A GRC specification that a fabricator can price without a dozen RFIs answers ten questions: panel size, shape, thickness and build, fixing type, substrate, finish, colour, tolerance, movement, and fire pathway. Most specifications answer four of them and leave the rest to be discovered.
This is the checklist we would want to receive. It is written for architects and specifiers working on a GRC or GFRC facade package in Australia, and it assumes you have already settled that GRC is the right material rather than precast, fibre cement or a composite.
1. Panel size, and what really sets it
Panel size is the first cost lever and it is rarely set by the material. It is set by the transport envelope, the crane, the access to the face, and the fixing strategy. Larger panels mean fewer joints, a cleaner reading and faster installation, but heavier picks and less tolerance for site error.
Nominate an indicative panel size and say what is driving it. If the driver is the joint pattern, say so, because the fabricator can often meet the visual intent with a different panel module.
2. Shape and geometry
Flat, single curved, double curved, faceted, or profiled. Each is a different mould strategy and a different cost. Where a shape repeats, say how many times, because repetition is what amortises tooling. A geometry used once and a geometry used ninety times are priced very differently even if the drawing looks the same.
3. Thickness and build
GRC is a skin, not a solid. The panel is a thin shell, usually stiffened by ribs or a frame, and the thickness quoted in a specification should be the shell thickness, with the stiffening described separately. A specification that calls up a solid thickness is describing precast, not GRC, and will be priced as such.
4. Fixing type and the substrate behind it
The fixing decides more about the facade than the panel does. Nominate the supporting structure, the tolerance available at the interface, and whether fixings may be visible. Concealed fixings, adjustable fixings and a defined take up allowance are all cheaper to decide now than to resolve on site.
5. Finish
Off form smooth, acid etched, sandblasted, polished, ribbed, profiled or textured from the mould. Finish affects the mould, the reject rate and the colour consistency, so it belongs in the specification rather than in a later selection. See colour and surface finishes for the range.
6. Colour, and how it will be approved
GRC colour comes from the mix, the aggregate and the finish, not from paint. That gives depth and durability, and it also means colour is approved against a physical sample, never a screen or a printed swatch. Specify sample size, how many, and who signs. An A4 sample and a full panel sample tell you different things.
7. Tolerance, and whose tolerance governs
State the manufacturing tolerance you require and, more importantly, the tolerance of what the panel meets. A facade panel made to tight tolerance fixed to a structure built to looser tolerance produces a joint that varies. Resolve the tolerance stack in the specification, not in an RFI.
8. Movement and joints
Joint width, sealant type, backing rod, and whether the joint is a design feature or something to be minimised. Thermal and moisture movement of the panel and differential movement of the structure both need somewhere to go.
9. Fire pathway
State the building class, rise in storeys and whether the external wall must be non combustible. GRC is a cementitious material tested for combustibility under AS/NZS 1530.1, so it is usually the material that keeps a facade on the deemed to satisfy pathway. Call up the requirement and the evidence you expect, not just a product name. Our material fire rating and test data page sets out what to ask for.
10. Programme
Design freeze, sample approval, first delivery and practical completion. Tooling sits on the critical path for bespoke geometry and cannot start until the geometry is frozen, so the design freeze date is the one that matters most.
A specification skeleton you can adapt
| Clause | What to state |
|---|---|
| Material | Glass reinforced concrete (GRC), also referred to internationally as GFRC. Manufacturer and product name, or performance equivalent. |
| Panel type | Shell with stiffening frame or ribs. Nominal shell thickness. Do not specify a solid section. |
| Size and module | Indicative maximum panel size and the joint module. State what governs it. |
| Geometry | Flat, single curved, double curved, profiled. Number of repeats per unique geometry. |
| Finish | Named finish plus reference sample. Sample size and approval process. |
| Colour | Approved against physical sample. Tolerance for colour variation across the elevation. |
| Fixings | Type, concealed or exposed, adjustability, supporting structure, interface tolerance. |
| Joints | Nominal width, tolerance, sealant and backing specification. |
| Tolerance | Manufacturing tolerance and the tolerance of the interfacing structure. |
| Fire | Building class, rise in storeys, non combustibility requirement, evidence required. |
| Testing and QA | Test reports required, quality system, dimensional verification method. |
| Programme | Design freeze, sample approval, first delivery, completion. |
Five specification errors that cost the most
- Specifying a solid thickness. GRC is a shell. A solid thickness call up gets priced as precast, and the weight assumption flows into the structural design.
- Approving colour from a render. Colour lives in the mix and the finish. Every approval that is not against a physical sample is a variation waiting to happen.
- Leaving the fixing to the fabricator without stating the structure. The fixing cannot be designed without knowing what it fixes to and how accurately that thing will be built.
- Ignoring repetition. Tooling cost is per unique geometry. Rationalising ninety panels into six unique shapes usually saves more than any other single decision.
- Naming a product instead of a requirement on fire. Certifiers assess evidence against a requirement. State the requirement and ask for the report.
What to send when you go out to price
- Elevations and sections, and the 3D model if there is one.
- Approximate area in square metres and the panel count, if known.
- The joint module or the visual intent for joints.
- Building class, rise in storeys and the fire requirement.
- Supporting structure type and the tolerance it will be built to.
- Finish and colour intent, with any adjacent material the facade must sit against.
- Programme dates, especially design freeze.
That package gets a priced response with the assumptions stated. Anything less gets a rate per square metre with a page of qualifications, which is not a price you can compare.
Related reading: GRC and GFRC panels, what actually drives GRC panel cost, and GRC compared with precast concrete.
Frequently asked questions
What thickness should I specify for GRC cladding?
Specify the shell thickness and describe the stiffening separately, because GRC is a thin shell stiffened by ribs or a frame rather than a solid section. Specifying a solid thickness describes precast and will be priced and weighed as precast.
How is GRC colour approved?
Against a physical sample. Colour comes from the mix, the aggregate and the finish rather than from paint, so it cannot be assessed from a render or a printed swatch. Specify the sample size, the number of samples and who signs off.
Does panel size change the price much?
Yes, but not always in the direction people expect. Larger panels reduce joint count and installation time but increase crane and transport cost. The bigger lever is usually repetition: reducing the number of unique geometries reduces tooling, which is where bespoke GRC cost concentrates.
Is GRC suitable for a building that requires non-combustible external walls?
GRC is a cementitious material and is tested for combustibility under AS/NZS 1530.1. Where it passes, it is non-combustible and can be used on external walls requiring non-combustibility. Ask for the specific test report for the product being specified.
When should the fabricator be involved?
Design development, before the geometry and the structural grid are frozen. Panelisation, mould strategy and fixing approach are much cheaper to resolve while the design can still move.
Terms explained
Short definitions of the terms on this page, in our facade materials encyclopedia.
