How do you stain a weathered deck?

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In order for any stain or oil to be effective you'll need to sand the surface of your timber deck. The grey parts of your deck are old and will not absorb the stain or oil effectively. This will result in a patchy, unattractive finish if you do not sand it first.

The first task is to nail down the nails in your deck if any of them are sticking out using a nail punch such as found in the Kincrome 5 Piece Nail Punch Set.

The state of your deck's timber is also important to assess. If they are weathered, the edges can start to split. Any boards that are damaged with sharp edges or splinters should be replaced before commencing sanding. The guide How to renovate a timber deck has helpful advice for assessing and repairing damage. 

You can then proceed to sand the surface of the timber. The Orbital Sander available for hire at Bunnings has a sturdy head which is ideal for decking. You might also need a small hand-held sander for the perimeter of the deck if you have railings in the way. 

You can start sanding with something like 40-grit sandpaper but should finish with a finer paper such as 80-grit for a smoother finish. 

Sweep and wipe the surface clean after sanding, before proceeding to use your choice of oil or stain.

Here are some handy step-by-step guides from the Bunnings team:

• How to maintain a deck
   
• How to sand a deck 
   
• How to stain a deck

I also suggest having a look at these projects by Bunnings Workshop community members:

• Starting again with the deck - sand and strip by @Baz 

• Deck renewal using floor sander by @Jason 

• Deck strip, sand and oil by @DIY_Dan. 

In regards on what oil and stain to use, I suggest visiting your local store so that you can see on the stain sample boards what the product looks like once it is applied to timber. 

I recommend Intergrain 4L Merbau UltraDeck Timber Decking Oil. This water-based oil penetrates into the timber, while also forming a protective layer on top, for a durable and long-lasting finish. - EricL