The Value of Straw Wattle Walls

I recently received this message from Patti Stouter, who has been a long time advocate and experimenter with earthbags and other natural technologies, especially as a means for surviving earthquakes and other calamities:

I am beginning a test shelter project of straw wattle that may be helpful in both Ukraine and Turkey, so this report of proven performance will be helpful to aid workers.

Earthbag and mesh-enclosed light straw clay have performed well in a Haitian agriculture school now for more than five years. The Haiti Christian Development Project school is in the country outside Gonaives where the climate is hot and somewhat dry, with 28 inches of rain per year. Local builders prize earthbag homes for their cool interiors and potential to resist earthquakes.
One earthbag building near the northern coast needed repairs to its bond beam after a quake several years ago, but its earthbag walls were undamaged. Reinforcing steel in the bond beam may have been placed too close to the wall surface.
Earthbag is a heavy material, requiring labor to build. Heavy walls undergo extreme forces in earthquakes, often concentrating at the wall tops. Lighter walls go up quicker and undergo less force in quakes. Lighter walls can be safer in earthquakes with less exacting detailing.
A special version of LSC (light straw clay) was chosen by HCDP for a dormitory both for it’s light weight and to shorten construction time. Mesh tubing commonly seen in loosely filled erosion control wattles was repurposed for walls. LSC is usually built as infill between wood framing, applied wet into a moveable form that holds it together until it stiffens.When logs made by firmly stuffing straw into stiff mesh tubing are tied or sewed on both sides to unite layers, the mesh acts as a form, adds reinforcement, and makes it difficult for thieves or rodents to dig in. After soaking the straw with clay, earthen plaster levels the surfaces.Wattle walls become stronger with stronger clay, when more clay is worked in and when clay penetrates more deeply into the logs. But to hold up roofs sized for houses or larger buildings, BuildSimple.org recommends a strongly interconnected framework of poles worked through the mesh.Haitian builders hammered rebars into earthbag base walls for their dormitory. Each course of dry straw log was impaled on the rebar.

Clay and straw materials are best finished with a breathable plaster of lime or earth. Because Haiti has no hydraulic lime and shipping (even in better conditions some years ago) was difficult, the builders used cement stucco as a wall finish. Because of the dry climate and good roof maintenance, no repairs have been needed to these inexpensive and lightly insulated walls.