« Permanent Formwork (Stay-in-Place): How It Works, When It Pays — and When Reusable Wins » n'est pas encore disponible en Français

Permanent formwork (also called stay-in-place, sacrificial, or lost formwork) is any forming element left cast into the structure after the concrete cures, rather than being struck and reused. It earns its place on one-off geometry, unreachable voids, or where the form doubles as insulation or a finished face.

Only when the geometry does not repeat. A sacrificial form is paid for in full on every pour, while a reusable film-faced panel rated up to 20 reuse cycles spreads its cost across many pours. The crossover usually lands around the third or fourth repeat, after which reusable is cheaper per pour and gives tighter dimensional control.

Common families include expanded polystyrene (EPS) for foundations and insulation, fibre-cement and GRP boards for columns, light-gauge steel mesh and profiled steel decking for ground beams and composite slabs, PVC or cement wall systems for water-retaining walls, and insulated concrete formwork (ICF) for housing walls.

Yes, as a one-off lost former where stripping is impractical, such as a shaft crown or an awkward soffit pocket, an 18 mm film-faced panel makes a sound sacrificial form. For any geometry that repeats, a reusable phenolic (EN 636-3) or melamine-cored (EN 636-2) panel is the better and cheaper choice.