Plaster finishes an earthbag wall and protects it in three ways: it blocks sunlight that degrades the bags, keeps rain out of the earth fill, and binds the bags into a single monolithic wall. It must go on before the bags deteriorate, because unplastered polypropylene walls left in the sun fail within 1-2 years.
Part of Earthbag Building
Finishing an earthbag wall means plastering it, shielding the bags from sunlight until then, and sealing the wall against water.
Plaster Is Part Of The Structure, Not Decoration
The plaster does three jobs: UV protection, weather resistance and structural integration. The rough texture of earthbag courses grips plaster well, and the hollows between courses act as keys. The three topics below cover the detail:
- What plaster to use: Plaster Systems.
- Protecting bags before plaster: UV Protection for Bags.
- Keeping water out: Waterproofing Methods.
What You Need
- A completed wall with the bond beam and roof (or temporary covers) in place.
- Plaster materials: clay and sand for interior earth plaster, lime for exterior; see Lime and Cement.
- Mixing and application tools.
Method: The Order Of Finishing
Step 1: Cover exposed bags during construction.
Step 2: Finish the wall and roof so rain cannot run onto fresh plaster.
Step 3: Apply the plaster directly to the bags; no mesh is usually necessary.
Step 4: Cure it properly, slowly and damp for lime plaster.
Step 5: Inspect the wall after the first wet season.
Common Mistakes
- Delaying plaster. UV degrades bags within weeks.
- Plastering before the roof. Rain washes fresh plaster.
- Leaving wire or bag fabric exposed.
Safety
Lime burns skin and eyes
Lime is strongly alkaline: wet lime has a pH of about 12-13, as Plaster and Lime Wash notes for limewash. Splashes cause alkali burns, and in the eye can cause permanent damage. Wear goggles and gloves, and if lime reaches skin or eyes flush with clean water for at least 30 minutes, the figure given for alkalis in Chemical Burns, then seek care.
What’s Next
- Learn next: Plaster Systems — which plaster for which face
- Combine with: Plaster and Lime Wash — a finishing coat