Captain Ahab said:
Aluminum should never rust - it will get a layer of oxidation (looks grey not shiny) on it but not rust!
Oh, but aluminum WILL rust. However, it is only in the presence of Mercury (Hg). It will actually rust quite quickly and violently when in contact with a Mercury paste.
That's why you can't lawfully carry a barometer on a commercial aircraft, without a federal license. It could cause more damage to the aluminum plane than MANY other things.
i want to build my subfloor using some aluminum member from our old pool cage. they have the typical gray coating on them. these will be corrosion resistant right?. when i mount them to either the benches or through the sides what type of hardware should i use? bolts? screws? rivets? and should i use stainless? galvanized?
They should be fine. Use aluminum pop rivets, or stainless bolts/nyloc nuts. Do NOT use Galvanized. When you get to your deck do NOT use pressure treated ply. Both of these are great initiators of rapid dissimilar metal corrosion, which, although rather slow on many freshwater boats, is very rapid in saltwater, and in marina stored boats (high content of electricity in the water - speeds up galvanic corrosion).
im thinking small square patch of aluminum and 5200 sealant.
If the hole is small enough, put a rivet in it. Solid rivets are ideal, but pop rivets make excellent hole sealers, coupled with a little 5200. If it is a larger hole, I would cut a round disk of aluminum (corners on the square would hang up on things, and try to tear off the patch), and rivet it on with a series of 3/16 pop rivets and 5200.
i want to start sanding down the old paint but if i dont paint it right away will the aluminum rust? or will i have to re sand it?
It will start to oxidize immediately. That being said, there won't be a significant enough amount of oxidation to worry about for paint adhesion for 2 - 3 hours. But, you cannot expect to wait any longer than that to paint after prepping.
Believe it or not, there isn't a better sealer of aluminum than it's own oxidation, so unless you want the "look," just leave it bare, and let chemistry run it's course.