Natural Building - Light straw-clay
For most of our existence on Earth, we have lived without architects, engineers, designers and manufactured building materials. In many societies, almost everyone knew how to make their own tools and homes. They learned from observation, experiments and practice. In Europe, light straw-clay houses are examples of culture development. This technique, also known as a light clay or a light loam, evolved from a heavier clay method called wattle and daub, which has been used in construction for at least 6.000 years (now mostly in use in the preservation of historic buildings)
Due to the lack of building materials after World War II, interest in clay building was intensified and a standard clay building code was introduced. In Europe during the 1970s and 1980s clay products were tested, improved and used with renewed vigor. As a further result, "straw/clay" was developed.
Due to its simplicity, affordability and creative possibilities, we believe there is rising opportunity and fertile grounds to apply light straw clay technique nowadays.
Post and beam (also called timber frame) is ideal for building light straw clay walls. Structural frame and the weight of the roof are carried by a wood and it is important to be designed in accordance with the International Building Code. Because the timber frame structure is completely surrounded by the clay and fiber enclosure the frame has timeless protection from environmental factors. Timber structures can be deconstructed and then re-used for many following years.
For building our houses we use Greek pine wood. 10x10 cm beams are placed vertically and horizontally on the stone foundation. The space between columns is 15 cm, which makes exterior walls 35 cm thick. The internal walls are 10 cm thick.
Materials for making light straw clay
The tools and experience necessary to build light clay straw walls are minimal.
Straw - Straw can be wheat, rye, oats, rice or barley, and should be free of visible decay and insects. Availability of straw can fluctuate with the season so it is important to have some knowledge of the local agricultural cycles to access the best selection of material. For our constructions we have chosen wheat straw as it was the most locally available type.
Clay soil - Soil should have a minimum clay content of 50% by volume. Making a clay slip is pretty easy: we place soil in the cement mixer (as it’s easier for bigger quantities) and by slowly adding water, it reaches the right consistency, which is that of a heavy cream.
Light straw clay mixture - We place all straw stems in a big table and pour evenly of clay slurry onto the straw. Everything needs to be mixed well by hands until they are thoroughly and evenly coated so as to avoid pockets of dry straw.
Straw bricks - Light straw clay mixture can be replaced by straw bricks. Our straw bricks are made in a special mold, which allows us to adjust the dimensions by movable partitions.The slip-coated straw is placed into the forms and compacted.
Building the walls
Timber battens - should be fitted horizontally to the structure, in order to "lock in" the straw-clay mass. First we nail battens along the one site of a wall. The next step is to fill the wall with light straw clay mixture. Once each layer is complete we nail horizontal batten, to prevent loss of material from the wall, then we tamp next layer of infill until the wall is complete. The material should be pressed good to fill all corners of the wall. Once the wall has dried for a week, we may need to add more mixture in gaps that appear.
Wall drying time depends on the season and climate (wind and relative humidity). Depending on the straw, there are some of missed seeds sprouting, when they shrivel and die, the wall may be dry enough.
The wall can be checked also by moisture meter, the moisture content of the wallsneeds to go below 18%.
- One Straw Revolution: Light Clay Straw Construction. Jacob Schmidt
- Building without borders. Joseph F. Kennedy
- Natural Building Colloquium.An Introduction to Traditional and Modern German Clay Building. Frank Andresen
- Research Report. Initial Material Characterization of Straw Light Clay. JoshuaThornton 2004
A few words about Natural Building
Because of its versatility and widespread availability, earth and straw have been used as construction materials throughout the world since antiquity and particularly soil is one of the oldest building materials; the first freestanding human dwellings may have been built of sod or wattle-and-daub. About 10,000 years ago, the residents of Jericho were using oval, hand formed, sun dried bricks (adobes), which were probably a refinement of earlier cob.
Earthen homes are common in Africa, the Middle East, India, Afganistan, Asia, Europe, South and Cetral America. One-third of the world's population is currently living in homes made of unbaked earth.
A simply definition for natural building, would be any building system which gives value on social and enviromental sustainability. Easy-to-learn techniques based on locally available, raw, renewable and recycled resources, ideally gathered from the site vicinity makes natural building very unique subject which rely heavily on human labor and creativity instead of on capital, high technology, and specialized skills.
Earth construction takes many forms, including adobe, rammed earth, and wattle and daub. By adding a straw, the number of functional methods of natural constructions is expanded to Straw bale, Light straw-clay, Straw bricks and Cob. This provides a wide range of possibilities to choose one's own method for natural construction according to the climate zone and the availability of raw materials.
All the techniques of Natural Building are very flexible and forgiving medium. It needs dedication more than physical strength and willingness to experiment, more than skills. Building with natural materials is an easy way to go on a big adventure!
Climate and Materials
The right method for natural building varies according to the climate of each place. Temperature and availability of materials for construction are playing the main role. For the desert areas the ideal technique is cob which holds the night's cool throughout the day, slowly heating up to release the day's warmth at night. For cold climate the insulation is needed and here with a help is coming a straw which is an amazing isolator for walls, straw bale technique is a solution for this kind of climate.
Availability of materials is important for choosing the type of foundations. Stone is the best and will still be the best a few thousand years from now, after the home has returned to the elements. Collected stones are placed on the ground like puzzle. To eliminate chemicals elements even within the foundations, cob or earthen mortar is used to avoid the moving of stones.
In dry climates a good option for foundation is the use of agricultural bags filled with earth tamped. This concept was originally presented as a Superadobe technology by architect Nader Khalili to NASA for building habitats on the moon and Mars!
- The Cob Builders Handbook. Becky Bee
- Natural Building Colloquium (The Case for Natural Building). Michael Smith