Scratches showing up after cutting - How?

Discuss anything after that final masking comes off.



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PostPosted: Mon Jul 26, 2021 8:35 pm
Hi,
Painted the hood of my Corvette recently and looked OK at first, but after cutting, I am getting nasty scratches in the finish. Seems the more I cut, the more the scratches show up.

A bit of background…

1. Started the hood with Evercoat filler, and some fiberglass repair
2. 2-3 coats of Feather Fill G2, blocking it down, and leaving final coat un-sanded for 4-6 weeks.
3. Final blocking of Feather Fill with 400
4. Sprayed with Omni (PPG) sealer, base coat, and 2 coats of clear.
5. Was doing this in garage and clear was rough. So waited a week and blocked clear with 400 and reshot two more coats of clear. Looked good.
6. Waited another 4 weeks before wet sanding and cutting

Finishing:

Wet sanded with 1500 and block. Looked solid and flat. But now cutting with Meguiars 105 compound and a cutting pad and getting big scratches in the finish.

Have no idea how this could happen as I should have eliminated any shrinkage issues, and those scratches look like 80 grit scratches, when sanding after bodywork was 220 to 400 to 600 grits before applying the sealer. And the Feather Fill should've filled any issues without shrinking.

Any ideas on what is going on here? Can I save this clear?

Thanks in advance.

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PostPosted: Tue Jul 27, 2021 1:59 am
Surface or paper not clean >> grit between paper and clear >> deep scratches.

also,

Sanding with P1500 and expecting to get a mirror finish from buffing once is wishful thinking, as is expecting clear to fill P400 scratching.

Re-assess to be sure scratches are in surface, not under last coats of clear (you may be lucky here with a solid colour). Recut with clean P1500 then go up through the grits P2000 and P3000. Then buff.
Chris

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PostPosted: Tue Jul 27, 2021 8:38 am
Switch to Meguiars M-100 and a twisted wool pad. Those scratches will come out.
The M-105 has fillers in it that make the surface look good until it's cleaned. I used it for years until I tried the M-100 and have never looked back.

Like Chris said, it only takes a small bit of grit or dirt to get trapped under your sand paper to put some deep scratches in there. This is why you should follow up with finer grit sandpaper. I generally use 1000, 1500 and 2000 when wet sanding. The 1000 is done using a hard block to be sure the surface is flat (no wave or orange peel) then the others are done on a soft block. 1500 to remove the 1000 scratches and the 2000 to remove the 1500 scratches.

Personally, I tried Omni products one time and moved on. They are cheaper for a reason. Much better products out there. Keep that in mind for your next project.
1968 Coronet R/T


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PostPosted: Tue Jul 27, 2021 8:51 am
I'd agree with everything said so far but if you indeed only have 2 coats of Omni clear on there watch out.... I would concerned about going deep enough to get those scratches and boom! you'd be through that clear..... That is not a high build clear to begin with.....
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PostPosted: Tue Jul 27, 2021 10:33 am
all GOOD info above. you have dirty paper or surface, you must be squeaky clean. be careful where you put your hands, anything you touch may be dirty one small grain of something is going to cause what you have. use a tack rag before you start. i use a bucket of water with a drop of Dawn fill the bucket almost full i wash my paper and hands first. i use a spray bottle and a clean rag or squeegee to clear the area so i can see what i'm doing. quality of paper makes a difference.
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PostPosted: Tue Jul 27, 2021 10:55 am
thanks for the info. Seems the consensus is that these scratches are likely in my sanding and cutting processes, and not due to some flaw in the overall painting process. If so, that is great news as I can address the issue vs. just being incredibly confused.

Thanks,
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PostPosted: Wed Jul 28, 2021 5:59 am
like everyone is saying the scratches look like they are coming from your color sanding.
one thing I'm not seeing people recommending is to pre soak your wet sand paper for 20 minutes in water before you start to sand.
this softens the backing of the paper making it more pliable not to get hard creases in the paper.
as stated everything needs to be clean!
also use lots of clean water to keep washing off everything importantly the panels your sanding.



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PostPosted: Wed Jul 28, 2021 9:21 am
Thanks again everyone. Will go after this with a different approach...

Re-sand with 1500 and block, being much better at keeping everything clean and wet. I was not great at that, even letting things get a bit dry and using cloudy water from a bucket. Keep going to 2000, then 3000.

Also, was using a D/A with a foam pad and Maguire's 105. was told I that is not great for getting out scratches and that I need to get a rotating polisher with wool pad to get it cut/polished.

Does that sound correct?

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PostPosted: Wed Jul 28, 2021 10:31 am
Yes.
Remember you don't have a lot of clear on there.
If it were me, I would try the rotary buffer with a twisted wool pad and Meguiars M-100 first.

Start the rotary buffer at a slower rpm and work back and forth across those scratches. Then you can bump up the rpms to 2000 or so and buff. Be sure to keep the rotary moving so it doesn't sit in one place and overheat the clear and burn through.

Whenever you approach an edge or body line, make sure the rotation of the pad is going "off" the edge and not "into" the edge or it will grab and burn through.
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PostPosted: Wed Jul 28, 2021 8:46 pm
'68 Coronet R/T wrote:Remember you don't have a lot of clear on there.


btwick wrote:4. Sprayed with Omni (PPG) sealer, base coat, and 2 coats of clear.
5. Was doing this in garage and clear was rough. So waited a week and blocked clear with 400 and reshot two more coats of clear.


By my calculations that's 4 coats. Even with the first 2 being a bit dry, should be enough.
Chris
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