How to remove tannin stains on the newly installed Merbau decking?

[BB_Hawk]

Hi

I just installed a Merbau decking but used the tarpaulin to cover it for a couple of weeks. There was rain during this period. When I remove the tarpaulin, there are noticeable stains on the surface of the decking, I know these are bleeding tannins mixed with water, but please advise whether I can still follow the weathering process to let it go, or I have to use the chemical product to wash them out?

The wet deckingThe wet deckingThe dry deckingThe dry deckingl 

Thanks

Hawk

[EricL]

Hello @BB_Hawk 

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about the tannin stains on your Merbau decking.

Yes, the stains you see on your new Merbau decking are indeed tannin bleed marks caused by rainwater mixing with the natural tannins in the timber, especially since it was covered by a tarpaulin, which may have trapped moisture. You can still proceed with the weathering process to let the tannins naturally leach out over time. This typically takes 8–10 weeks of exposure to weather (sun and rain). Ensure the deck is uncovered during this period to allow it to weather evenly.

However, if you prefer to remove the stains immediately or if the marks persist after the weathering process, you can use a product like Cabot’s Deck Clean. This is a deck cleaning solution designed to clean timber, remove tannin stains, and prepare the surface for oiling or staining. Simply follow the instructions on the product, scrubbing the deck lightly with a stiff brush and rinsing it thoroughly with water.

If you choose to weather the deck naturally first, keep an eye on it, and once the tannins have finished leaching and the surface looks uniform, you can move forward with oiling or staining to protect the timber.

Here is a handy step-by-step guide: How To Clean A Deck.

If you have any other questions we can help with, please let us know.

Eric

[BB_Hawk]

Thanks, Eric. I will wait and see the impact of the weathering. Will the product of New Timber Prep still work to remove those stains?

[MitchellMc]

Hi @BB_Hawk,

Yes, it will. But because these stains are caused by water and tannins pooling in an area, you might need to apply a couple of applications of the timber prep product to remove them entirely.

Mitchell