Earthbag walls can be built from individual woven polypropylene grain bags of about 50 kg capacity, from continuous polypropylene tubing laid as a coil, or from burlap bags as a biodegradable alternative. Polypropylene is the most durable but degrades in sunlight within weeks to months, so any bag type must be covered with plaster before the bag fabric fails.
Part of Earthbag Building
The bag is the mould that holds the fill while it is tamped into a course; once the earth has set and the wall is plastered, the bag’s job is largely done.
The Bag Is A Mould, So Choose It For The Building Phase
The bag holds loose fill in place while you tamp it flat, and it keeps the course in shape until the earth sets and the plaster takes over. That explains the Earthbag Building overview’s observation that burlap can rot away once the earth has set and plaster is on, while polypropylene must be protected from sunlight until then. The choice between types is therefore about supply, speed, and how long the bag will be exposed.
What You Need
- Grain bags (50 kg size). Woven polypropylene, about 45 x 75 cm when empty. These are the most common and the easiest to source, because they are used in agricultural and industrial areas everywhere.
- Continuous tubing (superadobe). Tubular polypropylene mesh laid in a continuous coil rather than as separate bags. It is faster, because there is no tying or folding of individual bags, but harder to source after a collapse.
- Burlap or hessian bags. A natural-fibre alternative. They are biodegradable, which is acceptable because the bags are only needed during construction.
Method: Pick And Check The Bag
Step 1: Match the bag to the supply you have. If you can find a few hundred identical grain bags, use bags. If a roll of tubing is available, use it for long straight runs, where it saves the most time.
Step 2: Inspect every bag for sun damage. Old polypropylene that has sat in sunlight becomes brittle. Crumple a corner and tug it: if the weave tears easily, reject it, because the fabric has to survive filling and tamping.
Step 3: Shake out and check for residue. Feed, fertiliser and chemical bags can hold dust or residue. Empty them outdoors.
Step 4: Decide the plaster deadline. With polypropylene, plan plaster immediately after the wall is complete. With burlap, the bag will eventually rot, so the plaster and the set fill must carry the wall; see the caution below.
Choosing A Bag Type
| Type | Strength | Weakness |
|---|---|---|
| Polypropylene grain bags | Common, durable once plastered | Degrades in sunlight within weeks to months |
| Continuous tubing | Fast, no tying | Harder to source after a collapse |
| Burlap or hessian | Biodegradable once the wall is plastered | Rots, so the set fill must hold the wall |
Common Mistakes
- Using sun-damaged bags. They may split during tamping and give weak courses.
- Using burlap with loose, uncohesive fill. The overview’s note that burlap can rot away depends on the earth having set and being plastered. A sandy fill with little clay does not set, so rotting burlap would leave the wall without confinement. Reserve burlap for clay-bound fill and plaster promptly.
- Leaving polypropylene unplastered. Unplastered walls left in the sun fail within one to two years.
Safety
Polypropylene is a flammable plastic
Woven polypropylene bags burn and melt. Keep fires, hot work and cooking away from an unplastered earthbag wall until the plaster is on.
What’s Next
- Learn next: Fill Materials and Testing — what goes inside the bag
- Combine with: UV Protection for Bags — keeping bags alive until plaster