Translucent finishes alongside opaque paints
Timber houses are a living cultural tradition in the Nordic countries. Surface treatments improve the durability and appearance of timber surfaces, and also help a building to blend into its environment. A new generation of translucent coatings now exist alongside traditional exterior paints. However, applying translucent finishes poses its own challenges.
Although many people want their wooden surfaces to retain a natural appearance, weathering should be taken into account when applying exterior finishes. When designing a wooden building, you should decide how you want the exterior walls to look after five or 30 years. If you don't want old-looking grey wood, then you will have to protect your timber.
Things are different for interior surfaces – wood slowly changes its colour and appearance as it ages. A decorative wooden surface is often protected using a transparent varnish, wax, or oil. It can also be left completely untreated.
Translucent or opaque – appearance and reapplication
In the Nordic countries, timber façades are usually made of coniferous species – spruce or pine – which are easy to treat in a variety of ways. Whether you choose a transparent or opaque finish is largely a matter of taste, or a question of the building's general style and appearance. People often want to use a translucent finish to retain the solid timber feel of a log house, while a clapboard detached house is often finished using long-lasting, opaque house paints. In addition to appearance, both finishes have technical properties that may favour one option or the other. A translucent finish is better for a smooth planed surface, as a film-free or thin-film surface is easier to take care of.
One criterion for choosing your surface finish is, of course, how often you'll need to reapply it. A translucent finish needs reapplying far more frequently than an opaque finish. A high-quality opaque finish on a sawn timber surface should last for over 20 years. Although translucent finishes do not last as long as opaque ones, there is great variation in how often they require maintenance.
A translucent finish on the shadowy side of a log house may not show any discolouring at all after 15 years, while the sunny southern side may require retreating after only a couple of years. One thing to note, however, is that a film-free or thin-film translucent finish is much easier to reapply than an opaque finish. A translucent finish does not flake – it simply fades or blanches in the sun. The only preparatory work required is washing or even just brushing the surface, followed by one coat of wood stain over the faded area.
Tinted ﬁnishes provide protection from sunlight
Any translucent finishes that are used outdoors should be tinted. The pigment (that is, the colour particles) stops the UV radiation that attempts to break down the wood's surface cells and the lignin that binds them together. The more colour particles there are, the slower the wood's surface ages. In other words, the stronger and more opaque a wood stain's colour is, the better the protection it offers from the sun. A completely colourless wood stain or varnish does not provide any kind of UV protection, and the treated surface will therefore grey as fast as an untreated surface. There are also differences in pigments – colour matters. For example, the yellow and red pigments contained in iron oxides withstand UV radiation much better than organic blues. A paint's binder also affects how long its colour will last – many people are all too familiar with how quickly an oilpainted blue house will fade.
The binder binds the pigment to the wood and provides protection from the elements
Typical binders used in translucent finishes for exterior use are drying oils, alkyds, or acrylics. The wood's cells absorb the binder and bind the pigment to the wood's surface. Depending on the coating's intended use, the binder will form a more- or less-dense film that protects the surface from exterior moisture. Wood is a hygroscopic material that will absorb moisture from the air. Continual fluctuations in moisture content cause wood to swell and shrink, and this leads to splitting. A surface treatment that forms a film over the wood reduces and balances out these fluctuations in moisture content, thereby lengthening the life of wooden structures. However, it is impossible – and not worth attempting – to completely prevent these fluctuations in moisture content. The moisture permeability of exterior surface finishes ”breathability” is regulated so that moisture can move as naturally and appropriately as possible.
Protection from decay
As an organic material, wood is a good growth medium for rot fungi, mildew and mould. Climate change, and in particular an increase in humidity, provides these organisms with better growing conditions. The right kind of surface treatment also provides chemical protection. Wood protection primers contain fungicides that are absorbed into the wood and protect it from harmful microbes. The purpose of primers is to be absorbed by the wood, thereby infusing the wood's surface with chemical protection. As wood protection primers do not form a film, they allow the next coat – the wood stain – to adhere to and be absorbed into the wood's surface as well. Wood stains also contain protective substances whose task is to protect the treated surface from mould. Like exterior paints, exterior wood stains provide good protection from surface mould growth, but are less effective when the surface gets dirty. This is why you should keep a house's façade as clean and dust-free as possible.
The industrial surface treatment of cladding
There are many benefits to be gained through the industrial surface treatment of construction timber: painting conditions are optimal, and the timber is dry and quality-assured. Industrial coating is also fast and precise, which increases the cost-effectiveness of timber construction. Teknos' solutions for the wood industry guarantee a durable, attractive and uniform undercoat, as well as a basecoat and/or intermediate coat that will facilitate and hasten on-site surface treatments. The majority of the façade timber used in contemporary Finnish new construction has already been industrially primed.
Teknos is the market leader in coatings for the wood industry in the Nordic countries and Central Europe. Teknos' extensive range of woodworking industry products includes opaque and translucent solutions for all timber structures from eaves, fences and decking to doors, walls and windows. The standardised and CE-marked TEKNOSAFE 2407 fire retardant coating system can now be used on an even broader range of timber façades.
On-site coatings and coating conditions
All undercoats, basecoats and surface finishes can, of course, still be applied on site. This is the case with, for example, log houses, which are treated on site with Teknos' range of WOODEX products. And the application of the final surface coat to industrially primed timber façades is still carried out, almost without exception, on site. This guarantees a flawless and nicely finished end result, and also ensures that there are no uncoated areas, for example, cut surfaces, on the cladding. Repainting is always carried out on site using products specifically designed for maintenance and upkeep.
Teknos' wood stains, trade paints, and house paints have been designed for brush application. Paint can, of course, be applied using a roller or sprayer, but the final coat should always be finished with a brush. Exterior products have been developed to function in the widest range of conditions possible – temperatures of between +5°C and +35°C and a relative humidity under 80%.
Translucent products for a range of uses
Modern wood stains are water-dilutable. On wooden surfaces, they work as well – and sometimes better – than earlier solvent-based coatings. The binder plays the crucial role in determining a coating's durability and effectiveness. All types of binders, from acrylics to oils and alkyds, have long been used in the manufacture of water-dilutable products. Their absorbability and weather resistance are as effective as those of solvent-dilutable products. Nowadays, coatings for the wood industry are almost without exception water-dilutable. Traditional solvent-dilutable versions are still available for use in the construction industry alongside water-dilutable products.