galvanised steel screw stains

[bkel]

Hi all, long time since posting anything, been flat out down here!
I have had a builder mate of mine wanting me to fix up some stains to one of his clients deck. They had a backyard operator clean it but the galvanised screws have leached a stain onto the decking( around the screws), it looks like ink. Would Oxcylic acid remove such a stain or will I need to go looking for something else?

 

[john orr]

Oxalic would be my first choice. I know that it works for galvanized screws used in fences.

 

[archie_MN]

You're looking at zinc stains. Oxalic and neutralize.

 

[Torque454]

I thought oxalic was the neutralizer?

 

[archie_MN]

Add a base like like bleach to neutralize the acid. Without a neutralizer the acid just will keep eating. If you're not sure about your runoff, ph meters are like $20.