How to remove black watermarks on Acacia benchtop?

Annaki74

Hi, I just bought an acasia wood benchtop for my kitchen remodel, I have oiled it twice with Monocel benchtop oil with 24 hours between coats, waited at least 48 hours before using it, but as soon as it got moisture on it watermark appeared. I've been using same benchtops for the last 5-6 years, both in my kitchen and bathroom, used same oil to seal (and never even recoated) and never had those marks, a fair bit of wear yes, but no marks. So why now and how do I fix it? Do I need to sand back the whole thing now?

EricL

Hello @Annaki74

Welcome to the Bunnings Workshop community. It's sensational to have you join us, and thanks for sharing your question about your benchtop.

That is a bit of a mystery, I'm surprised that the water passed through the Monocel coating as you've put two coatings on. The only reason I can think of is that the Monocel did not get absorbed properly by the timber top surface or is till curing. Did you by any chance sand the surface first before applying the Monocel coating? There may have been oil and grease contaminants on the surface or perhaps a protective coating. It would have been necessary to sand the surface so that it is smooth and flat and ready to take on the Monocel sealer.

I propose trying out a standard repair step. The black marks are most likely tannin stains that's reacted with the water rather than trapped moisture. Acacia is naturally rich in tannins, and if water is left sitting on the surface, especially during the first few weeks while the oil is still curing and building protection, the tannins can react and produce dark grey or black marks within the timber.

I suggest lightly sanding the affected area with 320–400 grit until the stain is removed, feather the edges into the surrounding timber, then apply two or three thin coats of Monocel Benchtop Oil, allowing each coat to dry as directed.

If this benchtop is being used around a sink or in a high-moisture kitchen, it's also worth considering whether an oil finish provides enough protection for your needs. While Monocel gives a beautiful natural appearance and is food-safe, it doesn't form a waterproof film. A polyurethane benchtop finish, such as Cabot's Benchtop Timber Finish, offers significantly better resistance to standing water and everyday kitchen use. Just a quick reminder that the benchtop would need to be sanded back to timber before applying the Cabot's benchtop finish.

Here is a handy step-by-step guide: How To Install And Seal A Timber Benchtop

Please remember to wear personal protection such as gloves, goggles and a mask.

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

Eric