Black stains on bulkhead

[SAWDOC]

The bulkheads on my offshore 8 metre are sound but the surface has some discolouring from damp.

I had intended sanding and applying oxalic acid. However the bulkhead is made from some tough veneeered covered material that does not want to sand too easily.
Then i thought this material may not take sanding if it is only a thin veneer - time to consult the wise heads on the forum!

Anyone done this ?

 

[doug748]

The staining is generally under the varnish on the surface/in the grain of the timber.
I have just done a couple of bulkheads by using paint stripper. The first applications remove the bulk of the old finish, and subsequent work brings a sort of snotty goo off the surface revealing an increasingly clean veneer. Scrape in the direction of the grain with a blunted flat shavehook.
There was still some deep gain discolouration but at this point I gave up. By using increasingly aggresive methods you could no doubt bring it all out, but run the risk of veneer damage. I was happy to settle for a pretty good improvement.
Its a 1979 boat and the veneers appear quite substantial, even so I would not chance trying to sand it out.

 

[SAWDOC]

having removed the bulk of the staining would you then revarnish?

 

[patturner]

I had the same on a Seawolf. I sanded it down and applied 2 coats of varnish. It came up a treat!!

 

[doug748]

I settled for a couple of thin coats of conventional yacht varnish, which I will matt off later with a scotchbrite pad and Danish Oil. I will maintain it ,as needed, with a rub over with the oil.
Unless you want a deep gloss, I figure the less you put on the less you need to take off next time

 

[SAWDOC]

has anyone tried the oxalic acid to lighten the remnants of any staining post sanding?