Precast concrete offers many different colours and textures, from a basic off-form grey through to a stained formliner finish. Careful selection of finishes can turn a building's design into an award winning aesthetic masterpiece. The finish you are able to achieve may depend on the manufacturer you choose and to an extent, the type of panel. It is not uncommon to have precast elements with more than one finish. Some of the most common finishes are listed below.

Hotel Realm and Capitol Apartments, Canberra	Hotel Realm and Capitol Apartments, Canberra

Caroline Springs Library & Community Centre, Caroline Springs	University of South Australia Hawke Building, Adelaide	Mantra Hotel, Tullamarine

TEXTURES

Off-form
Off-form concrete elements are most commonly produced using grey cement. The high quality of the moulds and the quality assured manufacturing techniques used by National Precast Members mean that the quality of finish is extremely high and generally requires no additional finishes to be applied, other than perhaps stain or paint. For variation, false joints and rebates can be incorporated into designs, or alternately many precast manufacturers are able to include colour pigment into the concrete mix.

The Australian Standard AS3610.1 - 2010, Formwork for Concrete describes the benchmarks for off-form grey concrete. It defines in detail the characteristics of the classes of surface finish with Class 1 being the highest standard and Class 5 the lowest. Class 1 is only recommended for use in very special features of buildings of a monumental nature and must not be specified for whole elevations. Class 2 is the most common specification for high quality architectural precast concrete.

Whilst AS3610 can be used to evaluate the quality of surface and tonal colour range of grey concrete cast against the mould, the standard cannot be directly applied to trowelled surfaces, applied finishes or coloured concrete. For evaluation of these surfaces the Standard requires that samples of the finish and colour are made to manage the quality of finish and the acceptable variations in colour for the project.

University of South Australia Hawke Building, Adelaide	University of South Australia Hawke Building, Adelaide
Berry Sports & Recreational Centre, Berry Photographer: Nic Bailey	Berry Sports & Recreational Centre, Berry Photographer: Nic Bailey

For more information regarding this finish please refer to 10.6.2 of the Precast Concrete Handbook (click here to buy the Handbook), National Precaster Issue 56 or talk to one of our Members.

Case Studies:

The University of SA, Hawke Building, Adelaide

Berry Sports & Recreational Centre, Berry, NSW

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New Guide for Off Form Precast Surface Finishes

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3D Surfaces
Precast concrete elements can be designed and manufactured with 3D surface finishes to achieve unique textures and/or profiles. This can be done using specially made moulds, form liners, tiles, bricks, stone, void formers or by use of other techniques like bush-hammered or hammered-nib applications. An advantage of using a 3D surface pattern that can self-shade a vertical element, thereby reducing thermal conductivity from the sun. With the use of CAD/CAM/CAE technologies the possibilities are endless.

Place on Brougham, North Adelaide	Place on Brougham, North Adelaide
Hedley Bull Centre, Australian National University, Acton, ACT Photographer: Dianna Snape Photography	Hedley Bull Centre, Australian National University, Acton, ACT Photographer: Dianna Snape Photography
Holroyd Gardens Arch, Parramatta, Sydney	Parramatta Rail Station, Parramatta, Sydney

For more information regarding this finish please refer to Chapter 10 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Cast studies:

Hedley Bull Centre, Australian National University, Acton, ACT

Parramatta Rail Station, Sydney

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Etching
Etching refers to a process where about a week after the precast element is removed from the mould, it is washed with an acid solution and the scrubbed to remove the outer skin. The result is a flat, sand-textured surface that resembles limestone or sandstone. The high quality of precast concrete ensures that chloride penetration to the reinforcement is not a risk. A very good off-form surface finish with a minimum of voids required to use this finish successfully.

National Film and Sound Archive, Canberra	National Film and Sound Archive, Canberra

For more information regarding this finish please refer to 10.6.7 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

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Grit (or Sand) Blasting
Grit (or sand) blasting is a technique of abrasive surface preparation using compressed air to propel various particles (e.g. granulated furnace slag, aluminium oxide, glass beads) onto the concrete surface. The process is also referred to bead blasting where larger beads are used.

The surface layer of concrete is removed to expose the aggregates, giving a deeper textured finish. The depth of the grit blasting can be varied to allow a smooth to coarse texture. The aggregate selection, as well as the matrix colour, has a significant effect on the final appearance.

Adelaide Oval, Adelaide	Adelaide Oval, Adelaide

For more information regarding this finish please refer to 10.6.6 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Case studies:

SA Water

Adelaide Oval

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Exposed Aggregate
An exposed aggregate finish removes the top layer of the concrete matrix to expose the top surface of the aggregates in the concrete mix. Chemical retarders are often applied to the surface to etch away the concrete matrix without sacrificing the aggregate. Alternatively a water washing technique may be used. It is often used in conjunction with other finishes.

For more information regarding this finish please refer to 10.6.3 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Case studies:

Menzies School of Medical Research, Hobart, Tasmania

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Honing & Polishing
Honing and polishing are 2 individual surface treatments that can also be combined as a two-step process to give a superior surface similar to natural polished stone or granite. Honing refers to the removal of the outer surface of concrete by using a grinder that has a coarse abrasive effect, exposing the aggregate in the concrete and giving a flat level surface.

Polishing is a similar process taking the finish to the next level, which uses finer abrasive materials to take a finer cut from the concrete. The result is a very smooth, shiny finish. Both processes use lubrication to ensure gouging and scrathcing don't occur on the surface. Aggregates used for honed and polished surfaces are chosen for colour, durability and ability to hold a polish. Polished surfaces shed water and dirt easily and have minimal surface absorption, and therefore require minimal ongoing maintenance. Polishing and honing of curves and small recesses are possible but the shape of the element must be considered for this surface, along with the capability of the individual supplier.

Thebarton Bioscience Building, Adelaide	Thebarton Bioscience Building, Adelaide
Jane Foss Russell Building, University of Sydney	Jane Foss Russell Building, University of Sydney

Case studies:

Top Ryde Shopping Centre, NSW

COLOURS

Integral Colouring
The colouring of concrete is achieved through the use of cements, coloured sands, coloured aggregates and pigments (oxides). The basic cements used are grey, off-white and white. The use of cement colour will depend on the final colour choice, with grey cement generally used for darker colours moving to white cement for light colours. The use of coarse aggregates will have more impact visually because of their size. When an exposed finish is selected such as grit (sand) blasting or polishing, the coarse aggregates will have the most significant impact visually because of their predominance and sand colour will alter the colour of the surrounding cement matrix. Where the desired colour cannot be achieved by using cement, aggregate and sand selection, a wider range of colour can be achieved using pigments (oxides). Coloured precast elements can also have other finishes applied to them like etching, grit blasting, water washing, polishing and honing if requested.

Taronga Zoo Elephant Enclosure, Sydney	Taronga Zoo Elephant Enclosure, Sydney
Channel 10, Adelaide	Channel 10, Adelaide

For more information regarding this finish please refer to 10.5 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Case studies:

Taronga Zoo, Sydney

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Staining
Unlike paint that is a surface coating, stain is absorbed into the concrete surface. The colour palette is almost infinite, but is usually based around natural colours and is generally guaranteed for 25+ years on vertical surfaces before the finish starts to fade. Colour matching is also available with staining. Stains can be translucent or opaque and are often combined with the use of form liners (see 3D Surfaces) for a very broad combination of aesthetic results.

Mt Martha Bridge, Melbourne	University of Canberra student accommodation	Aldi, Belmont

For more information regarding this finish please refer to 10.6.11 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Case Studies:

The Kerrie Murphy Building, Ultimo, Sydney

University of Canberra, student accommodation

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Painting
Painting is the application of a coating (paint) that adheres to the surface of an element, creating an outer skin. The paint colour will be somewhat transparent unless a thick coating is applied to ensure the paint is opaque. The advantage of thicker opaque coats (and coatings such as texture coatings) is that it can mask small surface inperfections. Paint generally will last for 10+ years, but is susceptible to wear damage (scuffing). There is an infinite range of colours and colour matching is available.

Ikea Perth store	Metro Village Rosebery, NSW

For more information regarding this finish please refer to 10.6.11 of the Precast Concrete Handbook (click here to buy the Handbook) or talk to one of our Members.

Case studies:

Ikea Megastore, Innaloo, WA

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