Fibre Reinforced Facade Encyclopedia: Manufacturing
Mould making is the production of the negative form that a panel is cast or laminated against, whether that panel is glass fibre reinforced concrete (GRC, GFRC), glass fibre reinforced gypsum or fibre reinforced polymer, and it is the single decision that sets the shape, the surface and most of the cost of an architectural composite package. Called mold making in North America, the craft is the same. Every millimetre of geometry, every texture and every blemish on the mould face is reproduced on the finished panel, so the mould is not a consumable detail of the process; it is the master of record for the panel.
A single GRP mould taken off a polished master will produce 50 to 200 panels. A CNC milled foam mould for a one-off double curved element may produce one.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Mould life, timber and MDF | 5 to 20 pulls | Sealed, filled and waxed face; flat and single curved work |
| Mould life, GRP mould | 50 to 200 pulls | Laminated off a master; gel coated tooling face |
| Mould life, silicone rubber | 20 to 60 pulls | Deep relief, undercuts and texture |
| Mould life, CNC milled foam | 1 to 10 pulls | Coated and faired foam; one pull if left uncoated |
| Mould life, steel | 500 plus pulls | Long production runs of a single repeated unit |
| Draft angle | 1 to 3 degrees per vertical face | Zero draft needs a split mould or a flexible insert |
| Mould tolerance | plus or minus 1 to 2 mm over 3 m | Held tighter than the panel tolerance it produces |
| Shrinkage allowance | 0.1 to 0.3 percent for GRC, 0.2 to 0.6 percent for polyester FRP | Added to mould dimensions before cutting |
| Lead time | 1 to 6 weeks per mould | Pattern, mould, trial pull and sign-off |
| Tooling share of cost | 20 to 40 percent of a low repetition package | Falls sharply once a mould is reused |
What the mould has to do
A mould does four things at once. It holds the geometry to tolerance while the material is wet, it releases the panel without damage, it survives being used again, and it presents a face of the right texture and gloss. These pull against each other. A polished mould gives the best surface but shows every scratch and needs the most careful release. A flexible mould releases the deepest undercut but distorts under the weight of wet material unless it is supported in a rigid backing case.
Because the mould is the master, quality control starts there. A mould that is 3 mm out of square produces panels that are 3 mm out of square for its whole life, and the error is only discovered on site when panels are set out against a grid. Mould dimensions, diagonals and profile are checked and recorded before the first pull, not after.
Mould types and how they are chosen
- Timber, MDF and plywood: cheap and fast for flat, folded and single curved panels; the face must be sealed and waxed because moisture from the mix swells the substrate
- GRP (fibre reinforced polymer) moulds: laminated onto a machined or hand faired master, gel coated and polished; the standard choice for repetition and for compound curvature
- Silicone and polyurethane rubber: cast against a master to reproduce deep texture, sharp relief and undercuts that a rigid mould cannot release
- CNC milled high density foam or polystyrene: cut directly from the model, faired and coated; the fastest route to one-off double curvature
- Steel and aluminium: used where a single unit repeats hundreds of times and dimensional stability over a long run justifies the tooling cost
Most facade packages mix types. A run of 400 identical spandrel units is tooled in GRP; the eight unique corner units on the same building are milled in foam. Where the geometry is milled rather than built by hand, the workflow overlaps with CNC formwork and digital fabrication, and the model that drives the cutter is the same model the shop drawings are taken from.
Draft, undercuts and split lines
Draft is the taper on a face that lets the panel lift off. Without it, the panel locks onto the mould and either the panel or the mould breaks. One to three degrees on each vertical face is normal, and a designer who wants a truly vertical return has to accept either a split mould, a loose insert that comes away with the panel and is removed afterwards, or a rubber face that stretches over the undercut.
Split lines are where the mould comes apart. They leave a witness mark on the panel, so they are placed deliberately at an arris, a rebate or a joint line rather than in the middle of a visible face. Agreeing split line positions with the architect at shop drawing stage avoids a dispute about a faint line on a feature panel once 200 of them are cast.
Shrinkage, the trial pull and the first article
Cementitious and polymer materials both change dimension as they cure, so the mould is made slightly larger than the required panel. GRC shrinkage is small and mostly drying related; polyester and vinyl ester laminates shrink more on cure and continue to move slightly as the resin post cures. The allowance is applied to the mould, not corrected on the panel afterwards.
The first pull off any new mould is a trial, not a product. It is measured against the model, checked for surface defects, blowholes, fibre print through and release marks, and used to confirm the finish against the signed control sample. Only after that is the mould released to production. On a package with a hold point, that first article is often the panel presented for approval.
Tooling cost and repetition
Tooling is a fixed cost spread across the number of panels drawn from it. A facade rationalised into 12 mould types across 900 panels is dramatically cheaper than one with 300 unique panels, even when the two look similar in elevation. This is the practical lever an architect has over the cost of a complex facade: not simplifying the geometry, but arranging it so that curvature repeats.
Standards and references
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products, sections on moulds and demoulding
- BS EN 1169, factory production control for glass fibre reinforced cement
- PCI MNL-128 Recommended Practice for Glass Fiber Reinforced Concrete Panels, mould and tolerance provisions
- ISO 12215 and ISO 14125, laminate property testing used to qualify tooling laminates
- AS 3610 formwork for concrete, for surface finish classes where an off-form finish is specified
- Mould release agent and tooling gel coat manufacturers’ technical data sheets for cure schedules and pull counts
Where this matters on a ShapeShift project
One Sydney Harbour, Barangaroo: A facade of moulded, three-dimensional panels rather than flat sheet, where the tooling strategy and the number of distinct mould types govern both the programme and the cost.
Related terms
Questions specifiers ask
How many panels can one mould produce?
It depends on the mould material. A gel coated GRP mould will typically give 50 to 200 pulls, a timber or MDF mould 5 to 20, a silicone rubber mould 20 to 60, and a milled foam mould between one and ten. Steel tooling is used where the count runs into the hundreds.
Does the mould have to match the panel finish?
Yes. The mould face is reproduced on the panel one to one, including gloss, texture, tool marks and repairs. A textured or exposed aggregate finish is created in the mould and the mix, not applied afterwards, which is covered on the surface finish page.
Can a panel have no draft at all?
Only with a split mould, a loose insert that releases with the panel, or a flexible rubber face. Each adds cost and leaves a witness line, so vertical returns are agreed early rather than assumed.
Who owns the moulds after the project?
Whoever the contract says. It is worth settling, because retaining the moulds is the only economical way to produce a matching replacement panel years later. Otherwise a single damaged panel requires new tooling.
How long does a mould take to make?
One to six weeks, depending on type and size. A milled foam mould can be cut in days once the model is released; a GRP mould needs a master to be made and cured first, then the mould laminated, cured and polished.
Working out how many mould types your facade really needs? We tool GRC, GRG and FRP panels from CNC cut masters and can rationalise geometry before pricing. Talk to our fabrication team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.