to something that I can claim expertise (metallurgy)... (sorry for the
length)
All the chat about galvanic corrosion is correct and copper and aluminum
isn't a good combination, but you're kind of stuck. You have to drive metal
fasteners through the board into the aluminum. The last thing you want is a
non-stainless steel (galvanized or no) in contact with aluminum. That's your
first concern because the steel will corrode and with the large relative
area between the aluminum and steel, the active part of the galvanic cell,
the screw will experience accelerated corrosion.
Having said that, though, the correct environment has to be present:
moisture and an ionic specie to make the moisture conductive. You can assume
that these are always present, but take measures to minimize the environment
and promote drying.
1.) spring for the stainless fasteners, at least on the ledger board, unless
you can get under your deck and periodically inspect a fastener or two for
corrosion and replace as necessary.
2.) I don't know about the specifics of the acq and aluminum, but as
suggested, you could put a non-porous shim between the aluminum an the wood.
A few layers of 2 liter bottle would work in a pinch. You can't avoid
electrical contact due to the screws, but the shim's intent is to promote a
dry interface between the aluminum and the wood. Consider caulk at the top
of the ledger board where it meets the house to keep water from going down.
That is your best defense.
In the end to prevent corrosion, make the materials compatible with the
environment or change the environment. Corrosion is a fascinating topic.
Good luck with your deck!
Joe
(an occasionally surfacing lurker)
(keep the "geek" comments to yourself, I'm a card carrying nerd 8^)
----- Original Message -----
From: "Ben Doom"
> When two differing types of metals are in contact, they tend to
> chemically react, creating an electric charge and corroding both metals.
>
> This is why knives should be stored in knife blocks, by the way. It's
> also why the clamps on your battery terminals should be tight -- to seal
> out air and prevent corrosion between the clamp and post.
>
> Wow! I finally knew something useful!
Geek. :-)
I actually knew that. It's why I've been buying hot-dipped galvanized nails
and wishing I could afford stainless steel. The stainless has significantly
less galvanic corrosion.
-Kevin
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