Compressed Earth Blocks
Light Straw-Clay (Leichtlehm)
Hemp and other Fibers
Natural Plasters and Finishes
Recycled Building Materials
Straw Bale Construction
Wattle and Daub
Adobes are sun-dried mud bricks stacked with a mud mortar to create thick-walled structures. Their use dates back centuries in traditional earthbuilding areas such as North Africa, the Middle East, South America and the southwestern United States, where in all cases this building method is still in widespread use. Dramatic examples of vaulted and domed structures built entirely of earth still stand after centuries in the Middle East, testament to adobe's timeless beauty and structural integrity.
While in the "South" its use is mostly confined to those too poor to have access to other building materials, in the southwest U.S., adobe is often used by the very rich, illustrating its wide appeal. Adobe is appropriate in areas which are labor-rich and capital-poor, because it is so labor intensive, using local materials and simple tools.
Adobe bricks are made with a completely saturated mixture of clay and sand (and sometimes straw or manure), poured or pressed into forms, which are then removed. After the bricks have dried for several days, they are turned on edge for further drying, then stacked for transport or for use on site. The adobes are laid on an appropriate foundation (usually stone or concrete) using typical masonry techniques with thick joints to take up the difference in size of the adobes. Typically, mud mortar is used, but a concrete- or lime-based mortar has also been employed in certain cases. Various stabilizers for the adobes themselves have been developed, with most, however, relying on cementitious or asphalt-based compounds.
While adobe is widely appropriate, certain precautions must be taken to ensure the durability of construction. Wide eaves are often appropriate to protect the walls from rain, and foundations must protect the walls from splashing. Mud plaster is traditionally used to finish adobe structures with minimal or no overhang of the roof, requiring replenishment every few years.
Cement stucco has also been used in an effort to provide longer lasting coatings, but in many cases has proven to be destructive, as the brittle stucco can crack, letting in water which dissolves the underlying adobes. Because the stucco can hide this damage, buildings can collapse before anything is sensed to be wrong. In addition, indoor moisture cannot escape, building up on the inside of cement stucco, eroding the wall. Because of this, there has been a return to favor of traditional plasters using mud, straw and other natural materials (see Natural Plasters and Finishes.)
Many building codes place severe restrictions on adobe construction, essentially limiting it (and other earth-based building technologies) to the desert southwest.
Bamboo is a species of plant in the grass family. It grows very quickly, providing renewable material for building, tools, and utensils as well as edible shoots. Common in the tropics, many species of bamboo grow in temperate climates as well. Strong and beautiful, bamboo has seen a recent resurgence in popularity with builders.
Bamboo as a building material is not commonly known in North America because of limitations on the import of living plants, and lack of knowledge of traditional techniques. This ignorance is beginning to change, however, as timber prices rapidly escalate, and western builders become aware of innovative uses of bamboo that have originated in Asia, Central America and South America.
Utilized for millenia in these countries, bamboo can replace wood and steel in many applications. It can replace rebar in concrete, as pins in straw bale construction, to create trusses and other structural members, as decorative elements, and has even been used as plumbing.
Its widespread use in tropical areas, as well as unsustainable harvest for export, can have its dangers: indiscriminate cropping can decimate stands and endanger interdependent ecosystems. To address this danger, an effort to create sustainable growing programs similar to those for tropical hardwoods is currently in development.
Cob is an ancient technique of building monolithic walls using "cobs" of moist earth and straw. It is being rediscovered as a multifaceted building material applicable to a number of conditions. Virtually forgotten in North America, cob was popularly reintroduced by Welsh architect and builder Ianto Evans, who inspired intense public interest in his self-built cob home created for under $500. A sculptural technique which lends itself to curved organic shapes, cob requires minimal tools and can be built by young and old alike.
The process of building with cob entails mixing local earth with sand and/or clay (depending on the composition of the base earth) and straw or other fibrous materials to create a stiff mud which is formed into small loaves (cobs). These cobs are then mashed together to form a monolithic wall on top of a stone or concrete foundation.
The relatively thick walls (they have been known to be up to six feet thick) proceed in layers or "perches" averaging 18" high before slumping occurs. After a period of time to let each layer solidify, work can continue. Irregularities can be shaved off with a spade or other sharp tool as work progresses.
A particular favorite of natural builders for its ease, sculptural qualities, strength, and thermal mass, cob is also useful in combination with other techniques. Windows and other details are "cobbed" into place, and niches and reliefs are easy to create. While extremely economical for owner-builders, cob is very labor intensive and time consuming, with walls taking up to a year to fully cure. In addition, the curving architecture is not to all tastes.
Cob has been used mostly in informal or experimental buildings in the U.S. while code testing procedures are investigated. Cob construction is undergoing a revival in England as well, where proponents are rediscovering five hundred year old houses in perfect condition.
Compressed Earth Blocks
Compressed earth blocks are similar to adobes, with the main differences being they are not fully saturated with water, are more dense than adobes, and are usually significantly more uniform. These blocks are created using a variety of machines. Some, like the Cinva-Ram invented in South America, use human labor and are relatively inexpensive. Expensive fuel-powered machines, on the other hand, can produce thousands of bricks in a day.
Because of their uniformity, compressed earth blocks need little mortar, and can even be dry-stacked. This uniformity also speeds up the laying process and results in straighter walls. A house was built several years ago by CRATerre, a French earthbuilding education and research group, in a total of 24 hours using compressed earth blocks.
More recently, an inexpensive, innovative machine has been invented in Auroville, India, which can make a wide variety of sophisticated block shapes using human power. This machine was demonstrated at the UN Habitat II conference in Istanbul in 1996, where a domed prototype house was built in a week by volunteers and local labor.
Earthbags are soil-filled fabric sacks or tubes used to create walls and domes. Traditionally used for flood control and by armies to create bunkers, this method of construction has been recently turned to a variety of natural construction purposes. The technique has been used by Gernot Minke of Germany, and is currently being pioneered in the U.S. by Persian architect Nader Khalili of the California Institute of Earth Art and Architecture (Cal Earth).
The use of earthbags is still in its infancy, but holds much promise as a quick, easy and forgiving technique which uses minimally processed soil and few tools. To build with this technique, moistened soil is placed into a bag set in place on the wall, the bag is lowered into place, then compressed using a hand tamper.
Heavy earth mixtures can be used with weaker burlap bags as the compressed soil makes the bags redundant once it sets. Stronger, structural polypropylene bags are preferable for sandy soils. Recycled sacks are often available free or at minimal cost. In earthquake prone areas, a layer of long-point barbed wire is used as "mortar" between the bags to contain slipping. Domes using these materials are easily achieved with a corbelling system utilizing long tubes made of the polypropylene bag material.
Numerous natural builders have taken to using the bags as simple foundations for straw bale or cob structures, or for simple site walls. Recent projects in Mexico and Nova Scotia have used gravel-filled bags as foundations for straw-bale walls to minimize rising damp.
Disadvantages with earthbag construction are that resulting structures may seem excessively "organic" to some and also require quite of lot of plaster in order to create smooth walls. Advantages of this technique include the opportunity to build in wet conditions and in sites prone to flooding. Cheap and easily transported, the bags could also be used for disaster relief housing. Successful ICBO-approved testing has been undertaken by Cal-Earth, and a code-approved public project was undertaken in Hesperia, California.
The use of tamped or poured earth mixtures to create floors is currently undergoing a renaissance in the southwest U.S. Methods range from the African use of fresh cow dung sealed with ox blood, to sealed earth mixtures.The technique involves pouring or tamping one or several layers of an earth mixture over a substrate of gravel, pumice or sand (a sublayer of straw-clay has also been used by builder Robert Laporte for insulation). Hardening agents such as blood, lime, cement or glue may be added. This mixture is allowed to dry and any cracks are filled with more mud mixture. Cracking can be allowed to occur at random, resulting in a flagstone-like pattern, or can be controlled by incising the floor to create a tile-like effect. When the floor is entirely dry, it is sealed, most commonly with successive applications of linseed oil and turpentine. The floor is often coated with wax to protect the surface.
Minor disadvantages of this system are its relative damageability and need for maintenance. It can also be time consuming to install because of long drying times. Advantages include its aesthetic values, softness to the feet, and reliance on cheap, often free local materials.
"Earthships" are the name for the independent living structures utilizing passive solar design and recycled materials developed by Michael Reynolds of Solar Survival Architecture. While not exclusively reliant on "natural" materials, earthships replace some conventional materials with recycled trash which is found scattered all over the planet.
Earthships are a system rather than a technique: typically, earthships are dug into south facing hillsides; soil-filled tires are then stacked like giant bricks to form side and interior walls providing a source of thermal mass. Old bottles and cans are used to create a variety of detail features and to fill in gaps between tires. The building is framed in wood on the south side and roofed with metal to collect rain water. Other systems include integrated wastewater treatment, photovoltaic electrical systems, solar hot water and passive solar heating.
Advantages of the system include self-sufficiency in all aspects, the use of recycled materials and local soil, and technical and aesthetic sophistication. Disadvantages include the complexity of building such a structure and the amount of labor required which makes it out of reach for many owner-builders.
The earthship concept has become a well-known and popular building system, especially in northern New Mexico. Several earthship communities have been built, and the system has received widespread media attention. Other builders have used the stacked tire concept to build houses which don't contain all of the systems of Reynold's designs.
Hybrid building techniques are a fascinating outgrowth of the efforts of a few visionary natural builders and the sharing of ideas in the natural building colloquia. The basic concept is that several techniques can be combined for increased building efficiency or unique artistic effect.
An example is to combine a thermal mass technique such as cob or rammed earth on the south side of a house, with an insulative system such as straw bales or straw-clay on the north side, taking advantage of the best qualities of each system. New solutions to common problems have begun to evolve from such creative combinations.
A disadvantage of this approach is the lack of practitioners with wide experience in a number of techniques, pointing to the need for increased communication and sharing of ideas, and the elimination of dogmatic insistence on the preference of one system over another.
Light Straw-Clay (Leichtlehm)
Leichtlehm (literally "light-loam") is a German technique of ramming loose straw coated with a clay slip into forms as an infill for timber frame structures. This technique has been popularly reintroduced to North America by Robert Laporte who teaches natural building courses nationwide. He has been joined recently by Frank Andresen, a builder with extensive natural building experience in his native Germany.
The technique consists of surrounding a frame structure with a thick infill of the straw-clay mixture. The frame is usually fully expressed on the interior of the building to take advantage of the beauty of the timber frame joinery. A lighter frame of wood is built on the eventual outside face of the building as an anchoring system for the straw-clay walls.
Loose straw and a clay slurry are tossed with pitchforks or mixed mechanically, then allowed to age for up to several days in order to allow the straw to absorb the extra moisture and thus create a stickier and more easily tamped mixture. For higher insulation values less clay can be used. Slip forms are set up between the framing members, and the straw clay mixture is tamped by hand in two-foot layers.
Occasional horizontal members spanning between the exterior frame are placed in order to "lock in" the straw-clay mass. Frank Andresen places the ends of these horizontal members at the upper ends of vertical slots in the frame in order to allow for shrinkage of the straw-clay as it dries. Once each layer is complete, the slip form is moved up and the next layer is tamped until the wall is complete. The walls are allowed to dry before final plastering occurs. Any shrinkage is taken up by stuffing more of the mixture into the cracks.
Robert Laporte commonly uses straw-clay stuffed loose between rafters as insulation, with the clay discouraging pests. He has also used it as an insulating layer underneath earthen floors. Frank Anderson has demonstrated a system of straw-clay tiles which can be placed between roof rafters as insulation and as a plastering surface. He's also introduced straw-clay bricks that can be used like lightweight adobes.
A variant on the straw-clay technique utilizes wood chips mixed with clay; the resulting mixture is poured into removable or sacrificial forms. This technique can also be used to create lightweight bricks.
Highly accurate buildings are possible with the timber frame and straw-clay technique, allowing a "natural" structure which compares in looks to conventional stick-frame housing, making it an appealing option for some homeowners. Some disadvantages of the technique include its highly labor intensive nature, and the long drying time. The straight walls achievable with this method, however, are desired by builders in southern countries who seek a western look in their houses, and to whom an "organic" structure is "old-fashioned."
Hemp and other Fibers
Hemp and other fiber-producing plants as kenaf and sawgrass are currently being investigated as potential building products. Commonly used for numerous purposes before drug laws made its cultivation illegal, non-psychoactive hemp is being rediscovered as a source of fiber, oil, and hurd; these can replace less ecologically sound wood or petrochemical products in a variety of building applications.
Examples include pressed-hemp fiberboards, and use of the inner pith or "hurd" as an additive for a lime-based concrete-like material. Similar studies and experiments are being done with Kenaf and other fibers.
Use of hemp and other fibers have several advantages. Because hemp provides four times the usable fiber per acre as wood, grows in degraded soils, and needs little chemical processing, this annually renewable crop is being considered more and more seriously. Several European countries, including England, Hungary and the Ukraine, have joined major hemp producers such as China to grow this neglected and useful plant for a variety of uses.
Drawbacks include the reliance on expensive imported fiber because of misguided laws which restrict the growing of non-psychoactive strains of the plant in the U.S. Domestic manufacturers are also hampered by the lack of modern processing machinery.