As the industry increasingly focuses on ways to move construction into the factory, pre-finishing timber cladding before it is installed on site could be the next big step for the material.
Timber finishes for exterior cladding applications are often seen as a necessary step for most projects in improving a building’s durability and in some cases, enhancing its aesthetics. According to Wood Solutions, unfinished, unprotected timber will inevitably weather as a result of gradual changes to its “physico-chemical structure brought about by temperature and moisture content variations”.
Although this rate is generally slow, at about 6mm per century, some timber species are more susceptible to dimensional change due to moisture content, absorbency and density, as well as environmental conditions. Finishing systems must therefore be able to cater for these movements.
There is a myriad of finish types available on the market, ranging from conventional opaque systems and natural timber finishes, to glossy coats, solid stains and water repellent preservatives – all governed by AS/NZS 2311 – Guide to the Painting of Buildings. What types of finishes to choose from, however, depends on the type of look a specifier and client are after, as well as what maintenance expectations clients have.
“Acrylic paint needs the least maintenance, with some manufacturers now offering guarantees of ten years or more. Pigmented stain is next best for lasting properties, while clear finishes need the most frequent attention,” Stephen Mitchell, from Wood Solutions and the Timber Development Association, explains.
“Some new water based finishes have excellent durability as well as easier reapplication. If the timber cladding is shielded from the weather by verandas, wide overhangs, maintenance is dramatically reduced.”
However Mitchell adds that pre-finishing timber cladding – a growing trend for the industry – can deliver a better product less prone to movement problems while a building is under construction.
Final finishes are easier to apply correctly in a factory before delivery, which minimises call-backs. It also has the potential to speed up the construction process by reducing on-site labour and supervision requirements, as well as trade coordination delays.
Boral Timber Cladding used at the Monarto Zoo
Boral Timber, for instance, has seen an increased interest in off-site oiling of timber cladding products to reduce on-site labour costs and create an immediate aesthetic impact, and now offers the option to pre-oil the timber boards of its cladding range, which includes the Blackbutt, Spotted Gum, Tallowwood and White Mahogany species.
Woodform Architectural also pre-oils its Expression Cladding range, which eliminates the process of oiling each board all round on-site prior to installation. This is expected to provide the timber with some protection during construction, and gives the penetrating oil a chance to soak in prior to timber handling.
Spotted Gum Expression Timber Cladding by Woodform used for Quiksilver, Byron Bay.
According to Woodform, the deeply penetrating Cutek CD50 oil works from the front and back of the board to improve its dimensional stability. But, as with other products, a decision must be made at the design stage whether the colour of the timber will be maintained with an oil based timber preservative applied at regular intervals, or if it will be allowed to weather naturally.
The former will require a post installation second top coat with ColorTone stain to act as a UV-block, and a third and final coat after three weeks to further build the UV block and provide maximum timber hydration.
Spotted Gum Expression Timber Cladding use for Mereweather Surf House by Crone Partners. Image: Steve Beck. Source: Woodform Architectural
“It is important to consider the client’s long term expectations and recommend a suitable maintenance program, particularly for outdoor applications. Timber cladding can be refinished over time or allowed to naturally age to silver and grey tones,” advises Boral Timber’s national market developer manager, Clinton Skeoch.
Prefinished composite timber cladding systems have also become readily available, such as Innowood’s InnoClad system, which traditionally comes uncoated for internal applications, but can be pre-coated upon request to protect the boards from UV exposure. Colours from InnoCoat, the company’s quick drying coat, may vary 15 to 20 per cent after the first few months, with a two coat application having a life expectancy of three to five years.
InnoClad Architectural Composite Wood Cladding System
Other design trends & innovations
Apart from pre-finishing timber cladding before they are delivered on-site and installed, other trends for the material include deeper and more varied shadow lines, which add texture for cladded exteriors.
According to Skeoch, this can be achieved by using newer, deeper profile timber boards to create a groove that accentuates the natural features and contours of a building’s design.
The use of secret fixing in cladding projects is also growing. Rather than face nailing timber boards, builders and contractors are selecting newer profiles that can be fixed underneath boards to create a cleaner finish, and minimise visual distractions from the timber.
Woodform’s Expression Cladding is one range that comprises precision machined tongue and groove profiles, which allow concealed screw fixing and proprietary cornerstops.
Radial Timber’s radially sawn secret fixed Shiplap is another product that combines secret fixing with a third trend – the increasingly popular vertical shiplap installation. Its shiplap cladding is profiled from back sawn bevelled edge boards that interlock to produce a continuous vertical (or horizontal) cladding system.
Radial Shiplao 90 silvertop. Image: Radial Timber