- Composite decking review (WPC).
- What is the best decking timber type?
- What is the best decking treatment?
Types of wood finishes
What is the best deck finish?
The reasons for applying timber finishes at all are:
Firstly, wood finishes are water-repellent and that allows to control the moisture content. By absorbing and releasing moisture, wood expands and shrinks. Severe changes of the moisture content can cause deformation, the boards can warp or even crack.
Secondly, pigment enriched timber coatings protect the timber from UV-light (ultraviolet light) to a certain degree. Is wood exposed to ultraviolet radiation (sun light) over a long period, a tenth of a millimetre of the surface will get damaged (in particular the lignin will become denatured). The cellulose gets pulverised and the colour of the surface turns into a silvery-white to dark gray. Not a big deal for the timber itself but a film building finish will lose its adhesion and peel off.
And thirdly, timber finishes are used to simply enhance the look and colour of wood.
It is important to consider the different characteristics of the finish types before applying them as it may be difficult to change from one type of wood finish to another one. For example a paint seals the surface and prevents a later coat of decking oil from penetrating into the wood.
- Decking oil (non water based) is easy to apply and requires the least preparation. It is water-repellent, penetrates a few millimetres into the wood fibre and supports the natural weather resistance of timber. In general non water based decking oils darken the colour similar to wet timber. Commercially sold decking oils contain usually colour pigments to enhance the appearance and protect from UV-light. The colours are often named by the type of wood with similar colour; a ‘Natural’ colour could be close to clear and the name ‘Jarrah’ would indicate a reddish brown colour. Non water based decking oils wear out quicker and often need recoating after 6 to 12 months.
- Decking oil (water based) usually blocks the wood pores and covers the surface with an acrylic film. Translucent colours change the natural colour least but in turn also protect less from UV-light. The wood should be free of dust and oil before applying the water based decking oil. If non water based decking oil was used before, the surface needs intensive cleaning and perhaps sanding otherwise there is a chance that the acrylic film won’t stick to the timber and thus peels off. Worn or damaged parts should be sanded and recoated as soon as possible to avoid colour changes. Water based decking oils require more intensive preparation of the timber than non water based ones but should outlast at least 12 months.
- Exterior wood stain is (so called) semi translucent and designed to enrich the natural colour of the wood. They are easy to apply and usually last longer than decking oils. They penetrate deep in the timber and therefore do not peel off like film building products sometimes do. Wood stains are also often used as a primer to just stain the timber and then coating it with a film building product. The high content of colour pigments is also beneficial for excellent UV-light protection. Generally wood stains can require more care in surface preparation than for decking oils but can last at least between one and two years.
- High performing coatings and paints (also top coats) seal the wood pores, cover the surface with an acrylic film, and do not penetrate into the timber like oils and stains. They virtually isolate the timber from any moisture and can develop a shiny surface. Often a wood stain is applied as a primer before these finishes if an intensified colour is desired. Paints have the same thick consistency but are even richer in colour and thus cover the natural wood texture completely. A big advantage is the excellent protection from ultraviolet radiation. However, film building finishes are generally more sensitive to abrasion. Areas with frequent traffic can get damaged and the colour of the wood can turn grey, especially if there is sometimes sand or dirt on the timber deck. Each time these finishes are applied, they require comparatively high preparation of the timber surface but the service-life can be two to three years, sometimes longer.