Formwork is the temporary mold system that gives wet concrete its final shape while it gains strength. It is used to build walls, beams, slabs, columns, foundations, and many other concrete structures. Because fresh concrete is heavy and fluid, formwork must resist pressure, hold exact dimensions, and keep workers safe.
Good formwork improves surface quality, reduces waste, and helps a construction project stay on schedule.
A formwork system usually includes sheathing panels, studs, walers, ties, braces, and supports that work together like a temporary structure. Wet concrete pushes sideways on vertical forms and downward on horizontal forms, so engineers estimate loads before choosing materials and spacing. As cement hydrates, the concrete hardens and can gradually carry its own weight.
Once the concrete reaches enough strength, the formwork is stripped, cleaned, and often reused.
Key Facts
- Fresh concrete density is about 2400 kg/m^3, so its weight load is W = mg.
- Pressure from wet concrete increases with depth and can be estimated by P = ρgh for fluid-like concrete.
- Formwork must resist dead load, live load, impact load, and lateral pressure from fresh concrete.
- Common formwork materials include timber, plywood, steel, aluminum, and plastic composites.
- Curing strength depends on hydration, temperature, water content, cement type, and time.
- Safe stripping time is based on required concrete strength, not just the number of hours after pouring.
Vocabulary
- Formwork
- A temporary mold and support system used to shape and hold fresh concrete until it hardens.
- Sheathing
- The flat panel surface that directly touches the wet concrete and gives it its finished shape.
- Waler
- A horizontal reinforcing member that spreads concrete pressure across the form panels.
- Tie
- A connector that holds opposite form faces together so they do not spread apart under concrete pressure.
- Curing
- The process in which concrete gains strength as cement reacts with water over time.
Common Mistakes to Avoid
- Treating formwork as only a container is wrong because it also acts as a temporary load-bearing structure that must be designed for forces.
- Removing formwork too early is wrong because concrete may look solid before it has enough strength to support itself safely.
- Ignoring lateral pressure on wall forms is wrong because wet concrete can push outward strongly, especially near the bottom of the pour.
- Spacing braces or ties by guesswork is wrong because uneven support can cause bulging, leaks, misalignment, or collapse.
Practice Questions
- 1 A formwork panel supports 0.80 m^3 of fresh concrete. If the density of concrete is 2400 kg/m^3, what is the mass of the concrete and its weight in newtons using g = 9.8 m/s^2?
- 2 A vertical wall form is filled with fresh concrete to a height of 2.5 m. Estimate the pressure at the bottom using P = ρgh with ρ = 2400 kg/m^3 and g = 9.8 m/s^2.
- 3 Explain why a tall column form needs ties and braces even if the form panels are made of strong plywood.