GRC, FRP and GRG are three different fibre reinforced materials that get specified interchangeably and should not be. GRC is cement based and non-combustible, for external facades. FRP is a polymer composite, the lightest and the sharpest in detail, for sculptural and long-span work. GRG is gypsum based, for interiors where the finish has to be seamless. Choosing between them is usually settled by two questions: is the element inside or outside, and what does the fire pathway require.
| GRC, ShapeShell-RC | FRP, ShapeShell-RT | GRG, ShapeShell-RG | |
|---|---|---|---|
| Matrix | Portland cement and fine aggregate | Polyester thermoset resin | Gypsum |
| Reinforcement | Alkali-resistant glass fibre | E-glass reinforcement fabrics | Chopped glass fibre |
| Process | Sprayed or cast into moulds | Vacuum infusion and resin transfer moulding | Gypsum and fibre slurry cast into moulds |
| Weight | Light for concrete, around half of precast | Lightest of the three | Light, interior scale |
| Fire | Non-combustible to AS 1530.1 | Polymer composite, assessed on reaction to fire rather than non-combustibility | Gypsum carries inherent fire resistance; internal lining evidence applies |
| Where it belongs | External facades, soffits, screens, planters, wet areas | Sculpture, public art, long spans, deep relief, weight-critical elements | Interior walls, ceilings, bulkheads, feature elements |
| Also called | GFRC, glass fibre reinforced concrete | Fibreglass, fibre reinforced polymer | GFRG, glass reinforced plaster |
GRC: the external default
ShapeShell-RC is glass reinforced concrete, known internationally as GFRC. Alkali-resistant glass fibre is distributed through a cement and fine aggregate matrix, which is why the panel works at 15 to 25 mm where a reinforced precast element needs 100 mm or more. There is no steel, so there is no cover requirement and no corrosion mechanism, which is the reason it dominates marine and coastal facades.
Specify GRC when the element is outside, when it needs to read as concrete or stone, when the wall has to be non-combustible, or when the element will sit in a wet or permanently damp condition such as a planter. ShapeShift rates it at around 50 per cent lighter than precast concrete and around 50 per cent stiffer than standard GFRC.
Its limit is detail resolution at small scale and its weight relative to FRP. A 3 m sculptural element with 10 mm returns and knife edges is FRP work, not GRC work.
FRP: the lightest and the sharpest
ShapeShell-RT is fibre reinforced polymer, built from E-glass reinforcement fabrics in a polyester resin matrix and manufactured by vacuum infusion and resin transfer moulding. A flow medium is incorporated in specific laminates so the resin distributes uniformly through the fabric, which is what gives a consistent laminate rather than resin-rich and resin-starved zones. ShapeShift rates it at five times the strength of aluminium with a high strength-to-weight ratio.
Specify FRP when weight is the binding constraint, when the geometry is sculptural, when spans are long and unsupported, or when the element needs crisp arrises and fine detail that a cementitious material cannot hold. It is the material behind most public art fabrication and most feature elements that cantilever.
Its constraint is the one that matters most in Australia: it is a polymer composite, so it is not a non-combustible material. Fire performance is assessed on reaction-to-fire measures rather than non-combustibility, and on any project where the external wall has to be non-combustible, FRP is either the wrong material or needs a Performance Solution. Do not carry an FRP laminate into a specification on the strength of a GRC fire report.
GRG: the interior finish material
ShapeShell-RG is glass reinforced gypsum, also called GFRG or glass reinforced plaster. High-quality gypsum is mixed with water and chopped glass fibre into a slurry and cast into moulds. Gypsum gives the smooth finish and the inherent fire resistance; the glass fibre reduces brittleness and adds the flexibility that lets the material take architectural form rather than flat sheet.
Specify GRG for interior walls, ceilings, bulkheads and feature elements where the joint line has to disappear. It is the material for a curved plaster ceiling that reads as one surface. It is not an external material and it is not for wet areas, and specifying it outside is the single most common substitution error in this family.
The fire distinction that decides most projects
These three materials do not share a fire pathway, and treating them as one family is where specifications get into trouble.
- GRC is cement based and is classified non-combustible when tested to AS 1530.1. That keeps an external wall on a straightforward compliance route.
- FRP has a polymer matrix. Non-combustibility is not the right question for it. The relevant evidence is reaction to fire, heat and smoke release and ignitability for the specific laminate.
- GRG is gypsum based, and gypsum carries inherent fire resistance. For an internal lining the evidence required is different again from an external wall.
In all three cases compliance is assessed on the complete assembly rather than the panel: backing wall, supports, insulation, cavity treatment, fixings, sealants and coatings. ShapeShift publishes independently tested fire performance data for ShapeShell-RC and ShapeShell-RT on its material fire rating page, and the specification should call for the test report matched to the product supplied rather than a claim in a brochure.
Weight, and what it buys
All three are light compared with the materials they replace, and the saving does not show up in the panel line of the estimate. It shows up in the supporting steel, the fixing schedule, the crane class, the number of panels per truck and the rate of install. On a tower or a retrofit over an existing structure, that chain is usually what decides the material, not the rate per square metre.
Ranked lightest first: FRP, then GRG at interior scale, then GRC. Ranked by external durability: GRC, then FRP, then GRG which does not go outside at all.
Geometry and finish
Every one of the three is cast against a mould, so the mould face becomes the finish and the cost sits in the pattern work rather than in the material. What differs is what the material will hold.
- GRC takes double curvature, deep relief and perforation at facade scale, and finishes in through-pigmented colour, textured mould faces, coatings including fluoropolymer and gel coat systems, or bonded stone. Options are set out on the colour and surface finish page.
- FRP holds the sharpest detail and the thinnest returns, and takes gel coat finishes in effectively any colour and gloss level.
- GRG gives the finest surface of the three straight off the mould and is designed to be jointed and finished so the surface reads as continuous plaster.
Where each one gets specified
| Application | Material |
|---|---|
| External facade cladding and rainscreen | GRC |
| Non-combustible external wall requirement | GRC |
| Soffits, spandrels and external screens | GRC |
| Planters, terraces and permanently damp elements | GRC |
| Public art, sculpture and building artwork | FRP |
| Long span or cantilevered feature elements | FRP |
| Weight-critical retrofit where even GRC is too heavy | FRP |
| Complex formwork for in-situ concrete | FRP or GRC depending on reuse |
| Interior ceilings, bulkheads and curved plaster | GRG |
| Interior feature walls in dry areas | GRG or GRC depending on finish |
| Interior linings in wet or high-traffic areas | GRC |
| Benchtops and silica free surfaces | GRC |
Four specification mistakes worth avoiding
- Writing GRC and meaning GRG. If the description is a seamless internal ceiling, the material is gypsum based, and the substitution changes the fire pathway and the warranty.
- Carrying a GRC fire report onto an FRP element. Different matrix, different test, different compliance argument.
- Specifying a rate before rationalising panel types. Mould count drives cost in all three materials. Thirty unique panel types is a different job from eight, at the same area.
- Leaving movement out of the joint design. All three move with temperature and, for the cementitious materials, moisture. Joint design is where thin-section facades succeed or fail.
Project evidence
The distinction between these materials is easiest to see where the same company used both on one building.
- Victoria Pride Centre: GRC for the exterior arched vaults, reinforced thermoset for the lobby egg. The same building, the selection made on where each element sits rather than on preference.
- Little Saigon Welcome Arch: a glass-carbon hybrid composite replacing an originally specified clad steel structure, with the shell carrying the load instead of sitting on a frame.
- RMIT Penrose Building: freeform thermoset where no panel geometry repeats anywhere in the facade, which removes mould reuse entirely.
- Sydney Opera House Concert Hall: 18 acoustic reflectors where stiffness at very low weight was the entire requirement, the case for composites in one object.
Frequently asked questions
Is FRP non-combustible?
No. FRP is a thermoset polymer composite, so non-combustibility is not the applicable measure. Its fire performance is assessed on reaction to fire, heat and smoke release and ignitability, and the report for the specific laminate is what a certifier needs. Where the external wall must be non-combustible, GRC is the material in this family that meets that test.
Can GRG be used outside?
No. GRG is gypsum based and is an interior material. Using it externally is the most common substitution error in this family.
Which is the strongest?
The question depends on the load. FRP has the highest strength-to-weight ratio of the three, which is why it spans and cantilevers. GRC has the greater stiffness and mass at facade scale and handles external exposure. GRG is not a structural material in any of these senses.
Are GFRC and GRC different materials?
No, they are the same material under two naming conventions, GRC in Australia and the United Kingdom and GFRC in North America. The same applies to GRG and GFRG.
Can the three be combined on one project?
Routinely, and most large projects do: GRC on the external facade, FRP for sculptural or weight-critical feature elements, GRG for the interior ceilings. Keeping them in the right places, with the right fire evidence for each, is what the specification has to get right.
Choosing for a live project
The fastest way to settle this on a real job is to send the element, the exposure, the compliance pathway and the structural dead load allowance rather than a request for a rate. Start at contact, or read the background in what is GRC and GRC vs precast concrete panels.
Terms explained
Short definitions of the terms on this page, in our facade materials encyclopedia.
