There will be lots of opinions and advise on this subject!! I've always understood that you have basically two choices: Teak Oil OR Teak Sealer, if you want to enhance the wood look but do not want to varnish or apply Cetol. Teak Oil keeps the wood grain looking fresh, but it breaks down and needs to be reapplied every few months - more often if it is exposed to sun. A Teak Sealer will provide a stronger and longer lasting barrier (up to a year or so), but it breaks down in splotches, causing you to have to sand the entire thing in order to reapply and keep it looking nice. Looking at other peoples experience, it seems easier in the end to simply rub on more oil every few months than to sand and reapply sealant every year. If I were you I would apply teak oil until the old teak stops absorbing it. I wouldn't consider a Teak Sealer until it's really absorbed a lot of teak oil. However, I prefer to oil the teak whenever it needs it rather than sealing it.........that way you never have to sand and you are replenishing the wood as it needs it. You might find this article helpful.
Well maintained teak woodwork is highly prized and boat owners want to do everything they can to keep it looking great.
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