Fibre Reinforced Facade Encyclopedia: Manufacturing
Demoulding is the operation of releasing a cast panel from the mould it was formed in. It happens once per panel per mould, and it is the single point in manufacture where a panel that has been made correctly can still be ruined. The panel is at its weakest, the mould grips it through suction and mechanical key, and there is no second attempt. Demoulding time also sets how many times a mould can be used in a week, which makes it one of the two or three decisions that actually control a facade programme.
A mould that releases at 16 hours can cast five panels a week. The same mould releasing at 48 hours casts two. On a 400 panel facade that is the difference between eight moulds and twenty.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Demould age, sprayed cementitious panels | 16 to 24 hours | After overnight set, before the moist cure period |
| Strength at demould | Roughly 25 to 40% of 28 day MOR | Enough to carry self weight and handling; typical |
| Demould age, thermoset resin laminate | 4 to 16 hours after lay-up | Once the laminate has cured past green strength; typical |
| Demould age, alpha gypsum | 30 to 90 minutes | Interior gypsum composites set fast |
| Draft angle, rigid moulds | 1 to 3 degrees on vertical faces | Below 1 degree, expect to fight suction; typical |
| Release agent types | Wax, semi-permanent polymer, PVA film, oil emulsion | Matched to mould face and to the coating that follows |
| Suction breaking | Compressed air through mould ports at 200 to 600 kPa | Air is the preferred method; levering is not |
| Handling points | Cast-in lifters or a vacuum frame sized to the green panel | Never lift a green panel on an edge |
When a panel is ready to come off
The answer is a strength, not a clock reading, and the clock is only a proxy for it. A cast panel can be demoulded when it can carry its own weight over the span between its lifting points, resist the peel forces of separation, and take the handling that follows, all without cracking or permanent deformation. For sprayed glass fibre reinforced concrete (GRC, GFRC) that point is normally reached overnight, at 16 to 24 hours, with perhaps a quarter to two fifths of the modulus of rupture that the panel will have at 28 days.
That figure is low enough that panel geometry matters more than material grade. A flat panel with shallow ribs is far more vulnerable at demould than a deeply folded one, because the folds are stiffening. Large flat panels are demoulded onto a frame or turned with a tilting mould rather than lifted free.
Temperature moves the time. A cold shop slows hydration and pushes demould out; heated moulds or an accelerating admixture pull it in. For thermoset resin laminates the equivalent variable is catalyst dose and ambient temperature, and the panel is normally left in the mould until it is dimensionally stable, then post-cured off the mould. Alpha gypsum interior castings release in under an hour.
Release agents
A release agent is a barrier between the casting and the mould face. It must release reliably, leave nothing on the panel that a subsequent coating or sealer will reject, and not attack the mould. The main families are paste and liquid waxes, semi-permanent polymer release systems that bond to the mould and give many releases per application, sacrificial PVA films that transfer and wash off, and oil or oil emulsion agents on steel and timber moulds.
The two failure modes are opposite and both common. Too little release agent, or an agent that has been worn through in a high friction corner, and the panel bonds locally and tears on release. Too much, or an agent that is incompatible with the finish, and the agent transfers to the panel face and shows up later as patchy colour, as a resist under an anti-graffiti coating, or as a bond failure under a sealer. Release agent selection belongs in the quality control plan and is checked on the control sample, not discovered on production panel forty.
Suction, draft and geometry
The force resisting release is rarely adhesion alone. It is mostly suction: as the panel starts to lift, a vacuum forms in the gap and atmospheric pressure holds the panel down. On a large flat face that is a very large force, and it is broken with air rather than with muscle. Moulds for flat or shallow panels are built with air ports so compressed air can be introduced at the interface to break the seal progressively from one edge.
Draft angle is the geometric answer. One to three degrees of taper on faces parallel to the withdrawal direction means the panel separates immediately rather than sliding against the mould for its full depth. Zero draft is workable in a flexible liner and is a problem in a rigid mould. Negative draft, an undercut, cannot be demoulded from a rigid one-piece mould at all, which is where split moulds, flexible liners and lost formwork come in.
Damage modes
- Corner and edge chipping: the most common, and usually a handling problem rather than a strength problem
- Cracking across the panel: green strength was insufficient, or the lift points were wrong, or the panel was levered rather than air released
- Surface pull-off and tearing: release agent failure, worn semi-permanent coating, or a mould face that has lost its gloss
- Distortion and spring: thin panels released before they are dimensionally stable, particularly resin laminates that are still warm
- Mould damage: prising with steel tools damages the mould face, and every subsequent panel inherits the mark
Almost all of these are recorded as panel defects and almost all of them originate in mould design or in the demould method statement. A rejected panel at demould also loses a mould cycle, so the programme cost is larger than the panel cost.
Why demould time drives the programme
Halving the demould age nearly halves the mould count for a given programme, which has a direct effect on tooling cost, on floor area and on lead time. This is why manufacturers invest in heated moulds, accelerated mixes and tilting mould frames, and why a design that reduces the number of distinct mould types, by repeating geometry or by using a single mould with removable inserts, buys more programme than almost any other design decision on a facade package.
Standards and references
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products (demould age, handling and curing sequence)
- BS EN 1169 Precast concrete products, General rules for factory production control of glass-fibre reinforced cement
- AS 3610 Formwork for concrete, surface finish classes and formwork face requirements
- AS 3850 Prefabricated concrete elements, for lifting insert design and safe handling of precast elements
- Release agent manufacturer data sheet, including compatibility with the specified finish and any subsequent coating
- ASTM D2471 (gel time and exotherm) where demould timing of thermoset laminates is being set
Related terms
Questions specifiers ask
How soon can a GRC panel be demoulded?
Normally 16 to 24 hours after casting, once it has enough strength to carry its own weight and the handling that follows. The moist cure period begins after demoulding, not before.
What strength does a panel need at demould?
Roughly a quarter to two fifths of its 28 day modulus of rupture is typical, but the governing check is the panel spanning between its lifting points under self weight, which depends on geometry as much as on the mix.
Why do panels stick even with release agent on?
Usually suction rather than adhesion. Atmospheric pressure holds a large flat panel against the mould as soon as a gap starts to form, which is why moulds are built with air ports to break the seal.
What draft angle should a mould have?
One to three degrees on faces parallel to the direction of withdrawal for a rigid mould. Zero draft needs a flexible liner and negative draft needs a split or sacrificial mould.
How does demoulding affect the project programme?
Demould age sets the mould cycle time, and cycle time sets how many moulds a project needs. A slower release means more moulds, more tooling cost and a longer lead time for the same delivery date.
Panel geometry drives mould count and mould count drives programme. Send your facade geometry early and we will tell you what it costs in cycles. Talk to the ShapeShift team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.