Iron Stain Treatment
Oxcon (oxalic acid concentrate) is the only effective treatment for rust stains from around nails, spikes, and screws.
Oxcon comes as a concentrate that is diluted with water prior to use. It is best applied using a garden type pump-up sprayer but a brush or broom will also work. Apply a liberal amount to the wood, let it work on the surface for 10 to 15 minutes and rinse it thoroughly with clean water.
Oxcon should not be used for spot cleaning since it may cause blotching of the surface.