Fibre Reinforced Facade Encyclopedia: Materials
Glass fibre reinforced gypsum is a composite of high strength alpha gypsum plaster and glass fibre, cast into thin, lightweight panels, domes, columns, vaults and mouldings for interiors. It is paint-ready straight from the mould, takes complex three-dimensional shapes that plasterboard cannot, and is used where a seamless painted finish is wanted on curved or sculpted surfaces.
A ShapeShell-RG panel is cast as a 3 to 6 mm shell and weighs about 23 kg per square metre in service, light enough to fix to standard ceiling and wall framing.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Density | 1,400 to 1,700 kg/m³ | Cast alpha gypsum composite |
| Shell thickness | 3 to 6 mm | Ribbed or returned for stiffness |
| Weight in service | 10 to 25 kg/m² | ShapeShell-RG published value about 23 |
| Flexural strength | 20 to 30 MPa | ShapeShell-RG published value 24 |
| Compressive strength | 40 to 60 MPa | ShapeShell-RG published value 49 |
| Surface | Paint-ready, smooth or textured | Takes primer and paint without skim coating |
| Moisture | Interior use; moisture resistant grades available | Not a wet area or external material |
| Fire | Gypsum based; classified by lining tests | |
| Thermal conductivity | about 2.7 W/m·K as published for ShapeShell-RG |
Where GRG sits
GRG is the interior sibling of GRC. Replace cement with gypsum and the result is lighter, faster to cast, and finished by painting rather than by the mould face. It cannot go outside or into wet areas, and it does not carry the loads GRC does, but for ceilings, domes, column casings, feature walls, light coves and reception desks it produces a seamless sculpted surface that no sheet material can match.
Traditional GRG contains cellulose and is hand cast with variable quality. Modern systems such as ShapeShell-RG use alpha gypsum, glass fibre and polymer additions with no cellulose, and are cast in CNC-milled moulds to a consistent shell thickness.
How it is made
Alpha gypsum is mixed with water and polymer, sprayed or poured into the mould with chopped glass fibre, and allowed to set. Elements are demoulded within an hour or two, trimmed, and dried. Fixing lugs, threaded inserts and steel frames are cast in where the geometry needs them. Joints between elements are filled and sanded on site so the finished surface reads as one piece.
Fire performance
Gypsum is inherently fire resistant because it contains chemically bound water that must be driven off before the material can reach ignition temperatures. GRG products are commonly classified as non-combustible under ASTM E136 or Class A1 under EN 13501-1, and reach the best group number in lining tests, but the classification belongs to the tested product, not the material family.
Where it is used
- Curved and coffered ceilings, domes and vaults
- Column casings, capitals and cornices
- Feature walls, reception desks and joinery faces
- Theatre, hotel and retail interiors where a painted sculptural surface is specified
- Replicating heritage plasterwork
Standards and references
- ASTM C1355 Standard Specification for Glass Fiber Reinforced Gypsum Composites
- ASTM C473 (physical testing of gypsum products)
- ASTM E136, EN ISO 1182 (non-combustibility, where tested)
- AS 5637.1 (group number for internal linings), NCC 2022 Specification 7 (check the edition adopted in your jurisdiction)
- EN 13501-1 (reaction to fire classification, where tested)
Related terms
Questions specifiers ask
What is the difference between GRG and GRC?
GRG uses gypsum plaster as the binder and is for interiors only; it is lighter, quicker to cast and painted on site. GRC uses cement and is used outside, in wet areas and anywhere non-combustibility to AS 1530.1 is required.
Is GRG non-combustible?
Gypsum based products are often classified as non-combustible when tested, but the classification belongs to the specific product. Ask for the test report before relying on the claim.
Can GRG be used in bathrooms?
Standard GRG should not be used in wet areas. Moisture resistant grades exist for humid interiors but external and wet-area applications call for GRC.
How is GRG finished?
It comes out of the mould smooth and paint-ready. Joints are filled and sanded, then the whole surface is primed and painted, giving a seamless result over curved geometry.
How heavy is GRG?
A 3 to 6 mm shell with ribs weighs about 10 to 25 kg per square metre, so it fixes to conventional ceiling grids and wall framing.
Need a sculpted interior surface that reads as one piece? ShapeShell-RG is our GRG system, cast from CNC-milled moulds. See ShapeShell-RG specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.