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SANDING ALUMINUM SHEETS

I am finishing sheets of 5052 aluminum with an random orbital sander. First pass is with 60 grit sandpaper, second pass is with 100 grit. I am trying to achieve a rough brushed look with no discernable grain or pattern. This works very well for me but sometimes I am left with some shiny marks in large patches or in fine spring shaped spiral patterns that I am guessing are left by the sander. These marks become visible in the 100 grit pass, and more visible if I try to step up to a finer grit. Sometimes the marks don't become apparent until the sheets are post coated with lacquer. Does anybody have any idea how to avoid the shiny spiral marks, or remove them?

thank you.

Roy Barloga
studio - Oakland, California, United States
2006

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I think--magic word is think-- that the finer sandpaper is crosswise to some of the deeper gouges from the first paper and parallel to same. The crosswise areas will tend to be smoother or more polished or less rough while the parallel areas will basically remain coarse and thus show considerably more.
You might try using only one paper of average grit and see what happens.
Another possibility is to put a new fine grit paper on and re-sand it a second time. The paper fills up.
If it is an air sander, you might try wet and dry paper and sand wet. (rinse very well if you do)

James Watts
- Navarre, Florida
2006

Try using dedicated sander with oil resistant rubber pad or felt pad using mineral spirits ⇦ this on eBay or Amazon [affil links] as lubricant with wet dry paper. Shiny spots can be from burnishing from clogged paper. Also Stearated paper and air hose also(dry) can be used with blowing off paper regularly. Also try Mirka screen abrasives too(dry) with vac sander and/or compressed air cleaning as above.

Norm Stavin
- Amagansett, New York
2007