How to tell timber has been sanded enough before refinishing with polyurethane?

Question

Hello. Thanks for having me. 🙂

I purchased a Practa Acacia Timber Benchtop 2200 x 600 x 26mm a year or so ago which I've been using as an underdesk sliding tray to hold my keyboard (musical instrument). I've been wanting to have a go at refinishing the timber as a project and to hopefully match my acacia desk a little better.

I've sanded the timber with 80 grit sandpaper a fair bit and it's much lighter and duller in appearance now. I was wondering if, based on the photos, I've sanded enough of the oil away to begin smoothing, cleaning, and then refinishing? Or if there's a way to test if the timber is deoiled enough? (The benchtop was listed as 'unfinished timber' so I'm not sure if the darker colour of the acacia was just from the natural oils or if that's a listing mistake).

Before sanding:

After sanding:

Any advice would be greatly appreciated.

-Bree

JacobZ · Answer

No worries @BreeH.

Don't hesitate to reach out if you need any advice along the way.

Also, it would be great to see some pics if you remember once it is done.

Jacob

BreeH · Answer

I will try out the water method and check out that guide. Thanks Jacob. 😊

JacobZ · Answer

Hi @BreeH,

Welcome to the Bunnings Workshop community, it is fantastic to have you with us.

Acacia is naturally quite oily, and these timber panels will have a light oily coating on the surface. The listing notes the finish as "timber", which is technically correct, but there is definitely oil present. I will reach out to the website team with your feedback.

A simple way to check whether you've removed the previous oils is to place a very small amount of water on an inconspicuous area of the timber. If the water readily soaks into the timber rather than sitting on the surface or beading up, that's a good indication you've sanded enough and are back to bare timber.

From experience and what I can see, you've done plenty of sanding already to remove the surface oils and you are ready to move forward with a higher grit sandpaper. Even if there is a small amount of oil left, the higher grit sandpapers will still help to remove it.

Once you've finished with the higher grits, make sure you brush/vacuum/wipe the surface down well to remove any remaining sanding dust as it can affect your coating.