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thinking about sanding, then polish

birddog486

Well Known Member
I'm working at polishing with Nuvite F7 and a rotary with wool pad but, I think I'm just spinning my wheels. The aluminum seems to have really deep grain and after 7 passes with F7 I'm not even close.

I'm ordering the F9 to give it a try but wondering if anyone has had to sand the aluminum to get a decent polish job.

This pic was after 5 passes with F7 and doesn't look much different after 2 more.


 
no sandpaper!

Hard to tell by the photo, but it looks like there hasn't been any polishing going on for whatever reason. There should be swirl marks from the rotating pad. Do you get good blackening when first applying polish? Maybe a bad batch of polish?
 
Don't sand!!

Been there done that.
Polishing is truly a very labor intensive endeavor and one that might not yield your desired results right away.
You'll need a box full of clean pads and a variety of compounds along with some
hard earned experience to achieve a truly brilliant finish. Once you do get the desired results, you can't wash the bugs off but instead must polish again to keep your bird nice and shiny.
Sanding will remove the alclad layer at least in some spots and the results will be very visible with a different kind of shine as opposed to areas where the alclad is still in place.
What you have is typical aluminum grain exposed and not easily polished down to a flat surface especially on places like the wing where you have a bit of wobble in the skin. Places like the upper fuselage are fairly easy to polish where the grain is opened up a bit by the curvature of the turtle deck and lends much more resistance to the polishing effort.
I built a polished RV 8 and had it for several years. Looking at that grain always bothered me and no matter how much effort I put in it, it never quite looked as good as the fuselage.
The guy who bought my plane promptly painted the wings but kept up the polished fuselage.
A well thought out combination of polish and paint might be your best option.
Good luck.
 
Birddog486,

Hard to judge from the pic but think I?ve run into your same problem, I haven?t fount the solution but F9 isn?t the answer. I?m guessing your aluminum is getting shiny and scratches are diminishing but there are small black lines/streaks instead of a pure mirror. I did try F9 on a few spots and no difference as far as the black lines/smudges were concerned. I had what considered to be some fairly deep scratches from the build process, F7 seemed to blend them out better then the F9 that just roughed everything up more.

Nuvite rep suggested C with the cyclo, it added a deeper polish of course but nothing for the black lines/streaks. Nuvite rep also said ?DO NOT SAND.?

A friend who rehabbed and flys a polished T-28 looked at my airplane/polish and thought the little black streaks/lines might be from the rolling process of making the aluminum sheet. He suggested sanding with fine grit and re-polishing.

Overall the polish looks good from 5 feet, if I ever get more time I?m going to sand a small spot and then rework with polish and see what happens. I need to hit the belly with some C first....
 
The pic was taken just behind the window on the curve of the fuse (only place I could get a good pic) but the majority of the surface looks like this. The side skins have what look like waves on the surface of the sheets, almost like the sheet was vibrating during the manufacturing process. It's a consistent bump across the sheet every 1/8" or so.

Initially the polish was making all kinds of black as it removed the surface oxides and, there's plenty of swirls marks also but, after so many passes with polish it's down to making just a small amount of black now as the polish does its thing.

I'm curious about the comments on not sanding. Are those comment from experience or just what you've heard? There's plenty of videos out there of sanding aircraft aluminum before polishing to help get down through the grain so a perfect mirror shine can be achieved.

I'm in this for the long haul so I'm doing whatever it takes, just looking for guidance from repeat polishers. I've got the F9 on its way so that's the next step I'm trying but I'm open to ideas.
 
experience

I see that you are determined to proceed and I remember that no one or nothing would have dissuaded me from having a polished airplane.
I can tell you from experience that sanding alclad is not a good idea.
I sanded one spot on my fuselage to get a scratch out and was never able to blend the finish with the rest of the polish job.
If you were to use non alclad like material that is used for shaping and welding
fairings etc. you could certainly sand it before polishing and attain a mirror perfect shine.
Unfortunately alclad has that grainy manufacturing pattern in it and from what I know some batches are worse than others.
The only way to get those lines out is to polish down to the lowest "grove".
 
I see that you are determined to proceed and I remember that no one or nothing would have dissuaded me from having a polished airplane.
I can tell you from experience that sanding alclad is not a good idea.
I sanded one spot on my fuselage to get a scratch out and was never able to blend the finish with the rest of the polish job.
If you were to use non alclad like material that is used for shaping and welding
fairings etc. you could certainly sand it before polishing and attain a mirror perfect shine.
Unfortunately alclad has that grainy manufacturing pattern in it and from what I know some batches are worse than others.
The only way to get those lines out is to polish down to the lowest "grove".

I think this is the typical situation which causes others to repeat sanding alclad is a bad idea (highlighted in red)

That's not what I'm thinking about doing. Obviously if there's a scratch that has a significant depth to it and you sand to the bottom of it your more than likely to be through the alclad layer.

Here's a video advertising Nuvite/Nushine where they start off with new alclad aluminum thats been scuffed and then sanding with 320 grit and moving up in grades before polishing.

https://www.youtube.com/watch?v=m35alBtVD-U
 
Don't do it

Alclad is a layer of pure aluminum, its sole purpose is corrosion protection. It is very thin, and will tolerate polishing for a long time if not over aggressive. Alclad has near zero structural significance, and sanding it away to expose the underlying alloy will only leave you splotches in the long run, and those areas will oxidize at a very high rate in comparison to the claded surface. Alclad is why so many unprimed interior skins don't corrode away , and its also how airlines polished their fleet for years..you will not find a polished Airbus though, as they do not build with Alclad skins...hence, Airbuses are always painted. Unfortunately, since Alclad is a bonded production process, there isn't a remedy to add or restore it once its gone..except paint. When we build our planes, the edges and drilled holes are where you will see corrosion first 99% of the time, simply because the clad is gone, and the edges are exposed alloy...thats why I advocate swab priming of every hole, and edge, but I have spent 40 years in the industry trying to prevent corrosion, so I'm a bit over the top!
 
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