Sanding factory paint down to primer with 7424XP?

[BrutalGT]

Hello All,

I have been browsing these forums for weeks and picking up information and tips. I am painting my car and was sanding it by hand, but after realizing it would take me months to finish, I ordered a PC 7424XP and just received it today.

I went to Home Depot and picked up 100 grit and 220 grit sand paper, but the 100 grid didn't seem to be taking much paint off. I just went back, picked up 60 grit (they didn't have 80 in stock) but even after trying this, I am finding that it removes the clear but doesn't really remove much if any paint.

Granted this is my first time ever using an electric sander so I may be missing something, but it seems quite straight forward. Can anyone perhaps think of anything I could do to speed this up or any thing I may be missing?

1st try (with non-DA Makita):

2nd try (with PC 7424XP):

The Dark Grey is essentially where I want to get it to before doing my own layer of primer then paint correct? It seems to go Green -> Dark Grey -> Light Grey -> Metal, so I am guessing 2 layers of Primer. I have hit metal in a few small spots but overall I am just having trouble getting it to be consistent.

 

[allenk4]

Is you backing plate rotating or just jiggggggggling?

p60 should blow thru that

 

[BrutalGT]

Most of the time it seems to just jiggle. Having to kneel down was killing my knees and my back so I laid it up right and its more comfortable but it has made the jiggle a lot worse. Almost impossible to get it to actually rotate for some reason.

What causes that as it has been happening both ways quite severely.

*Edit*
Lowering the speeds from 3/4 down to 2 seems to make it actually do more but its leaving thousands of little swirl marks when its set that low. I am a bit frustrated as I ordered this specifically hoping to make this faster, why I hope this may have a simple fix

 

[goodinblack]

I personally never thought of a PC as a sander

Seems like bad choice

 

[geekdout]

Are you dry sanding or wet sanding?

Keep in mind the sandpaper you are using is really not designed for paint. 60 grit sandpaper should blow right through the paint and primer.

Make sure you are wearing some kind of face mask or respirator.

 

[custmsprty]

I personally never thought of a PC as a sander

Seems like bad choice

Quite the contrary, it was originally marketed and sold as a sander then adapted as a da polisher. It is still sold as a sander too in places like HD.

 

[BrutalGT]

Are you dry sanding or wet sanding?

Keep in mind the sandpaper you are using is really not designed for paint. 60 grit sandpaper should blow right through the paint and primer.

Make sure you are wearing some kind of face mask or respirator.

I am dry sanding (wouldn't trust an electric sander to wet sand). I was taking it really easy with the 60 grit for that reason but kind of stumped with how long its taking to make any progress getting through the paint.

After hours I have managed to get the main area done (the center in the pictures) but the sides are pretty curved. May try throwing some 100 grit pads back on and go over them some more.

 

[BrutalGT]

Just to provide an update (if anyone ever runs into the same issue) I actually stepped up the paper grit considerably to 220 and its working immensely better.

Why this is working is beyond me. I had 60, 100, 220 pads from Home Depot so I figured to try a jump. I can visually watch it sand away each layer now until I get to the primer and while slower than expected, its working 100x better than when using 60 grit.

I have almost finished off most of the center and left side with 220, but for testing sake I am going to try 100 on the right side. I have a feeling this will be a good balance that will speed it up and let me finish it off with 220.

 

[Andr3wilson]

60-80-100 are usually for shaping and smoothing out body filler. Even then they aren't used to much.

The reason for the finer working better, finer has more abrasive (smaller) content than a grittier paper. For this reason there is more contact with the paper and the paint. Pressure is more spread out. It seems counter intuitive, but the seemingly most aggressive is not always the best route.

Why are you sanding back to primer? What's the plan?

 

[BrutalGT]

That does make sense, although with absolutely everything I read mentioning to start with 80 grit to rip up paint layers, I would have thought that would be the way to go. I will be experimenting with 100 tomorrow to see how that works on finishing off the hood, but may wind up in the 100-150 range for the rest of the car.

I just have a 94 3000GT that has more peeling these days than it does paint. I don't want to dump a lot of money into it but would like to not be embarassed driving it so I am doing the "50$ Paint Job" with Rustoleum (it has ran me about 200$ after buying a 7424XP though lol).

I will just sand down to the base layer of paint for the rest of the car, the hood was my first piece and I was just kind of guessing as I went so the primer seemed a good layer to go.

 

[2old2change]

Curious as to why you want to sand down to the bare metal. The surface could be made smooth enough for a rustoleum paint job by simple wet sanding. The electric pc will do the job if a little caution and common sense is used. I have used a da many times to wet sand by misting the panel and soaking the paper before slapping it onto the bp. If you are convinced you want to go down to the bare metal then a liguid paint stripper would be my choice.

 

[BrutalGT]

It was basically just guessing since this is my first project like this (and not much online really states how far to sand down). For the rest of the body panels I will just be sanding off the clear coat and prime/paint over the existing paint.

So I finally just finished prepping the hood and sprayed a coat of primer on it. The basic little guide I am following says he sanded with 320, did a second coat of primer, sanded with 320 again and then painted.

Once I sand the first coat of primer (and later sanding in between painting) what is the best way to clean off anything that has been sanded? I used 50% alcohol/water before spraying primer, but curious what is recommended once primer or paint are already down.

Thanks for all the help!