Black Streaks in Plywood

[shemandr]

I built a dingy almost ten years ago. Over the years its developed black steaks under the finish on the deck plywood which is Okume mahogany. Today I spent an unpleasent hour removing all the finish. I think at least some of the streaking was moisture. They've faded with drying but will still be visible if I refinish bright.
What would be the material to use to bleach what my be mildew or just discoloration? Other suggestions?

 

[Time Out]

Try oxalic acid, aka wood bleach. This usually does a good job getting black marks like that out.

 

[CalebD]

Try the oxalic acid (1 part teak cleaner if you can't find it in the hardware store) first. There is also a 2 part teak cleaner that may work (or not).
If that doesn't do much you could try a light bleach and water solution on it which will kill mildew.
Teak and mahogany both start showing some grain or lines in them over time in the elements. Persistent moisture always seems to make it worse.
After treating the wood and lightly sanding before finishing I would rub some Tung oil on it and let that soak in for a day. Then rub Acetone over your work with a rag and apply the finish of your choice.
Mahogany can be a great looking wood on a boat so I wondered if you have any photos of this 10 year old dingy to share?
Good luck.

 

[shemandr]

Here are some pics. These are pre Oxalic Acid. I did try it but it didn't remove them. It lightened the wood and faded the streaks. Maybe its time to paint it.
The repair in progress on the floor is due to the dink being blown over this winter in one of the wind storms we had. I had it standing up leaning on the garage to keep critters from taking up residence inside.

 

[Buzzlovelace]

Oxalic Acid,works well is mild and avaiable at lumber and Hrdw Use gloves and let dry completely