Polypropylene earthbags degrade rapidly in sunlight, in weeks to months, and an unplastered wall left in the sun fails within 1-2 years, so sunlight on the bags must be limited from the day they are filled. Cover stockpiled bags and the unfinished wall, and plan the plaster to go on immediately after the wall is complete.
Part of Earthbag Building
Ultraviolet light breaks down woven polypropylene, so the bags have a limited working life unless shaded or plastered.
Sunlight Is A Deadline, Not A Gradual Nuisance
The parent article gives two timescales: bags degrade in weeks to months, and an unplastered wall fails within 1-2 years. The first is the practical building deadline and the second the outer limit. The wall’s strength depends on the bags holding the fill in shape until the plaster takes over, so a bag that has turned brittle in the sun is a bag that will tear when the wall settles.
What You Need
- Covers for stockpiled bags: tarps, sheeting or shaded storage.
- Temporary covers for the unfinished wall.
- Plaster ready to go before the wall is finished; see Plaster Systems.
Method: Shorten The Exposure
Step 1: Store unused bags in shade, under cover, until the day they are used.
Step 2: Fill and place bags as close together in time as possible, so no part of the wall waits long.
Step 3: Cover the work at the end of each day and cover the finished wall until plaster begins.
Step 4: Have the plaster materials prepared before the last course goes on.
Step 5: Inspect exposed bags by crumpling a corner: brittle, easily torn fabric means that stretch needs plaster urgently or replacement.
Common Mistakes
- Leaving the wall to “settle” for months before plastering. It uses up the bags’ life.
- Storing bags in the sun before use.
- Covers that trap water. Wet bags sitting under plastic soften the wall; allow airflow.
Safety
Polypropylene burns
Sun-weakened bags are no less flammable. Keep fires, torches and cooking away from unplastered walls and stockpiled bags.
What’s Next
- Learn next: Waterproofing Methods — the other protection job
- Combine with: Bag Types and Alternatives — burlap’s different lifespan