----- Original Message -----
From: "Hammarberg, Eric" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Wednesday, May 22, 2002 1:06 PM
Subject: Stainless Steel and Mortar


> I have a 70-year old building in New York City with type S 30200
nickel
> stainless steel counter flashing. Is there any reason to think that
the
> mortar could have damaged the metal?


Eric, if muriatic acid were used to wash the mortar, or at any time
chlorine fumes or any other strongly acidic or strongly alkaline
substance were in contact with the flashing, it could have had an effect
on the st stl flashing. I have seen what customers claimed to be "rust"
on first quality stainless commercial toilet room accessories, which was
brownish corrosion, but wasn't rust. It looked like rust; in other
words, there had been some oxidation of the iron, but it was caused by
cleaning chemicals, not water. I have also seen some high nickel alloy
stainless (which is used for st stl mirrors because of its hardness --
it will take a high polish) discolored and damaged by unknown cleaning
chemicals. Even the oil from hands will discolor st stl toilet
partitions around the door hardware if the partitions are not siliconed
or waxed every once in a while -- we call it "blue-ing" because the
discoloration is bluish, and the discoloration is permanent, meaning
that a chemical reaction has taken place.

I guess my point is that stainless is famous for not rusting, but that
doesn't mean it's not reactive and won't easily corrode or degrade. Is
it possible that air pollutants have found their way onto the surface of
the building, perhaps by dry deposition, and then in a light rain,
become concentrated and washed down onto the flashing time and time
again over the years, damaging it? (or reacted with something in the
mortar, to form a compound that could damage the flashing?)

deb

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