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Well today I finally learned how to correctly color sand and buff out a finish, after sanding and buffing out 4 paint jobs over the past 5 years. I've been doing it wrong, resulting in hundreds of hours of extra work, extra material, and finishes that are not the clear, haze-free glass-like finishes other cars have. I was at a different paint store than my usual and the guy there gave me a primer on how to cut and buff finish.

First, you do NOT use the coursest grade of sandpaper to flatten the paint to what you are looking for, which is what I have been doing. Indeed, the flat, smooth, surface does not appear until you are at 1500 grit. Here is the the zen of sanding out finishes.

Each sanding exercise puts scratches in the paint, represented by drawing a "v" on a piece of paper, with the top of the "v" at the surface of the paint. The courser the grit, the deeper the "v". If you do not completely sand the surface down to the bottom of the "v" a trough remains. thus, as you sand again with a finer grit, you are using a shallower "v" to cut down to the bottom of the prior grit's "v". This means that you are worker harder with a finer grit to remove more material, with each pass. It is difficult to cut down far enough to remove the earlier sanding scratches completely. This leaves very fine scratch marks which collect buffing compound, creating a haze in the surface.

To test what you have on the surface, lightly mist the surface with a 50-50 mixture of water and alchohol. The alchohol disolves the compound, just leaving the scratches. Then, position a high intensity work light at an angle to the surface and look across the surface. Any scratches will appear.

The correct way to sand out the finish is to start wtih 1000, or possible 800 in an extreme surface condition, and just use this grit to knock down the high points in the paint. Move up in grit by 200, say moving from 1000 to 1200, and knock down the high points some more. Move up again to 1500 and use the 1500 to completely flatten the surface - no more orange peel. You can sand again at 2000. Heck, there is a new sanding disk product out which is a foam pad that has grit to it, rated 3000. This actually polishes the surface. After all this sanding, you move to the wool cutting pad and compound to get rid of the 1500 grit scratches.

As for sanding, a DA orbital sander is not the way to go. The DA pad is set at a very slight angle in that the pad rocks up and down slightly as it rotates. This leaves a very slight imperfection in the finish that looks like a "wave" when seen at an angle.

The ideal tool for this sanding is considered to be a round, 6-inch finishing sander, the backing pad of which is flat to the surface. If you use a Double Action (DA) orbital sander, there is a method to compensate for the up-down wobble. You use an "intermediate pad" between the backing pad and the sandpaper. This is a foam piece of close to a 1/4 inch thickness. The foam pad absorbs the wobble and allows you to get the paper flat against the surface. Supposedly, it also allows you to float the tool over body lines and not cut through the paint.

Tomorrow I purchase the sandpaper, in boxes of 50 sanding disks each, plus the intermediate pad, and also get my DA checked out to learn whether the bearing is bad. After that, I can finish sanding out the 66 using the new technique and see how it turns out.

Call me an idiot, but I never learned this before. What a lot of wasted time, money, and emotional energy over the past 5 years. Glad to learn the right way to do it as I have 3 more mustangs to paint. . . the 69 sportsroof, 65 fastback, and the 70 sportsroof.

I hope this information helps someone avoid my heartaches. :D
 

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Wow, good info, Ken. I have one correction to your post, though. You have 4 cars to paint if we count my sportsroof! ::

Seriously, that's some great info, and we do need to get together now that my tile is all in and trade helping each other with the body work on your cars and Scary.
 

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Personally I prefer to only use 1500 grit and do it all by hand. I do not use a DA because it's too easy to burn through a paint job. I can sand and buff a complete car in one day using only my muscles. (and a high speed buffer) I will use 1000 on really bad areas and sometimes 2000 on dark colors. I feel the DA process is really only nessary for high productions shops. Plus it takes time to learn to do it correctly. You can ruin several paint jobs before getting it down.

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Mano man... you should've just asked me about colorsanding at knotts ;) I could've saved you even more time :D I have the makita http://makita.com/tools_Item_View.asp?id=257 it works great. I still color sand by hand (and long board) with Meguire's wet/dry sand paper (works best IMHO). THen I cut and polish with the 3M then procede onto the 3 step meguire's system.

here was after colorsanding and then cutting/polishing by hand and a cheapo autozone buffer:

http://www.desertmustangs.com/1972coupe/Polishing/PS-Fender-Before-3.jpg

With the Makita:
http://www.desertmustangs.com/1972coupe/Polishing/PS-Fender-After-1.jpg

I used the Meguire's 3 step, #9, show car glaze, and then the carnuba wax. It's lasted a year so far in the hot AZ sun.

BTW the makita is not a DA sander, but can burn through the paint if not used properly.
 

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Discussion Starter #7
It was hot, I was tired, the paint was course as sandpaper, so at one point I used a 340 grit sanding screen (big no no) generally I started with 400 or 600.
 

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Oh no, that just sent a chill down my back! ::
 

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WHOA, 400-600 is what I used to finish of my my build primer and sealer. Clear was 1500, then 2000, then Meguiars medium cut compound, then Meguiars fine, 3M FinesseIt II and finally Meguiars #2 swirl remover. All wet-sanding was done by hand/flatboard. Polishing with my variable speed polisher (set low).
 

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I had serious orange peel on several panels, I tried 1500 and soft sanding block, which did not eliminate enough "peel" I had to resand with 1000, which helped, but left too many scratches. 1500, 2000 eliminated the scratches (after hours of arm work) and then used 3m perfect it II rubbing compound and a Yellow foam pad 1650 rpm polisher, this brought the surface to a nice luster. The final surface will be gone over with 3m swirl /scratch remover and soft foam pad (havent done this yet) probably just on top surfaces. I was very nervous NOT to go too deep. I didn't want to repaint.
 
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