04/12/2025
The sequence of building column formwork (shuttering) and the concrete pouring process are critical steps in construction that ensure the column is structurally sound and has the correct shape.
I. ERECTING THE COLUMN FORMWORK (SHUTTERING)
The formwork assembly follows a specific sequence to ensure stability, watertightness, and alignment before pouring the concrete.
1. PREPARATION AND SETTING OUT
âĸ Locate the Column: The exact position of the column is marked on the foundation or slab using a center line and corner lines.
âĸ Fix Starter Bars: The reinforcing steel (rebar cage) for the column must already be positioned and tied securely, extending from the footing or lower slab.
âĸ Apply Release Agent: The inner face of the plywood panels (the surface that touches the concrete) is coated with a non-stick release agent (like form oil) to prevent the concrete from adhering, which makes stripping the formwork easier and cleaner.
2. ASSEMBLY
âĸ Erect the First Panel: One face of the plywood formwork is lifted into position and temporarily supported.
âĸ Erect Remaining Panels: The other three panels are placed, forming a box around the rebar cage.
âĸ Fix Wooden Patties: The wooden patties (horizontal battens) are fixed externally to the plywood faces, providing immediate support. The spacing is determined by the expected concrete pressure (closer spacing near the bottom).
âĸ Place and Tighten Clamps (Shikanja): The adjustable steel clamps (shikanja or yokes) are placed around the wooden patties at the specified vertical intervals and tightened securely. Wedges (chavi) may be driven into the clamps to achieve maximum tightness and rigidity.
âĸ Plumb and Brace: The formwork is checked for plumb (perfect verticality) using a plumb bob or spirit level and adjusted. External bracing (diagonal supports tied to the ground or surrounding structure) is added to ensure the formwork cannot shift or tilt during the pouring process.
đˇ. CONCRETE POURING AND CURING
The process of filling the formwork requires careful attention to avoid defects in the final column.
1. POURING
âĸ Inspection: A final check is made to ensure the formwork is clean, tight, plumb, and properly braced.
âĸ Controlled Pouring: Concrete should be poured in layers or lifts, ideally not dropping the mix from a height greater than about 1.5 meters to prevent segregation (where the aggregates separate from the cement paste).
âĸ Compaction: As the concrete is poured, it must be properly compacted using a mechanical vi****or. The vi****or ensures the concrete settles fully, eliminates air pockets (honeycombing), and achieves maximum density, increasing the final strength. The vi****or should be lowered slowly and evenly into each layer.
2. CURING AND STRIPPING
âĸ Curing: Once the column is poured, it is left undisturbed. Curing is the process of maintaining satisfactory moisture and temperature conditions for a period of time after placement. This prevents the concrete from drying out too quickly, allowing the cement hydration process to complete and achieve the desired strength.
âĸ Stripping: The formwork is stripped (removed) only after the concrete has gained sufficient strength to support its own weight and any loads that might be applied. Standard construction codes specify minimum stripping times (often 24 to 48 hours for vertical members like columns, but this depends on the concrete mix design and ambient temperature). The process involves carefully loosening and removing the clamps, braces, patties, and finally the plywood panels without damaging the green concrete.
The video below demonstrates how column formwork is set up.
