You can get a mirror shine on either material, but for the longest lasting shine between buffing sessions, the stainless is the one to go with. Aluminum will oxidize the moment it's left to the open air and start to dull. Coatings can be applied (clear coat for an example) but it seems to kill the shine a bit. Stainless reacts much slower and keeps it's 'as polished' look for a lot longer because of it. Firewalls are notorious for being difficult to get at, so the material of choice is important. If you do go with the aluminum, look into the 'Alclad' variety. It comes in a lot of various alloys that are pure aluminum coated. The outer pure layer is only about 3 or4 thou thick, but protects the inner alloy from oxidization. The airplanes you see at the shows that are polished and sparkle, but get the constant attention that is needed to keep them that way. You don't really want to build something into it that is labor intensive and will make you a slave to it. I used a polished stainless firewall on an airplane I built years ago, it only required a swipe and wipe now and then to keep it looking respectable.
You can also clear powder coat. I did that on some pieces I polished then dropped off to have powder coated in clear. It's not AS shiny as mentioned above, but you never have to polish again, just a quick wipe clean.
Are there different grades of stainless I should look for? Hope this is not a stupid question!
There are a lot of different grades and alloy's of stainless. 304 is the base stainless that everything else is derived from. I think it's 311 and 318 that you see used for sinks. Which one is the one that will polish out the best? Don't know!! What I do know is the stainless I used was 65 thou thick and came polished with a protective plastic film. Peel off the plastic and it was like a mirror, but I don't know what grade it was. You may have to Google stainless and search out an answer that way. I'm afraid I can't help much with what would be the best, or easiest to use. Metal suppliers would likely have some answers for you though. Quite often they have little booklets with this kind of info available.
Just a bit of an after thought. The big rig trailers often have the back doors of trailers covered in polished stainless. Check with the truck parts guys and they would likely steer you to who would handle it or may know the grade of stainless involved. Traction truck parts may even carry the stainless sheet. Now you have your work cut out for you.
316 SS is the food grade with a film on it, it shines, that said it has almost a grain (brushed finish) but is shiny without doing anything but pull off the film, it scratches easily if your not careful handling it. most sheet metal shops can get it for you.
A guy I know had Plastic mirrors placed under his show car. It certainly was easier/safer than playing with glass. Depending on heat plastic mirror might be your answer.
the Kid
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#4 is your basic grain finish and 304 with a #4 finish is what's used for custom restaurant sinks.
Mirror polished #8 is also referred to as XL buff and has a slight grain to it.
Mirror polished #10, non directional, 304 stainless is what you want if you want a true mirror finish.
22 ga is 1.26 lbs/ sq foot and is .031" thick
20 ga is 1.47 lbs/ sq foot and is .037" thick
18 ga is 2.02 lbs/ sq foot and is .050" thick
Our cost is approx $4.00/ lb for the good stuff.
If you need someone to bring in a whole sheet, it would cost you a small fortune.
You need to find someone that has it in stock for the best deal.
