Tamp each earthbag with a flat-plate hand tamper until its top is flat, it stands about 10-12 cm high, and it has spread to fill the full wall thickness. The way the bag responds under the tamper tells you whether the fill is right: a springy bag is too wet, a crumbling bag too dry, and a bag that will not flatten is overfilled.
Part of Earthbag Building
Tamping compacts the fill inside each bag so that it sets hard and the course carries load evenly.
The Bag Tells You What Is Wrong With The Fill
Tamping does the work of compaction. Done properly it flattens the bag to a uniform thickness, spreads it across the wall width and packs the fill so it sets hard. Done badly it leaves soft spots that settle later. Because you feel the response under the tamper on every bag, tamping is also your continuous quality test.
What You Need
- A hand tamper: a flat plate on a handle, such as plywood nailed to a broom handle.
- Fill that already passes the ball test; see Fill Ratios and Consistency.
- A string line and level to check the finished course.
Method: Tamp, Read, Check
Step 1: Set the bag in place, fold side down, filled to about 80%.
Step 2: Tamp vigorously over the whole top, working from the middle toward the edges and including the corners and ends. A bag tamped only in the centre domes upward.
Step 3: Read the response. The bag should feel firmer with each pass until it stops compressing. Stop when the top is flat and the bag is roughly 10-12 cm high.
Step 4: Check the course against the string line. Shim or tamp individual bags to bring them level.
Step 5: Lay the wire and place the next course.
When Tamping Goes Wrong
| What you feel or see | What it means | What to do |
|---|---|---|
| Springy, water squeezes out | Fill too wet | Dry the pile, re-mix |
| Grains crumble, bag will not hold together | Fill too dry or too sandy | Wet or add clay |
| Bag will not flatten | Overfilled | Remove some fill |
| Soft pocket in a flat bag | Uneven fill | Re-open, mix, refill |
| Course height varies along the wall | Uneven filling | Fill by a consistent measure |
Common Mistakes
- Tamping only the centre. Edges stay loose and the wall rocks.
- Tamping on top of barbs. Lay the wire after the course is tamped and level, not before.
- Skipping the level check. Errors compound across courses.
Safety
Repetitive strain and rebounding tools
Hours of tamping strain wrists, shoulders and the back, so rotate tasks every few bags. Keep fingers clear of the tamper plate and stand clear of a crew member swinging a tamper near a corner.
What’s Next
- Learn next: Barbed Wire Between Courses — locking the tamped course
- Combine with: Bag Filling and Placement — the step before tamping