We have 18ga 304 stainless steel hollow fabricated letters mounted to a 6063 .25" Aluminum bar with Stainless fasteners. I'm less concerned about the corrosion at the point of connection. This is mounted to the top of a slight overhang above a door and is up against a brick facade.
The problem is that the letters started to discolor.
I claim that the brick above was washed (as it looks in pictures) with "something" that rained down on the letters and caused them to stain. The staining looks like hard water marks and a bit of rust. The client claims that no cleaning of the bricks has occured and that the chemical reaction was caused the by a reaction of disimilar metals. I'll agree that at the point of connection there is some oxidization but these letters are 12" high and there is corrosion on top of these letters.
We've reinstalled a new set of letters in the same manner and are now playing a waiting game.
Any ideas as to if the letters could have been stained 12" away from the contact point - by a metallic reaction?