Brown stains and streaking after using oxalic acid

[Irish Rover]

I washed the deck last week using oxalic acid powder diluted to 10%. I now have areas of brown staining and streaking where I didn't have before. What caused it - insufficient rinsing? What's the solution? Advice appreciated.

 

[Caladh]

I washed the deck last week using oxalic acid powder diluted to 10%. I now have areas of brown staining and streaking where I didn't have before. What caused it - insufficient rinsing? What's the solution? Advice appreciated.

I had similar last year. I think the Oxalic solution was probably too strong. It took some elbow grease to get rid of the streaks with light compound.

 

[rotrax]

After reading this posts headline, I thought for a moment you had drunk it!!

"Brown Stains and Streaking indeed!!!!

 

[Hoolie]

I've had similar not on the boat but on a metal garden table. My assumption was that the colourless ferric/ferrous oxalate reverted to oxide in bright sunlight. Tried again with more thorough rinsing and it's now ok.
On board I always thoroughly rinse oxalic as we have our cat prowling round the decks!

 

[doug748]

I usually apply it with a hand spray in a saturated solution and lay it off with a brush. The only staining seems to be when I have applied it unevenly and I give it another quick go.

 

[William_H]

I use oxalic acid on top sides. When it runs down to antifouling paint it does discolour the paint. Not such a concern as a/f is covered again. So if your decks are painted it may be the oxalic is attacking paint. Don't know a fix except repaint. ol'will