Removing wood Stains (Black Spots)

[Jack Tar]

Get yourself to the local hardware store and purchase a container of Oxalic Acid in powder form. When you apply it to the area of damaged / satined wood make a wet paste out of the powder and apply it to the stain. Let it set for a while. Wipe of the paste and rinse the heck out of it with fresh water. Let it dry and apply what ever finish to it you need. Match to the existing wood by using wood stain color to match and then final finish. Be careful with the acid as it can damage other surfaces . This process is known as bleaching and you can do small areas or whole sections. Take your time and dont hurry.

[Captain Smollett]

I've read that oxalic acid was very bad for the soft grain in teak?  Some teak cleaner products have oxalic acid in them, and overuse (maybe that's the operative word) cause decay of the soft grains.

This leaves the hard grains "raised" and the surface left with a rippled texture.

[Dougcan]

You are correct capt'in, but it beat the alternative, which is sanding the thing down paper-thin!

This way, you can remove the stain and after it all dry, give it a light sanding and finish it.

Sometime it's a tough choice, especially if there's not much wood left.

[Amorous]

Min-wax makes a filler specifically for open grained woods like teak and mahogany which you can color to your needs and prevents sanding away all of the proud wood after bleaching.  It is very easy to use and is good for both interior and exterior applications.

[Jack Tar]

I agree about the caution may damage wood. It's not something you want to do on a regular bassis. But if you have damaged stained woos in a small area you must weight the risks and amount of work you want to undertake.