How to remove bleach mark on deck?

[JoanD78]

Our deck needs the usual sand and oil - but roof washing left a large bleach mark across the middle of it - any ideas from anyone???

[MitchellMc]

Welcome to the Bunnings Workshop community @JoanD78. It's sensational to have you join us, and many thanks for your question about deck oiling.

Could you please upload a couple of photos of the deck so that members can get a better idea of the issue? If you need a hand with uploading images, I can walk you through the steps.

In terms of what’s happened, the bleach has effectively lightened the timber, so you’re dealing with a bleached patch. If the mark isn’t too severe, you could try giving the whole deck a clean with a deck cleaning solution and then apply a tinted decking oil – often this is enough to even out slight colour discrepancies. It would be worth doing a test section to see if this works. If the bleaching is quite strong and a tinted oil won’t disguise it, the only real fix is to sand the deck back until you reach fresh, unbleached timber before re-oiling.

Please let me know if you have any questions.

Mitchell
 

[Jacob-Hawkins]

Hi Joan - very sorry the roof wash (Likely Sodium Hypochlorite) has ended up on your decking - here's what you can do about it now:

Neutralise ASAP: Flood the area with water, then apply an oxalic-acid deck brightener over the entire deck (follow label). Keep it wet 10–15 min, light scrub, then rinse thoroughly. Let it dry 24–48 hrs.

Sand uniformly: Don’t spot-sand the stripe. Sand full boards end-to-end so colour blends.

Main area: 60–80 grit; edges/handrails: 80–100 grit.

Vacuum/dust off; avoid pressure washing (it furs the grain).

Re-oil: Use a penetrating decking oil. Start with a tint close to your original.

If the line still ghosts through, add more pigment (darker tint masks better, but also hides grain). Do two thin coats with proper dry time.

Always test a small patch first.

Notes

Depth of sanding depends on how deep the bleach bite is vs how perfect you want the finish.

Protect plants and surrounding surfaces during the acid step; wear gloves/eye protection.

Bottom line: Oxalic brighten → uniform sand → re-oil, adjusting pigment as needed to blend.

-Cheers, Jacob