Fibre Reinforced Facade Encyclopedia: Manufacturing
Formwork is the mould that holds fresh concrete or a wet laminate in the required shape until the material has gained enough strength to support itself. It is called shuttering in the United Kingdom and parts of Asia, and the temporary structure that supports horizontal formwork is called falsework or shoring. Formwork does three jobs at once: it sets the geometry, it carries the pressure of the wet material, and it gives the finished surface its texture, because a concrete face is a negative of the mould face and nothing else.
Formwork and falsework typically account for 35 to 60 per cent of the cost of an in-situ concrete frame, far more than the cement, aggregate and steel combined. On a moulded facade panel the mould can exceed the cost of the concrete by an order of magnitude.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Cost share of an in-situ frame | 35 to 60% of frame cost | More than cement, aggregate and steel combined |
| Design load, vertical | Self weight plus wet concrete at 24 kN/m³ plus a construction live load of 1.5 kN/m² or more | AS 3610 and AS 3610.1 govern in Australia |
| Design load, horizontal | Concrete pressure to a full fluid head of about 24 kPa per metre of pour | Reduced by set rate, temperature and pour rate |
| Typical striking time, walls and columns | 12 to 24 hours | Vertical faces carry no load once set |
| Typical striking time, soffits | 7 to 21 days, or to a specified strength | Backpropping usually required |
| Surface finish classes | Class 1 to Class 5 under AS 3610 | Class 1 is the tightest, used for exposed architectural faces |
| Panel system reuse | 50 to 500 uses for steel and aluminium faces | Plywood faces 5 to 30 uses depending on finish class |
| Facade mould reuse | 1 to 200 casts | Material dependent; see cnc-formwork |
| Deflection limit, architectural faces | Commonly span over 360 or 3 mm, whichever is less | Tighter for Class 1 off-form work |
What formwork has to do
Fresh concrete behaves as a liquid until it sets, so a vertical form is loaded like a tank rather than like a wall. Horizontal pressure rises with the depth of unset concrete, approaching a full fluid head of roughly 24 kPa per metre of pour. Fast pours, cold weather, retarders and self-compacting mixes keep the concrete fluid for longer and push the pressure toward that full hydrostatic value; slow pours in warm conditions let the lower layers stiffen and cut it. Blowouts on site are almost always a pressure calculation problem rather than a materials problem.
Horizontal formwork carries different loads: wet concrete at about 24 kN per cubic metre, the form itself, a construction live load for workers, plant and stacked material, and impact from placing. Soffit forms are stiffness-governed, because a deck that deflects during the pour locks that deflection into the slab permanently.
The third job, surface finish, most often decides the system. Concrete reproduces the mould face exactly, including joints, nail heads, grain, release agent streaks and leakage. AS 3610 sets finish classes from Class 1 for prominent architectural off-form faces to Class 5 for concealed work, and the class dictates the face material, joint layout, permitted reuses and release agent.
Types of formwork
- Traditional timber formwork: sawn bearers and studs with a plywood or formply face, cut on site. Labour intensive, but unbeatable for one-off shapes, odd junctions and small pours.
- Engineered panel systems: modular steel or aluminium frames with a plywood or plastic face, hired by the square metre. Fast and dimensionally repeatable where the same wall or column repeats.
- Table and flying forms: large preassembled soffit tables craned floor to floor on repetitive towers.
- Slipform: a short form, usually 1.2 metres deep, jacked continuously upward while concrete is placed at the top and emerges set at the bottom. Cores, silos and chimneys.
- Climbing and jumpform: a form lifted in stages up the structure it has just cast, crane-lifted or self-climbing on hydraulic rails. Cores and tall piers.
- Permanent or stay-in-place formwork: left in the works as part of the finished element, such as profiled steel decking, insulated concrete forms, fibre cement plank and thin GRC shells on bridge parapets and tunnel portals. See stay-in-place-formwork and lost-formwork.
- Fabric formwork: tensioned geotextile producing curved, variable-section members with very little material. Still largely specialist work.
Face materials and release
The face material determines both the finish and the number of reuses. Film-faced plywood, or formply, is the default, good for 5 to 30 pours depending on the finish class. Steel faces give a very smooth finish and last for hundreds of uses; plastic and glass fibre faces suit repetitive moulded shapes; rubber and polyurethane liners cast texture and relief; timber boards are used where board-marked concrete is the intended aesthetic.
Release agents let the form strike without tearing the surface. Chemically reactive agents are preferred for architectural work, because neat oils stain and emulsions cause dusting and colour variation. Applied too heavily, release agent is a common cause of blotchy colour on an off-form face, a defect the concrete supplier cannot fix. See off-form-finish and colour-consistency.
Moulds for moulded facade panels
Everything above describes formwork for in-situ and precast structural concrete. Facade work in glass fibre reinforced concrete (GRC, GFRC), fibre reinforced polymer and glass fibre reinforced gypsum uses the same principle with different economics. The material is thin, so the mould carries almost no pressure. What it has to do instead is hold a complex three dimensional surface to tight tolerance, survive repeated demoulding without distortion, and give a face good enough to become the visible face of the building.
For sprayed GRC the mould is an open single-sided tool. Slurry and chopped alkali resistant glass are sprayed into it in layers and roller compacted, so the mould face is the external face of the panel and any defect in it appears on the building. For hand lay-up and vacuum infusion in FRP the mould is usually a female tool finished to a high gloss, because the gel coat takes its surface directly. Mould materials are timber and MDF for prismatic shapes, tooling board and glass fibre for high-reuse production tools, and machined polystyrene for double-curved and freeform geometry. CNC machining changed the economics of that last category, because a mould that once had to be lofted and hand-faired is now milled directly from the Rhino or Revit model. See mould-making, sprayed-grc, cnc-formwork and double-curvature.
The distinction is worth stating plainly. On a structural concrete job formwork is a cost minimised by repetition. On a moulded facade the mould is the principal tooling cost, and the number of panels taken off one mould is usually the largest single variable in the price.
Standards and references
- AS 3610 Formwork for concrete, and AS 3610.1 Documentation and surface finish
- AS/NZS 1170 series (structural design actions) for formwork and falsework load cases
- AS 5100.2 Bridge design, for falsework in bridgeworks
- Safe Work Australia Model Code of Practice: Formwork and Falsework
- BS 5975 Code of practice for temporary works procedures and the permissible stress design of falsework (UK)
- ACI 347 Guide to Formwork for Concrete and ACI SP-4 Formwork for Concrete (US)
- CIRIA Report 108 Concrete pressure on formwork
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products (moulds for GRC)
Related terms
Questions specifiers ask
What is the difference between formwork and shuttering?
They are the same thing. Shuttering is the usual term in the United Kingdom, India and parts of Asia; formwork is the term used in Australia, the US and in AS 3610. Falsework is different again: it is the propping and shoring that holds the formwork up.
How long before formwork can be stripped?
Columns and walls are commonly stripped at 12 to 24 hours because they carry no load once the concrete has set. Soffits are held until the slab reaches a specified strength, typically 7 to 21 days, and usually need backpropping afterwards. The striking regime is part of the formwork design, not a site decision.
How much pressure does wet concrete exert on formwork?
Up to a full fluid head of about 24 kPa per metre of unset concrete. The actual pressure is lower when the pour is slow, the weather is warm and the mix stiffens quickly, and close to full hydrostatic for fast pours, cold conditions and self-compacting concrete.
What is permanent formwork?
Formwork that is not stripped and stays in the finished works, such as profiled steel decking, insulated concrete forms, fibre cement sheet and thin GRC shells used on bridge parapets and tunnel portals. It is also called stay-in-place or lost formwork.
What formwork is used for curved facade panels?
Single-sided moulds machined by CNC router from polystyrene, tooling board, MDF or timber, then coated and sealed. The mould is milled directly from the 3D model, which makes double-curved and freeform panels practical. See cnc-formwork.
Working out whether your facade geometry is mould-friendly? We build CNC-machined moulds for GRC, FRP and GRG panels and can advise on rationalisation before the tooling is committed. Talk to our engineering team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.