Water attacks an earthbag wall by four routes: rising from the ground, splashing up from the ground, running down the face from the roof, and standing against the base in a flood. Each is answered by a different defence, namely gravel-filled base courses, a drained foundation, plaster and roof protection, and time to dry out after brief flooding.
Part of Earthbag Building
Moisture management for an earthbag wall means finding which path water is using and closing it, because the fill is earth and softens when wet.
Match The Defence To The Route Water Takes
Water arrives by four routes, set out below. Earthbag walls tolerate more water than most natural building methods: the parent article notes that walls below the water line survive brief flooding if allowed to dry afterward. But a wall that stays wet is a different matter. The fill is clay-bearing earth, and long wetting weakens the bags, loosens plaster and invites decay.
| Route | Defence |
|---|---|
| Rising ground water | Gravel-only base courses, rubble trench with drain |
| Splash-back from the ground | Raise the stem, shape the ground away from the wall, plaster |
| Rain on the wall face | Plaster, roof overhang |
| Standing water in a flood | Allow the wall to dry fully before loading or plastering |
Rising water is the one that gravel courses address. In fine soil water rises by capillary action, and the finer the pores the higher it climbs; in gravel the voids are too wide to lift it. That is why the first two or three courses are filled with gravel only.
What You Need
- A drained foundation with an outlet; see Rubble Trench and Grade Beam.
- Gravel base courses; see Gravel-Filled Stem Courses.
- Plaster on all exposed faces; see Plaster Systems.
- A roof with a generous overhang over the walls, so rain does not run down the face.
Method: Diagnose Before You Repair
Step 1: Look for a damp line at the base. A band of dampness or staining near the bottom of a wall points to rising or splashing water.
Step 2: Look at the plaster. Bulging, flaking or soft plaster in patches points to water getting in behind it, often from the roof line or around openings.
Step 3: Look at the ground and the outlet. Water standing against the wall base, or a drain outlet that is blocked or buried, tells you the drainage has failed.
Step 4: Fix the source first. Clear the outlet, regrade the ground, repair the gutter or overhang, then repair the wall. A repair applied to a wall that is still wet fails.
Step 5: After a flood, let the wall dry. Do not plaster or load a wall until it has dried out.
Common Mistakes
- Plastering over a wet wall. The plaster seals moisture in and then fails.
- Treating the wall instead of the source. Patching the plaster while rain still runs down the face wastes the work.
- Burying the drain outlet. Backfilled or silted outlets turn a drain into a water tank.
Safety
A saturated wall may be weakened
Wet earth fill is softer and heavier. Do not remove sections of a wall that has been in flood water, and brace it before you open it up. Dig any drain outlet trenches with sloped or shored sides.
What’s Next
- Learn next: Waterproofing Methods — sealing the wall
- Combine with: UV Protection for Bags — the other thing that destroys unplastered bags