An earthbag wall needs four materials: woven polypropylene bags or tubing, fill soil of roughly 70% sand and gravel to 30% clay, two strands of barbed wire for every course, and a plaster to cover the finished bags. The bags and wire are usually salvaged from farms and fence lines, while the soil is dug on site, so locate the bags and wire first because they are the scarce items.
Part of Earthbag Building
Earthbag walls are courses of earth-filled bags tied together with barbed wire and covered in plaster. The materials are cheap and mostly local, but each has a specification that decides whether the wall stands.
The Wall Is Only As Good As Its Four Ingredients
An earthbag wall is a stack of filled bags, each course locked to the one below by barbed wire, then sealed in plaster. Take away any one of the four ingredients and the wall fails in a predictable way: no bags and there is nothing to hold the fill in shape, poor fill and the courses do not set hard, no wire and the wall slides apart under wind or earthquake loads, no plaster and sunlight destroys the bags.
Because earth is the bulk of the wall, the sourcing question is really about the three small items: the bag, the wire and the plaster binder. The soil is almost always found on the building site or within a short haul.
What You Need
- Bags or tubing. Woven polypropylene grain bags, sandbags or feed bags are the standard, and the common 50 kg grain bag is about 45 x 75 cm when empty. Continuous tubing is faster to lay but harder to find after a collapse. See Bag Types and Alternatives.
- Fill soil. About 70% sand and gravel to 30% clay, a sandy clay or clayey sand. Test it before you commit: Fill Materials and Testing.
- Barbed wire. Two strands of 4-point wire per course, salvaged from fence lines, farms and agricultural supply stores. Alternatives exist but are weaker substitutes: Barbed Wire and Alternatives.
- Gravel for the first two or three courses, which must be gravel only with no clay.
- Plaster materials. Clay and sand for interior earth plaster, lime for the exterior. See Plaster Systems.
- Basic tools. Listed in Tools Required.
Method: Source In The Order That Can Stop The Project
Step 1: Count the bags you can actually get. Estimate how many courses the building needs and multiply by the bags per course before you dig a single spadeful. Bag supply, not soil, is what usually caps the size of the first building.
Step 2: Locate the wire. Walk fence lines and farm yards for abandoned barbed wire. You need it in quantity: two strands run along every course of every wall.
Step 3: Test the soil. Take samples from the building site and from any nearby cut or bank. Run the jar, ball and ribbon tests described in the fill article. If the site soil is outside the range, you will need a second source to blend with it.
Step 4: Sort out the plaster binder early. Lime takes time to prepare, and the bags must be plastered before sunlight degrades them. A wall finished without plaster ready is a wall on a countdown.
Common Mistakes
- Starting the wall before the plaster is possible. Polypropylene bags degrade rapidly in sunlight, and unplastered walls left in the sun fail within one to two years.
- Treating any soil as fill. Pure sand or pure clay both give a poor bag; the 70/30 mix is the target for a reason.
- Salvaging wire last. It is the item that gives the wall its tensile strength.
Safety
Salvaged barbed wire and contaminated bags
Barbed wire punctures skin and recoils when cut under tension, so wear heavy gloves and eye protection and keep an up-to-date tetanus vaccination if you can. Used feed and fertiliser bags may carry chemical residue: shake them out outdoors and keep your face away from the dust.
What’s Next
- Learn next: Foundation and First Courses — what the wall sits on
- Combine with: Permanent Settlement Site Selection — choosing ground with good soil and drainage