Sometimes old techniques are being rediscovered and their value proves to be effective in modern times too. This applies also to the technique of building with sand- or earth bags. This technique is both old and new.
Sandbags have long been used, particularly by the military for creating strong, protective barriers, or for flood control in extreme weather conditions. The reasons that make them useful for the named applications are also relevant for the building process of houses. With this technique massive and substantial walls can be created that can resist all kinds of severe weather conditions (or even bullets and bombs). The buildings and houses can be erected quite easy and quickly with components that are already available in nature. Potato or grain bags were traditionally used for this purpose. But they only work fine until they eventually rot. Newer polypropylene bags have superior strength and durability, as long as they are kept away from too much sunlight. For housing purposes the bags should be covered with some kind of plaster for protection.
There has been a new interest in earthbag building since architect Nader Khalili, of the Cal-Earth Institute, began experimenting with bags containing adobe soil as building blocks for creating structures like domes, vaults and arches. Mr Khalili was already familiar with Middle Eastern architecture and the use of adobe bricks in building, so he could imagine building in this way. The Cal-Earth Institute has been training people with the particular techniques.
Earthbag construction is an inexpensive method to create structures which are both strong and can be quickly built. It is a natural building technique that evolved from historic military bunker construction techniques and temporary flood-control dike building methods. The technique requires very basic construction materials: sacks, filled with inorganic material usually available on site or in the near surroundings. Standard earth bag fill material has internal stability. Either moist subsoil that contains enough clay to become cohesive when tamped, or an angular gravel or crushed volcanic rock is used. Walls are gradually built up by laying the bags in courses — forming a strong staggered pattern similar to bricklaying.
The walls can be curved or straight, domed with earth or topped with conventional roofs. Curved walls provide a surprisingly good lateral stability, forming round rooms and/ or domed ceilings like an igloo. Buildings with straight walls longer than 5 m (16.4 ft) in length need either intersecting walls or bracing buttresses or piers added. International standards exist for bracing wall size and spacing for earthen construction in different types of seismic risk areas. The most notable standards are the performance-based standards of New Zealand.
To improve both friction between each row of bags and finished wall tensile strength, barbed wire is often placed between the courses. Twine is also sometimes wrapped around the bags to tie one course to the next, serving to hold the in-progress structure together and add strength. Rebar can easily be hammered into walls to strengthen corners and opening edges and provide more resistance against overturning.
The structure is typically finished with plaster, stucco or adobe both to shed water and to prevent any degradation of the used materials from solar radiation. This construction technique can be used for emergency shelters, temporary or permanent housing and barns. It is frequently chosen for many small-to-medium-sized institutional structures in the developing world.
This building technique is a very good option to create strong and cheap buildings in the developing world but also in developed countries.