assumed by its name, there are two important things to consider when choosing Earthbag construction.

THE EARTH

Common Materials

Essentially any type of soil can be used, but knowing the makeup of soil can help achieve the best mix. Soil is made up of clay, silt, sand and gravel. Silt is extremely fine-grained, and using too much in an Earthbag structure will weaken it. Gravel, or jagged pieces of rock, is sometimes used at a foundation level in Earthbags, however most commonly used is a mixture of clay and sand. Clay serves as the glue to hold sand together, while the loose particles of sand form the majority of the Earthwall’s stability. Earthbag builders recommend a ratio of 70 percent sand to 30 percent clay due to the clay shrinking when dry and expanding when wet.

Alternative Materials

Soil: 

Found on almost any site, soil provides a cheap and easy method of constructing Earthbags. Moistened material will also compact much more effectively creating a more stable structure. Recommended is 10% moisture content in the soil. (Soil with about 10% moisture will form a ball in your hand, but shatter if dropped)


Rice Hulls:

Often discarded and thought of as a pure waste, rice hulls start their life protecting grains of rice as they grow in the field. As it turns out, these hard shells can now be used to protect the interiors of our buildings by forming structural walls with impressive fire resistance and insulation properties. They are also resistant to moisture which eliminates insects, rodents, mold, mildew, or fungus. Typically a rice hull filled earthbag will weigh one tenth of a soil filled earthbag.

Scoria (Volcanic Rock): 

Scoria is perfect for super insulated earthbag walls.  It's low cost, all natural, rot proof, fireproof, doesn't attract pests, is lightweight and easy to work with.


Perlite: 

Perlite is a generic term for naturally occuring siliceous rock that's been heated and expanded.  It can expand 4 to 20 times its original volume.  The tiny air spaces provide excellent insulation.  Perlite is a form of natural glass and is classified as chemically inert making it perfect for Earthbag building.  Perlite however can be more expensive than other materials.

Stabilisation of Organic Material

Although the above materials are suitable for most walls, there are instances where stronger, more rigid earthbags are required, such as lintels over windows and doors. If the fill material is too fine it will not compact into a solid effectively enough in certain areas. Other elements can be added such as lime or cement which allow the fine material to bond together creating a much more rigid and firm structure.

THE BAG

Typically weighing 23-45kg, Earthbags are made of either polypropylene or burlap. Although Burlap is a cheaper and more natural material, it is less durable than polypropylene. Generally, the weaker the fill material, the stronger the bag should be.

Bag size can vary, depending on manufacturer and builder preference, but the most common size for housing construction is approximately 457 mm wide and 762 mm long (usually specified as 18”x 30”).. This size has been accepted by the Earthbag community as having an optimal balance of strength and workability, based on construction experience. Bags are also available in larger dimensions such as 508 mm x 914 mm and 635 mm x 1016 mm.