Decks and exterior timber features are an important part of many Australian homes, and finishing and maintaining them has been the subject of many decades of research due to our high levels of sun and rain.
The key requirement of an exterior wood finish is to repel water. If timber absorbs water it will ultimately warp, crack and rot. Water repellency can be achieved by a finish that create a film over the timber. However the constant expansion and contraction exterior timber is subject to from the sun heating it up, means most film forming finishes will ultimately crack or peel. When this happens water gets in and the finish requires renewing. However renewing a film forming finish requires stripping or sanding off the old deteriorated finish. This is usually a very big job, so most manufacturers have now moved to producing penetrating finishes which repel water but don't ever crack or peel. The tradeoff with these is that they require a top up coat regularly, as they dry out over time. However this is generally fairly easy to do because it doesn't require stripping or sanding.
If we also want exterior timber to maintain its colour then the finish requires something to stop the greying effect of the suns rays. This is why most exterior timber finishes contain tints. These are special micronised tints that block the suns UV rays from greying the timber. These tints can range from light honey colours through strong colours. Usually the stronger the tint the more protective and long lasting the finish will be. However some exterior timber finishes don't contain any tints and are designed to repel water but allow the natural greying of the timber.
Horizontal timber surfaces, such as decks in full sun, are the most exposed to the drying out effects of sun and rain. These will require the most maintenance - usually an annual top up coat. Vertical surfaces, or timber that is semi protected, will generally last longer before requiring a top up coat. The key factor in deciding if it needs a top up coat, is wether it still repels water. If it no longer repels water, then it needs a top up coat.
Below are our top five picks for penetrating exterior timber finishes that have eco credentials, durability, give aesthetic results, and are easy to apply and maintain. Each are good products and suit different aesthetic tastes, requirements, and price ranges.