Fibre Reinforced Facade Encyclopedia: Manufacturing
Hand lay-up is the open mould process in which glass reinforcement is placed into a gel coated mould by hand and wetted out with catalysed resin using brushes, rollers and squeegees, ply by ply, until the specified laminate is built. It is the oldest fibre reinforced polymer process and still the dominant one for bespoke architectural FRP, because it imposes almost no limit on geometry and requires only a single sided mould.
A hand laid architectural laminate typically reaches 25 to 35 percent fibre by volume. The same plies infused under vacuum reach 50 to 65 percent, in a thinner and lighter panel.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Fibre volume fraction | 25 to 35 percent | Chopped strand mat laminates sit at the lower end |
| Glass content by weight | 30 to 45 percent | Measured by burn-off to ISO 1172 |
| Void content | 2 to 5 percent typical | Above about 5 percent, strength and durability fall away |
| Laminate thickness per CSM 450 ply | about 1.0 to 1.3 mm | Varies with roller pressure and operator |
| Thickness variation across a panel | plus or minus 10 to 20 percent | The main quality control issue in the process |
| Gel coat thickness | 400 to 600 micrometres | Applied to the mould before the first ply |
| Tooling requirement | Single sided, open mould | No vacuum integrity needed |
| Practical panel size | Limited by mould and handling, not by the process | Layers can be lapped and staged |
| Resin consumption | 2 to 2.5 kg resin per kg of glass | Higher than infusion; adds weight and cost |
How the process runs
The mould is cleaned, waxed or treated with release agent, and a pigmented gel coat is sprayed or brushed onto the mould face and allowed to gel. A resin rich backing layer, usually a fine surface tissue or a light chopped strand mat, goes on next to prevent the coarse reinforcement printing through to the visible face. The structural plies then follow, each one placed dry and wetted out with catalysed resin, then consolidated with a grooved metal or plastic roller that drives resin through the fibre bundles and pushes entrapped air out to the edges.
Consolidation is where the laminate is made or lost. Resin has to reach every filament, and the air introduced by the brush has to be worked out before the resin gels. Once the exotherm starts, nothing further can be corrected. On thick sections the laminate is built in stages so the heat of cure does not distort the mould or crack the gel coat.
Wet-out, voids and fibre volume fraction
Hand lay-up is a wet, low pressure process, so it carries more resin than it strictly needs. The fibre volume fraction that results, commonly 25 to 35 percent, is well below what a closed process achieves. Because the fibre carries the load and the resin mostly holds it in place, a lower fibre fraction means lower stiffness and strength for the same panel thickness, and more weight for the same performance.
Voids are the second penalty. Air trapped between filaments creates stress concentrations, gives water a path into the laminate and reduces interlaminar shear strength. A well consolidated architectural laminate runs around 2 to 3 percent voids; a poorly rolled one can exceed 5 percent, and the difference is invisible from the finished face.
Consistency and quality control
The process is operator dependent, so control is procedural rather than automatic. The practical measures are a written laminate schedule that names every ply by type and weight, pre-cut and nested reinforcement so plies cannot be substituted, resin and catalyst dispensed by metered gun or weighed batch rather than judged by eye, and recorded checks as the panel is built.
- Wet film and cured gel coat thickness, checked with a comb gauge and a dry film gauge
- Ply count and ply orientation logged for each panel against the schedule
- Laminate thickness measured at nominated points, and panel mass weighed against a target
- Barcol hardness on the cured laminate to confirm the resin has reached cure
- Glass content by burn-off on a coupon cut from the flash or from a witness panel
Those records are what let a specifier verify that the delivered panel matches the laminate that was engineered, which is the subject of the laminate page.
Where hand lay-up is the right process
Hand lay-up wins wherever the geometry is complicated, the run is short, or the panel is large and deeply three-dimensional. Sculptural work, one-off facade features, panels with heavy returns, repairs and site made closures are all far easier open moulded than infused. Tooling is cheap, changes are possible mid-run, and a panel can be locally reinforced simply by adding plies where the engineer asks for them.
It loses on repeatability, on weight and on emissions. A long run of identical flat or gently curved panels is a better candidate for vacuum infusion, which produces a lighter, denser and more uniform laminate. Many architectural packages use both: infusion for the repeating field panels, hand lay-up for the corners, soffits and one-off units.
Standards and references
- ISO 1172, determination of textile glass reinforced plastics content by burn-off
- ISO 14125 flexural properties and ISO 527 tensile properties of fibre reinforced plastic composites
- ASTM D2583, Barcol hardness of rigid plastics, used to confirm degree of cure
- ASTM D2734, void content of reinforced plastics
- BS EN 13706 and ISO 12215, laminate specification conventions carried over into architectural work
- Resin, gel coat and catalyst manufacturers’ technical data sheets for cure schedule and exotherm limits
- Safe Work Australia workplace exposure standards for styrene in open moulding
Related terms
Questions specifiers ask
What fibre volume fraction does hand lay-up achieve?
Typically 25 to 35 percent by volume, against 50 to 65 percent for vacuum infusion. The lower figure means a hand laid panel is heavier and less stiff than an infused panel of the same thickness, which the laminate schedule allows for.
Is hand lay-up weaker than infusion?
For the same plies, yes, because it carries more resin and more voids. It is not weak in absolute terms; it is simply less efficient, so an engineered hand laid panel uses a heavier schedule to reach the same capacity.
Why is hand lay-up still used for architectural FRP?
Because it handles geometry that closed moulding cannot, needs only a single sided mould, allows local reinforcement to be added where an engineer asks for it, and suits short runs and one-off panels.
How is a hand laid panel checked?
By recorded process control: gel coat thickness, ply count and orientation, laminate thickness at nominated points, panel mass, Barcol hardness for cure, and glass content by burn-off on a coupon.
Can the two processes be mixed on one facade?
Yes, and it is common. Repeating field panels are infused for weight and consistency while corners, soffits and one-off features are hand laid, provided both are engineered to the same performance and finish.
Specifying an FRP facade or a sculptural element? ShapeShell-RT is our FRP system, laminated from CNC cut tooling with a documented laminate schedule. See ShapeShell-RT specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.