Moldy teak is a tale as old as teak decking on boats. However, mold is more likely a result of circumstance. For mold to thrive, it needs shade, moisture, heat, and dust/dirt — think long, dusty shipyard periods, minimal sunlight, hot conditions, unevenly cambered decks, and poor deck drainage. Mold is pervasive, which is why it can become a big job. Air handlers and ducting, void spaces, and hatches all need to be inspected to stop its spread.
Ensure what you’re dealing with is mold. Aging, silvery-looking teak, simple water stains (from hard dock water), and dirt and grime can often be mistaken for mold growth and are much easier to remedy.
We’ll divide our approach into two parts: prevention and removal. Prevention is simply looking after your teak, and addressing mold’s potential to develop (shade, moisture, heat and dust). Some basics include regular cleaning, which doesn’t involve harsh chemicals. Once a week, a light deck wash with a pH-neutral soap is more than enough. Avoid leaving items on deck, and regularly move and clean underneath stationary items (pot plants, furniture pieces, etc.). Blade off standing water on the teak rather than letting it dry. Store cushions inside when possible and clean cushions regularly as mold thrives on outdoor cushions. More expensive options may be to sand and re-level the deck to ensure proper drainage, and to use a teak sealer such as Semco, which is great for sportfishers and one- or two-deck yachts, but bigger than that is likely impractical.
For removal, start with the least offensive and harsh option, then work down. A lot of deck work is preservation, so don’t start with the crowbar. Start with soap and a doodlebug, repeated a handful of times over a few days. If there’s no obvious reduction, move to distilled white vinegar, a 50/50 ratio with water. Apply to affected areas, let sit for a few minutes, then doodlebug and thoroughly rinse.
Then it’s time to try the oxalic acid solution. Technically an acid, it’s naturally occurring and is easy on teak. Again, let sit, scrub, and rinse. The next level is a commercial teak/mold cleaner. As for the final last resort — and it should only be a last resort — use bleach. At a 1:4 ratio with water, test on an inconspicuous area first, then apply and let sit for 10 to 15 minutes, scrub, and rinse. This will not only likely discolor your teak, but it will also break down the wood fibers and severely reduce its lifespan. I wouldn’t recommend it unless your teak is on its last legs and is getting replaced.
An intriguing development is the rising popularity of synthetic teak, which I’ve seen to be almost immune to mold, so our days of fighting moldy teak may be numbered.
This article was originally published in the August 2023 issue of Dockwalk.