The stain contains oils which penetrate the timber surface. This protects the surfaces rather than allowing it to deteriorate. Paint is a protective surface on the surface of the timber.

Un-oiled they will deteriorate slowly rather than rotting. Rotting is caused by being damp for extended periods (regularly for months, years, etc.).

Some timbers are better than others for outdoors. Treated pine (H4) will last for years in the ground. Untreated un-oiled pine not long at all.

There are many old farm sheds that are clad in untreated & un-oiled timbers and they're still surviving. I've seen many old decks that need decking boards replacing due to being left un-maintained. A deck area has little protection from the elements so needs continuace maintenance.

For this deck we used thick hardwood. A mountain Ash variety. The boards are 32mm thick and have a slight concave on the bottom allowing them to breath against the joists, a speacialty from Radial Timber in Victoria Aust.. As mentioned above provided the timber has adequate air circulation it will last for years. The council use similar boards for beach and forest board walks. The only maintenance that may need to be done is that occasionally you get some cupping or mild splitting on the surface in the odd board. This can be easily sanded. This deck is now 8 years old and has needed no maintenance :)

If you use a hardwood then they won't rot; and all timbers used for decking should be plantation grown and from a local source. But of course they are much dearer than other cheaper forms. A sustainable alternative is to use recycled plastics as decking material which also doesn't require treatment.

My understanding is that woods that naturally have a high oil content will weather well, the common belief is that adding oil will help the wood last longer. However, its not necessarily true, I think ultimately its more about the look and what people like. I personally think that using many timber decking oils that are not natural actually require more maintenance in the long term, than just leaving the wood to age naturally. Adding a petrochemical derived oil, thinned with toxic solvents, to beautiful naturally hardy timber is a good idea in my opinion.

Cedar shingles are a great exampled of wood that does not need to be sealed or oiled. They will last on a roof top for many many years.

I found this fence in Sydney which I love - have talked to the owner and found it is western red cedar treated only with lanolin oil.

They haven't recoated it in two years,

Spotted in Sydney. Must be hardwood. But looks untreated? And screwed in with bo · More Info