The cardinal rule is: NEVER scrub your teak deck
Scrubbing – from the first time – damages the soft areas of the wood grain creating peaks and troughs which will break when walked over. First effect: the teak wears down much faster. Second effect: the groves in the soft areas of the surface promote the growth of algae, fungus and mold. The fast answer is to give the deck a good scrub again and so the vicious circle starts again.
Is there a better solution? Yes, never scrub and treat your teak deck with Boracol twice a year. There are many authors such as the great Tom Cunliffe and shipwright Robin Benjamin recommending the same treatment for a silvery shining teak deck and longevity.
Boracol is a biocide based on quarternary ammonium and inorganic borate solved in water and glycol, hence not too bad for the environment (I think) and it targets algae, fungus and mold which are mainly responsible for teak decks losing their silvery shine and getting greeny and black.
So, I have ordered a 5l container of Boracol 5RH which is recommended for the leisure and amateur user. I will apply it towards the end of the season and report on the results in the future.
Update September 2017:
So far during our first summer season, our teak deck has never seen anything else than salt water, rainwater and a soft jet of fresh water every now and then. Bird droppings were simply rinsed off, and on one or two occasions gently washed off using a yellow sponge. We applied the first coat of Boracol to POLARIS’ teak deck.
Update March 2018:
It‘s now March 2018, the boat has been in the water all winter and the deck has maintained a smooth silvery shine. Still nothing but rainwater, saltwater and a soft jet of freshwater with the occasional yellow sponge for sticky gunk. There are no traces of black or green algae even after a quite wet and cold winter. We applied a second coat of Boracol and we‘ll see how this goes through the summer. So far we are very satisfied with the result.
Update January 2019:
We stuck to the rule: no brute force, just water of any form and a yellow sponge for obstinate dirt. Results are perfect so far. We missed to treat the deck with Boracol in autumn after the summer season and only refreshed it a couple of days ago in December, some nine months after the last treatment, when the weather was dry and not too cold. There were some areas of the deck where some green algae started to grow, particularly in shady areas where moisture sits longer. Still on the first 5l container of Boracol on our 46 ft boat – and counting…
Update November 2019
Just added another coat of Boracol, we also did one in Spring 2019 which used up the first 5l container. Again, after the summer season there were some spots with green growth in autumn which went away swiftly after the treatment. For us this is definitely the way to treat teak. application on a 46ft deck takes about 45 minutes. Quick, easy and efficient.