Natural Building - Light straw-clay

History

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.

Architecture

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%.

Suggested Reading:

• 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