If you are ever looking for a Teak specialist. I do not hesitate to recommend Jeff Howe for Teak Decking, Interiors, Swim platforms, Steps, and Trim.
Here is his advice on Periodic Cleaning of the Teak:
If you feel the need to spruce up the deck beyond your usual brush and soap/water, you may want to use a two part teak cleaner.
DO NOT. Two part cleaners are usually made from caustic chemicals that although clean very well, remove or soften the grain in the wood. This, causes the need for sanding more often and considerably shortening the life of your deck. Here is a great way to use a two part cleaning system that is very gentle on the wood, harmless to your seams, and biodegradable.
Available at the grocery store, is SUDSY AMMONIA, and WHITE VINEGAR. The ratio is roughly 1:1 SUDSY:WATER, for part one. Use a Doodle Bug Scrubber attachment for the Shurhold Pole, and a green pad. This should be available at your local marine store. Use this mixture liberally on a wet deck, and keep wet throughout the process.
Scrub AGAINST the grain whenever possible. No heavy scrubbing is necessary. Once complete, rinse the products thoroughly with fresh water. Clean the Doodle pad very well and use the vinegar direct and alone to “brighten” the deck.
This is only spread over all wood cleaned, and is not used for scrubbing at all. Once all the wood has been coated give a few minutes to soak in. You will see a change in color to a brighter more amber hue. Rinse the Vinegar liberally and the deck is clean.
When it becomes necessary to sand the deck, it is important to use a light grit and ensure it is done evenly. We recommend 100 grit sandpaper for maintenance sanding. It is very important to mask off any areas of paint that may be accidentally bumped by the sander.
The use of a random orbital sander with dustless attachment is preferred over any belt or high-speed sander. Keeping the sander moving across the grain, seams and wood evenly will ensure a level sanding.
Keep in mind that sanding is not even recommended within the first year or so; however, that is owner’s discretion. After the first year, once every 12-18 months will ensure a long life to your deck.
Boat/Yacht Teak Installation, Repair, and Maintenance - Teakworks