Formwork, Shuttering and Mould Preparation
Forms shape the wall
Formwork must resist the lateral pressure of compaction, stay plumb, and produce the specified thickness and surface. Use stiff panels, adequate walers, clamps, and diagonal bracing. Form faces should be clean and treated with a suitable release agent; porous timber should be wetted or sealed so it does not suck water from the mix. Joints must be tight enough to prevent grout loss but arranged so forms can be stripped without damaging edges. For adobe, moulds should be smooth, tapered slightly for release, and kept clean.
Check forms for plumb, level, alignment, and internal dimensions before placing earth. Bracing only one side is a classic failure; both sides need support, and clamps need sensible spacing. Never use formwork as a working platform or a support for heavy materials.
Traps: flexible forms that bulge under compaction, missing release agent, stripping too early, and forms set out of square. Another trap is assuming thicker formwork is always better while ignoring bracing and clamp spacing.
Worked example: set out a 3 m long, 300 mm thick wall. Check the diagonal measurements: they should be equal. Use a 1.2 m spirit level on both faces and a string line along the top. As a rule of thumb, keep clamp spacing tight enough that the form face deflects no more than about 3 mm under a firm push; if it moves visibly, add walers or reduce lift thickness.