Howdy 914world, looking for some feedback and advice.

I painted my car myself using PPG Concept single stage urethane in Mexico Blue (code 336). This paint was not cheap stuff, but I made sure to put 3-4 wet coats on everything so I'd have plenty of margin to come back after and flatten the peel. I was also under the impression that the color I chose was a solid color, not metallic or pearl. However, I did notice when spraying that there appears to be a very small amount of sparkle in the pigment, which is extremely noticeable if you screw up and paint a run.

When I put the last coat of color on my doors, I did exactly that and screwed up with a big run. Frankly, I was rushing and my brain was working a half step ahead of my hands. Anyways, I thought I might be able to sand the run out later as I've seen many times on other projects and YouTube videos.

Here is a picture of the run:


Long story short, I've run into some issues when wet sanding and buffing out my paint job. It seems I've sanded through the top layer of color in a couple of places. I'm not new to paint correction but maybe I have been misinformed all of this time. I thought the point of spraying many coats of color was to leave a safe amount of paint to sand off afterward when removing orange peel. Is this bad logic?

For what it's worth, I'm sanding using 2000 grit paper (1500 in some places, if needed) and able to correct sanding marks with LCC yellow pad on a long throw DA. I thought I'd need my rotary but the sanding marks are coming out easily with Menzerna Heavy Cut 400 on the DA.

However, it's clear that I've sanded through the top layer of paint and that the layer underneath does not match. There's also a darker ring of pigment around the transition between the layers.

Here is a picture of the door. The light spot, to the bottom right of the camera flash, is where I've gone through the top layer.



I've also rubbed through the top layer on an apparent high spot in my front hood. Here is a picture of that. You can imagine how happy I was with myself with I noticed what was going on.



I haven't had issues anywhere else on the car, but it's clear I'm going to have to have these two pieces re-sprayed. I'd do it myself but no longer have access to my "spray booth" and pretty sure the VOC paint I used is considered contraband in California.

My question is - what exactly is going on here. Am I sanding way too much off? Is there a color match problem? Is my paint actually not a solid color? I want to learn from my mistakes so I don't continue to make them on this very time consuming and expensive paint job.

Thanks

Many people feel you don't color sand single stage. The solid colors tend to move to the top so if you sand it, you are removing the most important layer.
@rick 918-S

I don't have any advice but man that sucks; I feel for you. I've spent hours wet sanding on my clear coat

First of all, you're a brave and talented man to be doing that job. And the Mexico Blue is just superb. Great choice!

I had that exact thing happen on a guitar we were building where the 'polish stage' sent us right through to previous layers. It was a sad day, following 8-10 coats of color to have this happen.

Mepstein's point about the solid color rising may be true. (I can't debate nor confirm) In my case, I had to sand back down to and recoat. Of course a guitar is more manageable and I feel bad if that's where you have to go to finish out that car.

Hopefully someone here will have more encouraging advice. Just keep the goal in mind; its going to turn out incredible.

I also thought I read somewhere to avoid color sanding into any metal flake as well since you would be altering the shape or profile of the flakes thus creating color problems as well.

I just finished painting my car in my garage myself as well.

I color-sanded my single stage urethane paint (Shiny Primer Gray-not an official Porsche color) and sanded thru in a few spots. I repainted the panel. It was a PITA but it was the right way to do it. My paint was not metallic at all.

Do it by hand, not with a machine. You can feel the surface better. You are also less likely to sand thru. I used Durablocks of various sizes, 1000-1500-2000 grit. Then I polished with Chemical Guys V32-V34-V36 using a TorqX polisher.

For a paint booth, I made one. I used 2x2's and plastic sheets. I used box fans to move air. I had furnace filters as well. Was it perfect? No, but it kept the chunks out. I made 5 panels that I could bolt together. It's relatively easy to take up and down and store. I'll post a picture later.

I live in LA and you can paint up to 3 gallons a day and be ok. HVLP sprayguns are exempt. Just be cool about it to not attract attention.

Our shop painter said 3-4 coats isn’t much. Especially if the paint isn’t top of the line. He said you don’t want to color sand single stage if you don’t have to but if you are a newbie, you might have to. Never sand metallic.

He suggested spraying some test panels with and without sanding so you can see the differences.

Interesting, I haven't heard this before but could explain what's going on here.



Definitely, have read/heard this. I'm still not convinced exactly what this paint is. It looks like a solid color to me, but then again I've seen a slight metallic sparkle in the pigment when it builds up. Who knows.



Definitely agree with this and have been sanding by hand with foam blocks



Good to know. Can I still purchase non-VOC compliant paint out here? The stuff I sprayed it with (PPG Concept) was definitely not "low VOC"



Good advice, this is why I went for the "upgraded" paint and picked Concept over Shop Line. I'm not sure that the number of coats really mattered in my case seeing as just sanding through one of the coats is showing problems.

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Thank you everyone for the feedback

Single stage each layer of pigment deepens the color saturation. Light passes through and bounces back out. This is why different colors of primer give you a different hue of the final paint color. Sand off some and color will change unless you are really thick. You will get dark lines around the edges of the run as the pigment settles.
For a run you need something with zero flex so it only hits the high points. If a nibbler is possible I start with that and cut off some of the run then I use paper on a wood paint stick. I start with around 400 to knock down then get into finer grits for polish.
Now days I always use two stage as a home paint job is always going to have some issue to deal with so it is just easier to fix. Winds up being cheaper in the long run.
Good luck
ps the Mexico blue keeps calling me

Looks like your can was either not shaken, settled or there is some other issue like PPG sucks. I have sprayed hundreds of gallons of single stage paint. Everything from Dulux (google it I'm old LOL) Dupont single stage everything and have sanded and polished about a thousand cars as a guess. The one time I used PPG I applied a clear urethane over a base color and the clear pulled the pigment down in a run like that. Same result. Sad to see after 20+ years nothing has changed. Here are a couple cars with what I call "Developed" paint. I use a paint stick mostly with 1500-2000 then an MA with 3000 wet. Then three levels of pads before hand work.
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