Fibre Reinforced Facade Encyclopedia: Materials
Architectural precast is precast concrete produced to a controlled visual standard, where colour, texture, form and face tolerance are specified alongside structural performance. The distinction from structural precast is not the concrete but the acceptance criteria: an architectural panel is judged on how it looks at a stated viewing distance, which changes the mix design, the mould, the curing regime, the handling and the inspection regime from the first batch onward.
A 150 mm architectural precast panel weighs about 360 kilograms per square metre. Panel size is therefore set by the crane and the truck, not by the material, which is why elevations are usually rationalised into repeating storey height units.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Panel thickness | 100 to 200 mm typical facade | Thicker for load-bearing or deeply modelled units |
| Weight | 250 to 500 kg/m² | Add insulation and inner leaf for sandwich panels |
| Compressive strength | 40 to 50 MPa | Higher than the structural minimum for durability and handling |
| Cover to reinforcement | 30 to 45 mm | Exposure classification dependent under AS 3600 |
| Practical panel size | Up to about 3.5 by 12 m | Governed by transport width and crane capacity |
| Face dimension tolerance | Typically plus or minus 3 to 6 mm | Tighter than structural precast |
| Bowing and warping tolerance | Typically span over 360 | Agree the figure before production starts |
| Pigment dosage | 1 to 6% by weight of cement | Integral colour; white cement for pale shades |
| Finish | Off-form, acid etched, sandblasted, exposed aggregate or polished | Taken from mould and mix, not from a coating |
What makes precast architectural
Three decisions separate an architectural panel from a structural one. The mix is designed for appearance as well as strength, which usually means a single cement source, a single sand and aggregate source, a controlled water to cement ratio and, where colour is required, oxide pigment and often white or off-white cement. The mould is built for a face, with joints, chamfers and reveals detailed to avoid grout leakage and to release cleanly. And the acceptance criteria are visual, defined against an approved sample range rather than a tape measure alone.
The consequence is that materials must be reserved for the whole job at the outset. Cement colour varies between batches and plants, sand varies between pit faces, and a facade cast over six months from two cement sources will show it. The colour consistency entry covers how that is controlled.
Finishes
- Off-form: the face as cast, taking its texture from the mould material, from steel and plywood to polyurethane formliner
- Acid etched: a light wash that removes surface paste to expose fine sand, giving an even matt texture
- Sandblasted: light, medium or heavy, exposing progressively more aggregate and softening colour
- Exposed aggregate: retarder applied to the mould face and the surface washed off, revealing the coarse aggregate
- Polished and honed: ground back to a dense, reflective surface showing full aggregate
- Formliner, reconstructed stone, brick and tile face: profile or a second material cast into the panel face
Every one of these is decided by the mix and the mould rather than applied afterwards, which is the defining characteristic of the material. A change of finish is a change of mix design, since the depth of etch or blast determines how much aggregate is revealed and therefore what the panel colour becomes.
Tolerances and mock-ups
Architectural precast is specified against a range rather than a single sample, because natural variation in cement, sand and aggregate is real and cannot be legislated away. The correct process is a set of sample panels establishing the acceptable range of colour and texture, followed by a full size mock-up including a joint, a corner and a fixing, approved on site under daylight at the stated viewing distance. That approved mock-up becomes the acceptance benchmark for the production run.
Weight and its consequences
At 250 to 500 kilograms per square metre, architectural precast loads the frame, the foundations and the crane schedule. Panel size is limited by what can be transported without escort and lifted at the available radius, so elevations are rationalised into repeating units and the joint pattern becomes an architectural decision driven by logistics.
That weight buys robustness, acoustic mass, thermal mass, and the option of a load-bearing or sandwich panel that carries insulation and an inner leaf in one element. Where the structure cannot carry it, the thin section cementitious alternatives are glass fibre reinforced concrete at 30 to 50 kilograms per square metre and ultra high performance concrete at 60 to 110, both covered in their own entries.
Weathering and maintenance
Concrete weathers, and architectural precast weathers visibly because the face is the finish. Efflorescence appears on new panels as soluble salts migrate to the surface, crazing shows as a fine map pattern in dense paste surfaces, and dirt collects wherever water runs across a face rather than dripping clear. Almost all of this is detailing: drips under sills and copings, throats at reveals, falls that shed water away from the face, and joints that do not discharge run-off onto the panel below.
Penetrating hydrophobic treatments reduce water uptake and dirt pick-up without forming a film, and are commonly specified for panels in exposed positions. Film forming sealers are best avoided on a face that is expected to breathe. The efflorescence and weathering entries cover the mechanisms and the remediation options.
Standards and references
- National Precast Concrete Association Australia, Precast Concrete Handbook
- AS 3600 Concrete structures
- AS 3850 Prefabricated concrete elements, parts 1 and 2
- PCI MNL-117 Quality Control for Architectural Precast Concrete Products
- PCI MNL-122 Architectural Precast Concrete
- AS 1530.1 combustibility; NCC 2022 Volume One Specification 7 (check the edition adopted in your jurisdiction)
Related terms
Questions specifiers ask
What is the difference between architectural and structural precast?
The acceptance criteria. Structural precast is judged on strength and dimension; architectural precast is additionally judged on colour, texture and face tolerance against an approved sample range, which changes the mix, the mould and the inspection regime.
How is colour controlled in architectural precast?
By reserving a single source of cement, sand and aggregate for the whole job, weighing pigment accurately, holding the water to cement ratio constant, and assessing production against an approved range of samples rather than a single chip.
How heavy are architectural precast panels?
Around 250 to 500 kilograms per square metre for panels 100 to 200 mm thick. That governs crane selection, transport and the structural frame, and is the usual reason projects look at thin section alternatives.
Is architectural precast non-combustible?
Concrete is a cementitious material with no polymer matrix, so a product can be tested to AS 1530.1 and classified accordingly. The classification still belongs to the tested product, and any insulation or inner leaf in a sandwich panel has to be assessed separately.
Can architectural precast be curved?
Single curvature is routine, with the mould built to the radius. Double curvature is possible but expensive, because each unique panel needs its own mould, which is the point at which lighter moulded materials are usually considered instead.
Where panel geometry or structural weight rules out precast, ShapeShell-RC delivers the same cementitious surface at 30 to 50 kilograms per square metre. See ShapeShell-RC specifications
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.