removing tannin stains on new deck

9 years ago

We built a pressure treated deck last summer. We kept a redwood picnic table on the deck, and noticed where the table was, black stains appearing on the deck. We moved the table to another side of the deck, and then the black stains stated appearing there. After doing a bit of research we learned that the nails in the picnic table reacted with the wood and caused the black stains, I think they are called tannin stains. I need to remove these stains before we can stain the deck. Will a wood brightener, such as Defy, work? I've read it is good for cedar and trex type materials, but nothing about use on pressure treated wood. As I understand it, it is the oxalic acid in the wood brighteners that remove the stains. Can anyone advise me on this? We removed the picnic table, but we still have the stains on the decking, I don't want to use a solid stain just to cover the stains, I want to remove them and then stain with a semi transparent stain. What is the best way to get rid of the stains? I've tried cleaning them with soap and water, it didn't do a thing. Help!

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Comments (5)

kudzu9
9 years ago
Oxalic acid is the standard means of trying to remove such stains, regardless of what wood it is. However, bear in mind that it doesn't work equally well on all woods. It may get rid of most of the stain, or not, and it may also affect the wood in such a way as to cause a light spot when you go to stain. It's worth a try, but don't expect a perfect result.
lam702 thanked kudzu9
bobismyuncle
9 years ago
Oxalic acid is not a "spot treatment" I'd do the whole board to prevent a light "spot" Here are some directions and information: http://www.woodcentral.com/bparticles/woodbleach.shtml I believe _some_ deck brighteners are oxalic acid (others can be Sodium percarbonate
(like Oxyclean) that generates hydrogen peroxide when mixed with water. Check the label or MSDS.
lam702 thanked bobismyuncle
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lam702
Original Author
9 years ago
I tried using Barkeepers Friend (which has oxalic acid listed as an ingredient) on one of the stains. tI did remove the stain, but there is now a bright spot where the stain was. I just wanted to see how well the oxalic acid works, it seems to do a good job. I think and hope that by applying the wood brightener to the entire surface of the deck, the spot should blend in, as the rest of the wood lightens too. After reading so much about deck stains, I don't want to have to use a solid stain if possible, I'd prefer a semi transparent so the stains/bright spots need to go. Is the sodium percarbonate better than the oxalic acid? If possible, I'd prefer to use whatever is less harmful to the surrounding grass, plants and bushes.
lam702
Original Author
9 years ago
Just to update, I used the brightener on the entire deck, I had to go over the floor boards twice which lightened the stains a great deal, although didn't completely remove them. They were light enough that I felt they wouldn't be noticeable once stained. I chose Armstrong and Clark driftwood gray semi transparent stain, just finished the project yesterday and it looks great. The tannin stains are not visible under the new stain color.
kudzu9
9 years ago
Thanks for the update. You must have done a good job because stuff like this is hard to make unnoticeable.