Oxalic acid mixing ratios for iron stains on concrete

F9 isn’t Bob’s. The Harrison cat gets a lot of customers thinking they are supporting Bob I bet.
http://www.ptstate.com/forums/showthread.php?15080-F9-barc/page3&highlight=barc

The above pic is before oxalic;

The top of this photo was treated with 1c/gal,
The bottom of this photo was treated with 1/2c/gal.

Reckon I’ll be goin’ with a full cup henceforth!

Question: is oxalic OK on 1)steel lamp posts, 2)vinyl siding, and 3)galvanized steel?

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Really appreciate the tip to both brush out the oxalic and keep it wet for best results from squidskc. I am not finished with that sidewalk, but will wait until after the rain to retreat it.