Exterior timber and deck features are a valued part of many Australian homes and commercial buildings. Finishing them and keeping them looking good in our harsh Australian sun and rain is an ongoing job! Many decades or research has gone into creating products that will achieve this whilst keeping the labour to a minimum.
The key requirement of an exterior wood finish is to repel water. If timber absorbs water it will swell and ultimately warp, crack and rot. Water repellency can be achieved by a finish that creates a film over the timber. However when the sun heats timber it will expand and contract considerably, and this means most film forming finishes will ultimately crack or peel, because the film becomes hard and rigid over time and wont expand and contract with the timber. Water gets in through the cracks and the finish starts breaking down. Renewing a film forming finish then requires stripping or sanding first to remove this deteriorated finish. This is usually a very big job, so most manufacturers of exterior timber finishes have now moved to producing penetrating finishes which expand and contract with the timber instead of rigid film forming finishes.
Penetrating finishes repel water and don't crack or peel. However they dont last as long as film forming finishes. They require a top up coat regularly because they dry out over time. This is generally fairly easy to do. Simply clean the surface and apply another coat. Poor quality finishes may only last 6 months before requiring a top up coat. Good quality finishes will last 12 months or more depending on the exposure. For example decks in full exposure are constantly subjected to full sun and rain so likely need a top up coat annually. Vertical timber features or timber that has a roof over it will likely last 4 or 5 years before requiring a top up coat. When it stops repelling water it needs a top up coat.
If we want exterior timber to maintain its colour then the finish also 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 these tints can also build up over time and detract from the natural look and feel of the timber. A good tip to avoid this is to make sure you clean the timber down with a good timber cleaner before applying a maintenance coat. Thus removing any surface build up of tints.
Some exterior timber finishes such as Lanotec Timber Seal don't contain any tints and are designed to repel water but allow the natural greying of the timber.
Below are our top five picks for penetrating exterior timber finishes that are eco friendly, durable, aesthetically pleasing and easy to apply and maintain. Each are good products, have different aesthetics, different purposes, and different price ranges.