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that's not stain!!!
That is a homeowner with a home depot pressure washer and the wrong size tip,no knowhow,no chem, and no chance of getting this right.
This is what happen's when you try to wash a deck with a 20 deg tip.
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Bigboy it's not going to be easy to blend in the wand mark's on soft pine.
SSpray it with a mix of percarb bleach,surfacecent,and soda ash.
Let dwell and wash with a 40 deg tip at about 4 inc's from surface.
Then ,when done,spray it citric acid or oxalic acid to brighten it up.
If i needed the work i would try for $300.
It would be worth it to them to fix their screw up.
The brown is the wood that has had the old wood fiber's stripped away.
Man ive some homeowner mess-up's but WOW.
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My price DOSE'NT INC. SEALING,SANDING NAIL SETTING,OR imply i can fix this 100%