Formwork / Shuttering

Formwork is the temporary mould or structure that supports concrete during placement and hardening, until the concrete is structurally adequate to support itself. Indian Standards: IS 14687:1999 (formwork specification), IS 4014:1967 (steel formwork), IS 11827:1989 (timber formwork), IS 16172 (mechanical splices). Formwork is a major construction cost element — typically 15-25% of total RCC project cost. Reusability and turnaround time directly impact project economics.

Formwork materials: (1) Timber — traditional, flexible, suitable for irregular shapes; reusable 5-10 times. (2) Plywood — common for slabs and walls; 6-mm Marine grade BWP; reusable 8-15 times. (3) Steel — reusable 50-100 times; high initial cost; common for repetitive elements (columns, walls, flat slabs). (4) Aluminium — lightweight, faster to handle; 50-200 cycles; popular for high-rise construction (Mivan system from Pune developer Eazi Mivan). (5) Plastic — emerging system; 100+ cycles; specialty applications. The selection depends on project size, repetition, schedule, and budget.

Design considerations: (a) Loads — fresh concrete pressure, equipment, workers, plus impact during pour; (b) Stiffness — formwork must not deflect more than 1/270 of span under load; (c) Stripping time — IS 456 Cl. 11 specifies minimum strip times: 16-24 hours for column sides (vertical only); 7 days for beam soffits; 14 days for slab soffits; longer for cantilevers. (d) Surface finish — formwork surface determines concrete surface; smooth shutter → smooth concrete; rough shutter → rough concrete. (e) Reuse — proper cleaning and oiling between uses extends life. Common Indian formwork issues: (a) inadequate bracing causing deflection during pour; (b) early stripping causing concrete cracking or crushing; (c) leaking joints causing slurry loss and honeycombing; (d) inadequate alignment causing dimensional defects. Pre-pour formwork inspection (verticality, alignment, bracing, surface condition) is mandatory.