Spots from sanding aluminum

[rbmgf7]

I'm trying to finish this raw aluminum sign. It's 3003. It'll get clear coated once finished.

I'm using an electric random orbit from 80, 120, 220 and I've been getting a good matte finish but suddenly these spots started appearing. I though it was oil so I wiped it all down with acetone but it doesn't help. I stepped up to a finishing sander so I wouldn't remove any more than I have to.

I can sand one spot away then more will show up. I've polished aluminum before but never had this happen.

Any clues on how to get rid of these spots?

[rbmgf7]

I tried wet sanding and it seemed to help a lot.

Found a pretty good median for finishing aluminum: Wet sand with the random orbit up to 220. Leaves a nice, even swirl.

I tried to go into finishing up to 1000 but there were evident streaks.

[Largemouthlou]

I have seen that a lot and I think it is the metal composition that they add to aluminum anf it is not blended right.. I believe it is magnesium spots. I have found it will sand away,, I normally use the burnishing sander to do a satin finish on aluminum I clear coat.

[rbmgf7]

Yeah, the Metabo burnisher has been sitting in my Amazon cart collecting dust #oneday

[hsolve]

^^^ Well then what are you waiting for just dust it off, compressed air works great!!!

[little blue choo]

I use a Eastwood Contour SCT and always get a great finish. Just remember DO NOT use a wheel on Alum. that was previously used on steel. It will imbed steel into the surface of the Alum. and you will wind up with rusty Alum. Lesson learned the hard way. https://www.eastwood.com/eastwood-contour-sct.html

Rick