Fibre Reinforced Facade Encyclopedia: Materials
Precast concrete panels are reinforced concrete wall units cast in a controlled factory or casting yard, cured, then transported and craned into position on site. They are normally 100 to 200 mm thick and weigh 240 to 480 kg per square metre, and unlike most cladding they can be designed to carry load, which is why precast is used both as a cladding skin and as the structure itself.
A 150 mm precast panel 3 metres wide by 8 metres tall weighs about 8.6 tonnes. The crane, the transport permit and the slab edge that receives it are all sized by that number.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Panel thickness | 100 to 200 mm typical | Up to 300 mm for load-bearing and sandwich units |
| Weight in service | 240 to 480 kg/m² | Concrete density about 2,400 kg/m³ |
| Concrete strength | 32 to 50 MPa characteristic | Higher than in-situ to allow early lifting |
| Reinforcement cover | 25 to 50 mm | AS 3600 exposure class; sets the minimum thickness |
| Panel size | up to about 3 by 12 m | Limited by transport width and crane capacity |
| Thermal conductivity | 1.4 to 1.7 W/m·K | Insulation is separate, or a core in a sandwich panel |
| Thermal mass | about 2,200 kJ/m³·K | The main energy advantage over lightweight cladding |
| Thermal expansion | about 10 x 10⁻⁶ per °C | |
| Fire | Non-combustible and inherently fire resisting | FRL from thickness and cover per AS 3600 Section 5 |
| Service life | 60 to 100 years | Cover, crack control and exposure class dependent |
Types of precast panel
- Cladding panels, non load-bearing, fixed back to a frame and carrying only their own weight and wind load
- Load-bearing wall panels, carrying floor and roof loads as part of the structure
- Shear and core walls, providing lateral stability, common in car parks and low-rise commercial
- Sandwich or insulated panels, two concrete wythes with rigid insulation between them, joined by low-conductivity connectors
- Tilt-up panels, cast flat on the ground slab on site rather than in a factory, then tilted up into place
- Architectural precast, where the finish, profile and colour are specified to an appearance standard rather than a structural one
The distinction between architectural precast and structural precast is one of tolerance and finish rather than material. Architectural precast is made in purpose-built moulds to tighter dimensional and appearance tolerances, often with a selected aggregate, white or off-white cement and a surface treatment, and is priced accordingly.
Why panels are the thickness they are
The thickness of a precast panel is set by reinforcement cover, not by strength. Steel reinforcement corrodes if the alkaline concrete around it carbonates or chlorides reach it, so AS 3600 requires cover of 25 to 50 mm depending on exposure class. With cover on both faces and bar diameter between them, the practical minimum for a reinforced panel is about 100 mm, and 125 to 150 mm is the common cladding thickness.
That is the fundamental difference between precast and the thin fibre reinforced composites. Glass fibre reinforced concrete has no steel and therefore no cover requirement, so the same span can be achieved in a 15 mm skin with ribs. The trade is that the thin skin cannot be load-bearing and precast can. See GFRC versus precast for the comparison in detail.
Manufacture and finish
Panels are cast face down in a steel or timber mould on a casting bed. Reinforcement cages, cast-in ferrules, lifting anchors and any window or service penetrations are placed before the pour. The concrete is placed, vibrated and, on a heated bed or with steam, accelerated so the panel can be lifted the following day. Panels are then stored vertically or in stacks to gain strength before delivery.
The mould face becomes the visible face, so the finish is decided before the pour: off-form against a steel or plywood face, textured against a form liner, exposed aggregate via a retarder and subsequent wash, acid etched, sandblasted or polished after cure, or coated afterwards. Integral colour comes from oxide pigments and the choice of cement. Colour consistency across a facade depends on keeping the mix, the aggregate source, the cure regime and the mould age constant across all pours, which is why architectural precast is normally reserved from a single batch of cement and a single aggregate stockpile.
Fixing, tolerance and erection
Non load-bearing panels are fixed to the structure with cast-in ferrules and bolted angle or plate connections, typically two gravity fixings low on the panel and restraint fixings above, slotted so that the panel can move relative to the frame. Load-bearing panels are grouted into place and connected through starter bars or welded plates, and the joint is designed to transmit vertical and shear load.
Precast is heavy, and its erection sequence, crane placement and temporary propping usually drive the site programme rather than following it. Panels are set out from survey of the completed frame, with dimensional tolerance to AS 3610 and appearance tolerance to the class specified. Erection tolerance is normally plus or minus 10 mm on position, wider than a lightweight panel system, so the joint is sized to suit.
Fire, thermal and acoustic performance
Precast concrete is non-combustible without qualification and does not need a reaction-to-fire classification for that purpose. Its fire resistance level for insulation and integrity is derived directly from thickness and cover under AS 3600 Section 5, and a 150 mm panel with normal cover will comfortably reach an FRL well beyond what most external walls require. This is the clearest advantage precast holds over every lightweight cladding: the wall and its fire rating are the same element.
Thermally, concrete is a poor insulator and an excellent store. Precast contributes high thermal mass, which flattens internal temperature swings and suits climates with a wide diurnal range, but it needs insulation added behind it or built into a sandwich panel to meet NCC Section J. Acoustically, mass is the dominant variable and a 150 mm panel is a very effective airborne sound barrier, which is why precast dominates on rail and road corridors.
Standards and references
- AS 3600 Concrete structures; Section 5 for fire resistance from thickness and cover
- AS 3610 Formwork for concrete, including surface finish classes
- AS 3850 Prefabricated concrete elements (handling, lifting and temporary bracing)
- NPCAA National Precast Concrete Association Australia guidance and Code of Practice
- PCI MNL-117 Manual for Quality Control for Plants and Production of Architectural Precast Concrete
- NCC 2022 Volume One Specification 7 and Section J (check the edition adopted in your jurisdiction); AS/NZS 1170.2 wind actions
- AS 4284 Testing of building facades where the precast forms a tested assembly
Related terms
Questions specifiers ask
How much does a precast concrete panel weigh?
About 240 kg per square metre at 100 mm thickness, 360 kg at 150 mm and 480 kg at 200 mm, based on a concrete density near 2,400 kg per cubic metre. A single 3 by 8 metre panel at 150 mm is roughly 8.6 tonnes.
How thick does a precast panel need to be?
About 100 mm as an absolute minimum for a reinforced panel, because AS 3600 requires 25 to 50 mm of cover over the steel on each face. Cladding panels are commonly 125 to 150 mm; load-bearing and sandwich panels are thicker.
Is precast concrete non-combustible?
Yes. Concrete is non-combustible and precast panels satisfy the NCC’s non-combustibility requirement for external walls directly. Their fire resistance level is calculated from thickness and cover under AS 3600 rather than from a reaction-to-fire test.
What is the difference between precast and tilt-up?
Precast is cast in a factory or dedicated yard and transported to site. Tilt-up is cast flat on the building’s own ground slab and tilted into position on site. Tilt-up avoids transport but gives less control over finish and tolerance, so it is rarely used where appearance is critical.
Can precast panels be used for recladding?
Rarely. An existing structure was sized for its original facade and usually cannot accept 240 to 480 kg per square metre of new load plus the eccentricity of hanging it off the slab edge. Recladding normally uses a lightweight cladding material, most often GRC or a polymer composite.
What finishes are available on precast?
Off-form, form liner textures, exposed aggregate, acid etch, sandblast, polish, and applied coatings. Colour comes from the cement, the aggregate and oxide pigments. Consistency across a facade depends on holding the mix, aggregate source and cure constant across every pour.
Where the structure cannot take precast, or the geometry will not release from a heavy mould, a thin GRC skin does the same job at a fraction of the weight. See ShapeShell-RC specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.