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I’ve just finished building my deck with pre-oiled Merbau decking timber from Bunnings. I noticed that the surface goes splotchy when water falls on it. Do I need to seal/waterproof it? If so, what do I use? Is the Cabot’s Aquadeck the right stuff to use? Do I need to wait 4-6 weeks for the wood to weather first or can I seal it now?
Welcome to the Bunnings Workshop community @jo_mw. It's a pleasure to have you join us, and many thanks for your question about waterproofing your deck.
You are on the right track, and that splotchy look you are seeing is completely normal for fresh Merbau. Pre-oiled boards still contain a lot of natural tannins, and when water hits the surface those tannins move around and create patchiness. It is nothing to worry about, and it settles once the timber has weathered properly.
You have two options from here. You can let the deck weather naturally for at least four to six weeks, which allows the tannins to leach out on their own. If you want to speed things up, you can hose the deck down every few days. A thorough rinse helps flush the tannins out quicker, so you may only need a couple of weeks of this before it is ready for oiling.
Alternatively, if you prefer to prepare and oil it sooner, you can scrub the deck now with Cabot’s New Timber Prep. It is designed specifically to remove the surface tannins from new hardwoods like Merbau. Once you have scrubbed and washed the deck, allow it to dry completely, then you can go ahead and oil it.
Cabot’s Aquadeck is an excellent choice. It is a water-based decking oil, easy to use, quick drying and gives a great finish on Merbau. Just make sure the timber is clean, dry and free of tannin bleed before applying it.
Please let me know if you have any questions.
Mitchell
