How to oil timber that has weathered unevenly?

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When a timber finish is uneven, you are unlikely to get a great result when re-oiling unless you sand the timber back first. While sanding can be a reasonable amount of work, the timber will look like new again afterwards.

Here is an example of an unevenly worn Merbau deck sanded to bring it back to new condition - Deck renewal using floor sander.  

There is a comprehensive guide on How to sand a deck from the Bunnings team, which includes a video and a full list of tools and materials. You can see how they achieve a uniform colouring with fresh timber before proceeding.

Note that some products say they can be applied over existing coatings. You might get reasonable results, but if any part of that old coating fails it will take the new coating with it. 

If you're not keen on sanding, you can try a product like Intergrain UltraPrep Timber Cleaner or Cabot's New Timber Prep to strip as much as the previous coating off as possible. - EricL