Formwork and scaffolding

Formwork is the temporary mould that shapes fresh concrete until it can support itself; falsework is the temporary structure, props and frames, that holds it up. Together they can be a third or more of the cost of a concrete frame, and their failure is one of the commonest causes of fatal construction accidents, so they are engineered, not improvised.

Formwork must be strong enough for the weight of wet concrete, reinforcement and workers, stiff enough to keep the finished surfaces within tolerance, tight enough not to leak grout, and easy to strip and reuse. Materials include plywood with timber or aluminium bearers, steel panels, aluminium systems for repetitive housing, and special climbing and slip forms for tall cores and towers.

Fresh concrete pushes outward on wall and column forms like a liquid. If a pour is placed quickly, the full hydrostatic pressure, density times height, can develop; slower pours and setting concrete reduce it. Ties through the wall carry this pressure from one face to the other, and their spacing is set from the tie capacity. Props under slabs are checked as columns for buckling, and the whole falsework must be braced against sideways loads.

Stripping times depend on the element, the concrete and the weather; soffit props remain until the concrete is strong enough, often with re-propping of lower floors. Scaffolding gives safe working platforms with guardrails, toe boards and proper ties to the building. IS 14687 guides falsework for concrete and IS 4014 covers steel tubular scaffolding.