Fibre Reinforced Facade Encyclopedia: Properties
Impact resistance is the energy a material or an assembled panel absorbs before it cracks, punctures or comes away from its fixings. It is measured two ways: on a small coupon by a Charpy or Izod pendulum, which gives a material property in kilojoules per square metre, and on a complete panel by the hard body and soft body tests used for facades, which give a pass or fail against a stated energy.
A soft body facade impact test swings a 50 kg bag into the panel to represent a person falling against it. A hard body test fires or drops a 0.5 or 1 kg steel ball to represent a thrown or dropped object.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Soft body impact, facade | 50 kg bag at 120 J serviceability and 500 J safety | ISO 7892 impact bodies, CWCT criteria |
| Hard body impact, facade | 0.5 kg steel ball at 10 J; 1 kg steel ball at 6 J | ISO 7892 impact bodies |
| FRP laminate, Charpy | 50 to 150 kJ/m² | Typical glass reinforced polyester, ISO 179 |
| Sprayed GRC, Izod | 10 to 25 kJ/m² | Typical range published for sprayed GRC |
| Fibre cement sheet | 2 to 5 kJ/m² | Typical, for comparison |
| Failure mode, FRP | Local star crack or delamination, panel stays in one piece | Fibres bridge the damage |
| Failure mode, GRC | Local crushing and fine cracking, fragments held by fibre | No brittle shatter to loose pieces |
| GRG | Interior use only, 24 MPa flexural, damage repairable in situ | ShapeShell-RG, 3 to 6 mm gypsum shell |
Two different questions
A coupon test answers a material question. A notched specimen is broken by a swinging pendulum, and the energy absorbed, divided by the fracture area, is reported in kilojoules per square metre. Charpy loading under ISO 179 supports the specimen at both ends; Izod under ISO 180 clamps it at one end. The numbers rank materials and serve quality control, and they cannot predict whether a particular panel will survive a trolley hitting it.
A facade test answers the building question. A complete panel, on its real fixings and substructure, is struck with a defined body at a defined energy, and judged on three criteria: no damage affecting appearance at serviceability level, no loss of weathertightness, and nothing detaching that could injure someone below.
Why fibre reinforcement changes the failure mode
Both FRP and glass fibre reinforced concrete (GRC, GFRC) are tough rather than merely strong, and toughness is what matters under impact. In an unreinforced brittle material a crack, once started, runs to the edge of the panel and the piece falls. In a fibre reinforced composite the crack has to pull fibres out of the matrix or break them to advance, which consumes energy over a much larger volume than the crack plane itself.
The practical outcome is that damage stays local and the panel stays attached. A GRC skin struck hard enough will crush and craze at the point of impact, but the glass fibre holds the fragments in place. An FRP laminate shows a star crack or some local delamination and stays in one piece. That is worth more on a public facade than a high headline energy value.
Where impact matters on a building
- The ground plane and any accessible zone, conventionally to about 2 m above a floor, walkway or balcony
- Loading docks, car park entries and back of house areas where trolleys and vehicles come close
- Balustrades and anything a person could fall against
- Soffits, sunshades and low level fins, where maintenance access and ladders are the hazard
- Public art and sculptural elements, which people touch, climb and lean on
- Hail exposed surfaces in the eastern states, where the impact body is small, hard, fast and repeated
Above the accessible zone the soft body case falls away and only hard body impact, generally from thrown objects or hail, remains relevant.
Testing and specifying
ISO 7892 defines the impact bodies and the general procedure for vertical building elements, and the CWCT standard and its technical notes set the energy levels and pass criteria most facade specifications adopt, commonly 120 J soft body for serviceability and 500 J for safety, with 10 J hard body. EN 14019 sets impact classes for curtain walling. In Australia the deemed to satisfy provisions of the NCC contain no impact requirement for cladding (check the edition adopted in your jurisdiction), so the criteria come from the project specification. Name the standard, the impact body, the energy and the acceptance criteria, or the test is not defined.
Damage and repair
All three materials are repairable in place, which is a real advantage over brittle sheet products that have to be replaced. An FRP panel is ground back, re-laminated and recoated, and the repair disappears once the topcoat is applied. A GRC panel is cut back and patched with a matched mix, where the difficulty is colour and texture rather than strength, since a patch cures to a slightly different shade and weathers differently for some years. GRG is filled and repainted like plasterboard.
Keeping spare panels and retaining the mix and batch records decides whether a later repair disappears or stays visible for the life of the building.
Standards and references
- ISO 7892 Vertical building elements, Impact resistance tests, Impact bodies and general test procedures
- CWCT Standard for Systemised Building Envelopes, and Technical Notes on impact performance
- EN 14019 Curtain walling, Impact resistance, Performance requirements
- ISO 179 Charpy impact properties and ISO 180 Izod impact strength of plastics
- GRCA Specification for the Manufacture, Curing and Testing of GRC Products
- AS/NZS 4284 Testing of building facades, which covers structural, air and water performance; impact is by project specification
Related terms
Questions specifiers ask
Is FRP or GRC more impact resistant?
On a coupon, FRP absorbs considerably more energy. On a building both perform well, because the fibre keeps damage local and holds the panel together, which is what the safety criterion measures.
What impact energies should be specified?
A common set is 120 J soft body for serviceability and 500 J soft body for safety, with 10 J hard body, using the ISO 7892 impact bodies. The zone and the energy should be stated in the specification.
Does the NCC require facade impact testing?
Not in the deemed to satisfy provisions for cladding. Impact criteria come from the project specification, usually following the CWCT standard or EN 14019.
Can an impact damaged panel be repaired?
Yes. FRP is ground back, re-laminated and recoated. GRC is cut back and patched with a matched mix, where colour and texture matching is the difficulty. GRG is filled and repainted.
Specifying impact criteria for a public facade or a sculptural element? ShapeShift can advise on panel build up and fixing design for the required energy levels. Contact ShapeShift
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.