Unlike paints, Varnish can act as a magnifying glass on timber and either bleach it out or darken it (depending on the timber and humidity) either way it is expensive to fix so much so that in extreme cases (like cedar)it would be cheaper to re-clad. The main culprits here are the sun and the rain with Australia’s extreme climate bathing us in the highest UV doses on the planet!
You know what happens when we stay in the sun to long – yep that’s right we get sun-burnt, although we can protect ourselves by wearing sunscreen factor 30 to some extent, its best not to overdo it. The problem with varnish, danish oil and other clear finishes is that because they need to be transparent they have little in the way of UV blockers and solids to protect themselves and the wood they cover, especially in the sun.
Modern paint, on the other hand, is virtually all solids and UV blockers with premium brands utilising nanotechnology to tighten up the structure of the molecules increasing the time it takes for the paint to break down (most manufacturers guarantee 15 years).
When it comes to the Australian sun – all bets are off! If you want to clear coat exterior timber we recommend using a decking oil which will need to be reapplied every 6 to 8 months as it drys out (it removes itself so you don’t have to). Over the years the wood will darken as the oil residue builds up but this is considered an acceptable trade-off.
You may also wish to consider relatively new and very realistic artificial plastic or aluminium wood imitations strip products. Although these will cost slightly more upfront you will get your money back in spades through avoiding that expensive upkeep.
Tip; If you simply must have a clear finish try and get the product with the most solids possible while providing acceptable transparency. It is also possible to extend the life of clear finishes by carefully adding colorants or paint tints.