sideform
A process for setting concrete which uses forms to confine the concrete to the desired width.
sideform: formwork that controls concrete width
A sideform is a temporary or permanent vertical board or panel positioned alongside freshly placed concrete to constrain it to a specified width and maintain a clean edge during curing. In strip foundations, floor slabs, and sidewalk pours, the sideform prevents the wet concrete from spreading laterally beyond the design footprint while providing a smooth finished face.
Sideforms are typically made from timber (often softwood boards 25 to 50 mm thick), plywood, or aluminum extrusions, depending on the concrete finish required and the frequency of reuse. They are held in place by stakes, clamps, or bracing driven into the subgrade or attached to a base course. The interior surface of the sideform must be clean and sealed or oiled to prevent concrete bond and allow easy removal after the concrete has set to the required strength, usually 24 to 72 hours depending on ambient temperature and mix design.
In mass concrete work, sideforms also serve a secondary function: they contain concrete that may be manually vibrated or mechanically consolidated, ensuring uniform density. When concrete is placed against an unconfined edge, segregation and honeycombing can occur along that face. The pressure exerted by wet concrete, hydrostatic load, increases with depth and concrete temperature, so sideforms must be properly braced to resist buckling or displacement.
Variants and durability
Permanent sideforms, such as concrete curb forms or cavity wall formwork, may remain in place as part of the finished structure. Reusable metal sideforms reduce waste and labor cost on repetitive work like industrial floors or bridge decks, but require careful cleaning and maintenance between pours. Timber sideforms are the most economical for one-off or small projects but deteriorate rapidly if left in damp conditions.
Common defects arise from inadequate bracing (form bulge or misalignment), concrete leakage through joints, or form removal before concrete has cured sufficiently. The contact face between sideform and concrete, the formed surface, must be inspected before striking; spalling, blowholes, and surface voids indicate insufficient consolidation or poor form condition. Sideforms are distinct from edge formwork in that they specifically control lateral width rather than depth.