If the teak is used for decking, I recommend leaving it age naturally with no treatment. Just use salt water
and a soft brush or sponge (brushing across the grain) to keep it clean and looking good. If the teak is a trim material, I recommend using Cetol. Clean the teak well, let it dry for several hours, and wipe with acetone to remove the first layer of natural oil
. Apply 2 to 3 coats of Cetol natural teak colour, followed by 2 coats of Cetol gloss. Sanding
between coats is not needed (just rough up lightly with a "kitchen scrubber") if you do the coats one after the other. Then annually apply a coat (or 2 depending on condition) of Cetol gloss for maintenance
. Do not use the Cetol (gloss) for floors.
Mine has been on now for about 3 years and looks great!
Oils tend to attract dirt, mould, and other things that will cause the teak to turn a "black" colour. Then it will require a complete starting from scratch.
I do not profess to be any kind of an expert, but this has worked well for me.