Fibre Reinforced Facade Encyclopedia: Manufacturing
A laminate is the engineered stack of reinforcement plies and cured resin that forms a fibre reinforced polymer panel, together with the gel coat on its face and any core between its skins. It is the product of hand lay-up or vacuum infusion rather than a process in itself, and it is what a structural engineer actually designs. Two panels of identical thickness and identical appearance can differ in capacity by a factor of three because their laminates differ, which is why FRP is specified by laminate schedule and not by thickness.
A common architectural facade skin reads 600 gsm gel coat, 30 gsm surface tissue, CSM 450, WR 600, CSM 450. That is about 3.5 mm thick and about 6 kg per square metre, and every element of it is there for a reason.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Schedule notation | Reinforcement type plus areal weight in gsm, in build order | CSM 450 is chopped strand mat at 450 g/m2 |
| Chopped strand mat | 225, 300, 450 and 600 gsm | Random in-plane fibre; equal properties in all directions |
| Woven roving | 400, 600 and 800 gsm | Bidirectional; strength concentrated on 0 and 90 degrees |
| Biaxial and quadaxial stitched fabric | 300 to 1,200 gsm | Fibre placed at 0, 90 and plus or minus 45 degrees |
| Gel coat | 400 to 600 micrometres | The weather face; not a structural ply |
| Surface tissue | 30 to 50 gsm | Resin rich barrier that stops fibre print through |
| Single skin facade laminate | 3 to 8 mm | ShapeShell-RT published range |
| Cored or monocoque construction | 10 to 50 mm overall | Stiffness from separation of the skins |
| Glass content by weight | 30 to 45 percent hand laid, 55 to 70 percent infused | Verified by burn-off to ISO 1172 |
| Flexural strength | 150 to 250 MPa | ShapeShell-RT published at 221 to 241 MPa |
Reading a laminate schedule
A schedule lists the plies in the order they go into the mould, starting at the mould face, which becomes the visible outer face of the panel. Each entry names the reinforcement type and its areal weight in grams per square metre. The convention is dense enough that a schedule reads as a recipe: gel coat first, then a fine surface tissue, then the structural plies, then any core, then the plies of the inner skin.
The order matters as much as the content. The tissue immediately behind the gel coat prevents the coarse texture of the structural glass from telegraphing through to the finished face as the resin shrinks on cure. Heavier fabrics are separated by mat plies that improve interlaminar bond. Local reinforcement, extra plies at fixing points, around openings and along returns, is called up on the schedule with its extent, not left to the laminator.
Ply orientation and balance
Chopped strand mat is isotropic in the plane: the fibres are random, so the laminate behaves the same in every direction but uses fibre inefficiently. Woven roving and stitched fabrics place fibre along nominated axes, so a panel can be made stiff in the direction it spans without carrying weight in the direction it does not. Orientations are described relative to the panel’s principal axis as 0, 90 and plus or minus 45 degrees.
Directional laminates should be balanced and symmetric about the mid-plane. A laminate that is not symmetric will warp as it cures and will continue to move with temperature, which on a facade panel shows up as a bowed unit that will not sit flat against its brackets. This is a design decision made on the schedule, not something a laminator can correct.
Cores, skins and where stiffness comes from
FRP has a low elastic modulus, so architectural panels are almost always governed by deflection rather than by strength. Adding resin and glass to a single skin is an inefficient way to fix that. Separating two thin skins with a lightweight core, or folding the skin into returns and ribs in a monocoque panel, multiplies the second moment of area for very little added weight.
- Closed cell PVC and PET foam cores: 60 to 200 kg per cubic metre, the common choice for facade sandwich panels
- End grain balsa: high shear strength, used where local loads are applied
- Honeycomb: the lightest option, but demanding on bonding and on edge closure
- Moulded ribs and returns: stiffness from geometry alone, with no core to detail at the edges
Whichever route is taken, the edges and the fixing points are the detail that matters. A core must be closed out or replaced with solid laminate wherever a fastener passes through, or the fixing crushes the core rather than bearing on the skins.
How a laminate is specified and checked
A specification that names a panel thickness alone is not enforceable. What binds is the laminate schedule, together with the properties it is required to deliver and the evidence that the delivered panels match. A workable set of clauses names the schedule ply by ply, the resin system and any fire retardant additives, the gel coat type and thickness, the core type and density, the target glass content and void content, and the test methods by which each will be verified.
Verification is straightforward and inexpensive. Glass content comes from a burn-off test to ISO 1172 on a coupon cut from a witness panel or from panel flash. Void content follows ASTM D2734. Flexural and tensile properties are measured to ISO 14125 and ISO 527. Degree of cure is confirmed by Barcol hardness to ASTM D2583. Gel coat thickness is measured wet with a comb gauge and dry with a film gauge. Requiring these as recorded production checks, rather than as a one-off type test, is what keeps a long run honest.
Standards and references
- ISO 1172, determination of glass content by burn-off
- ISO 14125 flexural properties and ISO 527 tensile properties of fibre reinforced plastics
- ASTM D2734 void content; ASTM D2583 Barcol hardness
- ISO 12215 and BS EN 13706, laminate specification and profile conventions
- ASTM D3039 and ASTM D790, tensile and flexural testing of polymer matrix composites
- AS 5637.1 group number and AS 5113 full-scale facade test, where the laminate forms part of an external wall (check the edition of the NCC adopted in your jurisdiction)
Related terms
Questions specifiers ask
What does CSM 450 mean in a laminate schedule?
Chopped strand mat with an areal weight of 450 grams per square metre. The number is the weight of dry reinforcement per square metre, not the cured thickness, which for that ply is roughly 1.0 to 1.3 mm hand laid.
Why specify a laminate schedule rather than a panel thickness?
Because thickness says nothing about capacity. Two 5 mm panels can differ threefold in strength depending on fibre type, orientation, glass content and voids. The schedule is what an engineer designs and what a fabricator can be held to.
Does a laminate have to be symmetric?
Directional laminates should be balanced and symmetric about the mid-plane. An unbalanced laminate cures with built-in warp and keeps moving with temperature, which on a facade shows as panels that will not sit flat.
How is a delivered laminate verified?
By coupon testing and recorded production checks: glass content by burn-off to ISO 1172, void content to ASTM D2734, flexural and tensile properties to ISO 14125 and ISO 527, Barcol hardness for cure, and gel coat thickness by film gauge.
Is the gel coat part of the structural laminate?
No. The gel coat is the weather and appearance face, typically 400 to 600 micrometres, and contributes nothing to capacity. It is specified separately for colour, gloss, UV resistance and thickness.
Need an FRP panel engineered to a deflection limit rather than a nominal thickness? ShapeShell-RT is supplied with a documented laminate schedule and published properties. See ShapeShell-RT specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.