Shuttering (Formwork) Guide
Shuttering — more formally called formwork — is the temporary mould that holds wet concrete in shape until it gains enough strength to support itself. Get it wrong and it affects every part of the finished concrete, no matter how good the mix design is.
What shuttering has to do
Formwork isn't just a container. While concrete is wet, it behaves almost like a fluid and exerts real lateral pressure on the formwork — increasing with pour height and rate, and affected by temperature and mix consistency. The formwork has to resist that pressure without bulging, bowing or leaking, hold the correct final shape and dimensions, and come apart cleanly afterward without damaging the concrete.
Common formwork materials
- Timber — traditional, flexible for irregular shapes, relatively low cost, but can absorb moisture, warp, and typically has a shorter reuse life than other options.
- Plywood (often faced/coated) — widely used for a smoother finish than raw timber, moderate reuse life, commonly used as the face material even when timber forms the supporting frame.
- Steel — high reuse count, gives a very smooth finish, dimensionally stable, but heavier and more expensive upfront — economical mainly where the same formwork is reused many times.
- Plastic / composite panels — lightweight, good reuse life, resistant to moisture absorption, increasingly used for repetitive standard shapes.
- Aluminum formwork systems — lightweight yet strong, very high reuse counts, common on large repetitive residential/commercial projects where speed matters.
Key requirements, in practice
- Strength and stiffness — formwork and its supporting props/ties must resist the actual lateral pressure of wet concrete for the planned pour rate and height, without excessive deflection.
- Leak-tight joints — gaps let cement mortar/grout escape, which can leave honeycombing behind (see our honeycombing guide) and a poor surface finish.
- Correct alignment and dimensional accuracy — checked and braced before pouring, since it's very difficult to correct a misaligned pour after the concrete has set.
- Appropriate release agent — applied to the form face so it releases cleanly (stripping) without damaging the concrete surface or, for architectural finishes, without staining it.
- Correct striking (stripping) time — formwork must stay in place until the concrete has gained enough strength to support itself and any construction loads; stripping too early risks damage, sagging, or worse for load-bearing elements. This time depends on the element, the concrete's actual strength gain, and ambient conditions — specified minimum periods should always be checked against the applicable code and project specification rather than assumed.
Frequently asked questions
Is shuttering the same thing as formwork?
Yes — "shuttering" is a widely used term (especially in South Asian and some Commonwealth construction practice) for what's more formally called formwork in most codes and international literature. They mean the same thing.
Why does pour rate affect the formwork design?
Wet concrete pressure on formwork builds up during placing and only starts reducing once the concrete begins to stiffen. A faster pour rate (more concrete placed before earlier layers start to stiffen) generally increases the maximum lateral pressure the formwork must resist, so pour rate is a real input to formwork design, not just the final pour height.