Selecting suitable coatings for Australian timbers takes a bit of homework, but can lead to Grade A finishes. By Finn Seccombe.
Having worked in boat building and joinery for many years I have experienced both the pain and joy that choices in timber coatings can bring. With time and money at stake, builders and architects need peace of mind that the finish they have specified is not going to come back to haunt them.
When it comes to timber preservation, the Australian outdoor environment is one of the harshest in the world. We have large temperature and moisture variations, blistering UV levels (particularly in Victoria and Tasmania) and a diverse range of timber species and products, each with their own unique challenges.
Paint formulas and systems are becoming ever more complex as manufacturers strive to meet the demands of the Australian environment, changing government regulations, and the ever-evolving requirements of architects, builders and their clients. In an increasingly competitive market, products are expected to be industry friendly, long-lasting and safe for both the consumer and the environment.
Toxic solvents and drying agents such as mineral turps, Terebine, lead and cadmium were very effective at protecting timber in times gone by, but are now being phased out due to their harmful effects on humans and other organisms. This has led to a new wave of innovation in water-based finishes and natural oil-wax coatings for both indoor and outdoor timber surfaces.
For those of us who don’t have a degree in chemistry we frequently find ourselves having to put our trust in paint reps and what is written on product webpages. Every manufacturer assures us that their product is the ‘bee’s knees’ and more often than not, the accompanying Material Safety Data Sheet (MSDS) seems to have just enough technical information to be confusing but not enough to extract the answers we’re in need of. To make the best decision on behalf of your client you might have to do a bit of leg work.
The first principle is: trust your own experience. There are plenty of tried and tested products on the market and if the finish you have been specifying for fifteen years has never failed then why switch?
The next principle is: talk to other builders, architects and paint specialists. Each one of these professionals contains a wealth of information on which products are cost effective, industry ready and have the longest lifespan. Their reputations and livelihoods depend on it.
Finally, and importantly, before specifying a coating, listen to what the product manufacturers tell us. Not all painting situations are going to represent the ideal factory conditions recommended by the manufacturer so you need to fully understand product parameters such as temperature and air moisture.
Putting these principles into action, here are some of the big issues facing the building industry (particularly with exterior timber) and some pearls of wisdom I have gleaned from the paint professionals.
UV: the paint killer
You may have noticed that the north-facing side of buildings always suffer the most when it comes to surface deterioration. This is due to the destructive effects of the sun’s UV rays. These effects are often compounded by prevailing wind and rain patterns, further accelerating decay.
UV light is invisible, but it is very powerful. When it strikes a painted or oiled surface it can break down molecular bonds, causing the coating to go brittle, crack or peel off. The aim for exterior coatings is to block out as much UV as possible. There are three main categories for exterior timber coating that help to address this issue:
Opaque paints mostly have an acrylic binder with oxides and fillers to provide colour and depth of film. Oxides (e.g. titanium oxide) and colour pigments also act as a barrier to UV penetration, slowing the destructive effects of the sun. Dulux Weathershield and Haymes Solashield are leaders in Australian exterior paint with guarantees of up to 20 years. These products are suitable for air or airless spray application on larger industrial projects
Transparent films, such as Sikkens Cetol (oil based or water based), and Intergrain UltraDeck (water-based, but proven to significantly outlast traditional finishes), are semi-transparent finishes through which you can still see the grain of the timber. They usually contain pigments or stains that act like sunscreen, reducing the damaging effects of UV light. Sikkens Cetol HLSe has been popular for many years among architects and builders wishing to specify a product that preserves timber decking and cladding while maintaining the natural look of timber. You can expect two to five years life between re-coats in fully exposed positions like decks and railings and about 10 years in more shaded positions. This will also depend on the type of timber used. Timber with more open grain such as Tallowood and Blackbutt will have a tendency to form small cracks from moisture-related movement whereas tighter grain hardwoods such as Merbau and Jarrah are more stable. Teknos offers a range of industrial primers and coatings that can be applied to exterior timber and joinery via dipping, flow-coating or spraying technology. These are designed for application in a factory setting, where conditions, such as temperature and moisture can be controlled – optimal for consistency and longevity.
Penetrating oils soak into the timber surface and dry, forming a matrix with the natural fibres that repels water. This stops surface checking (cracks) and keeps the timber dimensionally stable. They often have waxes and oxides added that sit on the surface as a thin film adding U.V. protection and enhancing the natural lustre of the wood grain. Cutek and Cabot’s are two Australian companies that manufacture external penetrating oil that can be applied clear, allowing the timber to naturally ‘grey off’, or with a tint if you’re after a more permanent stained look. The growing demand for naturally finished timber in architectural facades calls for products that will protect the surface without creating a ‘plastic’ look.
Specialist paint types
Volatile organic compounds (VOCs) are organic (carbon-based) chemicals that have a low boiling point, causing large volumes of molecules to become airborne at room temperature, a trait known as volatility. These vapours can cause WHS problems for industry and health issues for residents and workers who go on to live in or use the ‘off-gassing’ spaces.
While Low VOC paints used to be the preserve of specialty ‘eco’ manufacturers, all the main brands now stock options, especially European-manufactured ranges such as Teknos. These have modified formulas to maintain some of the desirable features of High VOC paints, such as easily maintaining a wet edge, but some are still perceived as more difficult to apply than ‘traditional’ paints. This is usually due to application. Synthetic roller sleeves deliver smooth, well-blended finishes and can also be used for back-rollering after a spray application.
If you do choose to apply a product with high VOCs, safety precautions such as adequate ventilation and wearing carbon filter respirators should be taken seriously. Thankfully, the most dangerous VOCs such as Terebine, ammonia, cyanoacrylate, acetone, benzene, cyclohexene and toluene have been removed or reduced in modern paint formulas.
Graffiti removal and the subsequent repainting of damaged surfaces is an expensive exercise. Dulux has developed their Precision Anti-graffiti coating to deal specifically with this problem. Dulux Precision Anti-graffiti coating is a heavy-duty coating, providing long-term surface protection against graffiti in private and public spaces. It is specifically formulated to be applied to a variety of bare and painted surfaces including timber. Aerosol and other paints can be removed easily with high pressure water.
Mould and bacteria
Painted areas that are continually exposed to high moisture and humidity are often afflicted with mould and mildew. Mould can occur on painted surfaces but can be a bigger issue if it develops in the structure of the timber. For susceptible timbers or in mould-prone environments, the combination of a mould-preventative product and a mould-resistant paint provides the best protection.
Most paint manufacturers have mould-resistant products in their range. Some professional standouts include Intergrain TSS Mould Preventer, which is ideal for on-site applications and for industrial use, and Teknos Aqua-Primer 2907, which offers excellent protection against mould and blue stain.
In the domestic sector, Resene Cleancote is a dirt-resistant waterborne paint known for its durability and excellent mould resistance. It is formulated for hot, humid climates and exterior areas that are often wet. For interiors, Haymes Expressions range has very effective anti mould and mildew properties, stain and mark resistance and one of the lowest VOC levels on the market.
For buildings where optimal hygiene is required such as hospitals, rest homes, medical centres and clinics, anti-microbial agents such as silver-ion-coated titanium oxide are added to paints, killing pathogens that come into contact with the surface. Resene ClinicalCote is a low odour, washable waterborne paint finish that is leading anti-microbial coating technology. It is designed to withstand alcohol and glycol contained in hospital cleaners, ensuring a long maintenance-free lifespan.
Fire-retardant coatings for timber
In the TTN December 2017 issue, we covered some of the key points about how timber performs when exposed to bushfire. Emerging recently are a few products that raise the Bushfire Attack Level (BAL) rating of timber and lower the risk that exposed timber will catch fire. A good example is the fire-resisting coating Fireshell F1E from Australian company, Exfire, which is designed to protect vulnerable exterior timber (such as pine cladding or decking) from fire threat up to BAL 29. Fireshell complies with the bushfire-resisting timber requirements of Australian Standards AS3959. It can be brushed, rolled or sprayed.
As timber cladding, window, door and cabinet manufacturers move towards automated and robotised finishing systems, paint manufacturers have been developing coatings that are compatible with factory systems. It makes sense that finishes are applied in a controlled environment rather than the messy world of unpredictable weather and building sites. Specifying pre-finished timber products may seem expensive at the outset, but when they are being installed in high or difficult access areas they can be incredibly cost effective. No scaffolding or wet paint onsite required! Companies supplying these products such as Intergrain, Teknos and ADLER have incredibly high-quality standards in order to achieve finishes which are consistent in appearance and performance. As demanded by industry, they are also low in VOCs, cost effective, compatible with various robotic application methods and robust enough to cope with Australian conditions.
Use the tools
Recognising that residential building and renovation are going to remain huge sectors, most painting-related companies now offer scaled-down versions of industrial solutions for application and clean-up that can be used on suburban sites. Australian company Haymes has come up with a neat solution for water-borne paint disposal, the Ecocare Wash Treatment System. Painting equipment (brushes, rollers, paint trays) are conveniently cleaned in the unit; paint solutions are converted into clean water, leaving solids that can be disposed through general waste. This prevents harmful solids/pigments from ending up in waterways and makes clean-up times significantly quicker. It is used in conjunction with Haymes Ecocare Treatment powder, which binds to paint solids, allowing them to separate from the water.
In a similar vein, Wagner Australia offers the Control Pro range of compact airless sprayers. Small enough to fit in a car boot, they are light in the hand and have reduced overspray, making them ideal for interiors or jobs that have limited access.
When it comes to paint, ultimately, the same rules apply whether you are specifying finishing products for multi-rise or for residential buildings. Make sure the product is tried and tested. Make sure the product is compatible with the specified timber and, make sure that it is suitable for the particular environment in which you are building or planning to build.
Image: Dulux Weathershield in Teahouse (light grey) and Domino (dark grey).