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Old 09-14-2018, 01:45 PM   #1
Mike's money pit
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Painting plastic parts

My son has a 2004 Toyota pick up truck. I hope it’s OK to ask my question here. I have enjoyed reading in this part of the forum and know that there are some experts here. I am trying to repaint one of his fender flares. The paint that was on the fender flare had chipped up. I sanded the flare smooth with 220 grit sandpaper. I didn’t get it as smooth as I thought because you could still see some of the chipped looking areas through the primer. However, after spraying on the primer, it wrinkled up in the same areas after just a couple of minutes. I was using rattle can primer called “scratch wizard” that has paint matched for his truck. I used their paint prep and degreaser solution on the part before priming. I am sure I will have to sand this off. The worst of the bubbles are in the same place that it originally chipped up. Thanks for any advice.
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Old 09-14-2018, 01:49 PM   #2
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Re: Painting plastic parts

This is the paint I am using. I had decent results painting a replacement door handle on the truck with it.
Thanks again,
Mike
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Old 09-14-2018, 10:52 PM   #3
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Re: Painting plastic parts

Rattle can repairs will have you chasing coating failures, to be frankly honest. I have compassion for wanting to help your son but this repair is not going to happen with satisfaction for few dollars.

Take it to the proffesionals and pay them to do it right.

Please remember that there's no such thing as good cheap paint.
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Old 09-15-2018, 11:53 AM   #4
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Re: Painting plastic parts

Too many variables to pinpoint the exact cause here, but if you want to try again using what you already have, sand and scuff it back to tight paint, make absolutely sure it's clean, and start priming with very light coats. Go super light on your passes (as in almost dry) and let it totally flash off between coats.
A neat trick with rattle can paints is to first heat the paint in the can with a heat gun or really hot water. Heat usually loosens up the paint making it more fluid and also increases can pressure to some degree, thus creating a finer spray.
The idea here is to prevent wet solvents from heavy coats from penetrating previous coats and lifting. If you successfully build a base of primer and color without any lifting, you might get lucky and get your clear coat on without issue.
It's worth a shot, anyway.

Last edited by oem4me; 09-16-2018 at 12:51 AM.
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Old 09-15-2018, 12:03 PM   #5
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Re: Painting plastic parts

Thank you both for taking the time to respond. I wish I had a picture of the fender flare before I started on it. The wrinkled primer was in the same place where the paint originally failed and so I assumed it was contamination on the fender flare. I did put a much heavier coat on the part that failed. I was trying to fill in some minor imperfections. I will sand it back down and give it a shot with thinner coats. Thanks again.
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Old 09-16-2018, 11:03 AM   #6
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Re: Painting plastic parts

It isn't a "contamination" issue, that word is WAY WAY overused when talking about paint. What is happening is the primers solvent is getting under the super thin layer of paint and lifting it up so it wrinkles off the primer that is under it.

Think of it as a sheet of Saran Wrap over it, but it has some little cuts in it. If you poured something over it that liquid is going to get under it, that is what is happening with the sanded thin and cracked paint.



As said, very dry coats of primer to build up a layer of protection is the only way you can solve it. And then there is still no guarantee that when you paint the color and clear over it that the solvents aren't going to go through the primer and do it all over again! And when I say "very dry coats" of primer, I am saying CRAZY OVER THE TOP DRY COATS. Dusting them on and walking away to leave it fully flash off before you dust another coat over. VERY THIN coats, "TOO THIN" if you know what I mean.

But when you build up that layer of primer you are increasing the protection so you can't loose. Just built it up a lot, scuff it so you don't sand it thin again, and then apply the color and clear lighter than you would have so the solvents don't soak through.

1k products like those are pretty hard to work with when you have flaws like this.

Brian
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Old 09-18-2018, 06:37 PM   #7
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Re: Painting plastic parts

Update:
I took my time and did very light coats of the primer after sanding everything back off. The primer laid down nice and smooth. I have wet sanded it with 600 grit and have let it dry. My plan is to wipe it down with wax and grease remover and then start spraying light coats of red. I am figuring on quite a few coats and letting it flash off about five minutes between each one. Then I figure I will clearcoat it five minutes after the last coat of red. I am planning to do light coats of clear also. Does this all sound correct?
Thanks for all the help,
Mike
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Old 09-18-2018, 08:11 PM   #8
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Re: Painting plastic parts

Quote:
Originally Posted by Mike's money pit View Post
Update:
I took my time and did very light coats of the primer after sanding everything back off. The primer laid down nice and smooth. I have wet sanded it with 600 grit and have let it dry. My plan is to wipe it down with wax and grease remover and then start spraying light coats of red. I am figuring on quite a few coats and letting it flash off about five minutes between each one. Then I figure I will clearcoat it five minutes after the last coat of red. I am planning to do light coats of clear also. Does this all sound correct?
Thanks for all the help,
Mike
Sure, but flash time is one of the most important, let it "dry" flashing off the solvent good before applying the next product or even between coats.

Understand, this is only needed when you KNOW you have an issue with a substrate. But keeping solvent from soaking in is what you are after and that falls into many different things.

If you weren't using aerosol cans but mixing paint and spraying it.

1. The amount of reducer you put in the product (primer, paint, clear, what ever)

2. The "speed" of the reducer or "temp" that it's for, the higher the temp, the slower it flashes.

Now, with aerosol or spray gun.

3. The temp of the item you are spraying, the colder it is the slower the solvent flashes.

4. How heavy you apply it, slow gun or can travel, a lot of overlap, all that can trap solvents.

5. The flash time between coats.

ALL these things affect how the solvent flashes off. Knowing this, and controlling it throughout just adds to a better finished product.

Brian
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Old 09-18-2018, 09:40 PM   #9
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Re: Painting plastic parts

No need for wax and grease remover at this stage, unless you've introduced wax or grease. A tack rag is all you should consider using because adding yet another chemical will potentially harm your result.
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Old 09-18-2018, 10:04 PM   #10
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Re: Painting plastic parts

Quote:
Originally Posted by Mike's money pit View Post
Update:
I took my time and did very light coats of the primer after sanding everything back off. The primer laid down nice and smooth. I have wet sanded it with 600 grit and have let it dry. My plan is to wipe it down with wax and grease remover and then start spraying light coats of red. I am figuring on quite a few coats and letting it flash off about five minutes between each one. Then I figure I will clearcoat it five minutes after the last coat of red. I am planning to do light coats of clear also. Does this all sound correct?
Thanks for all the help,
Mike
Yep, sounds like a plan. As long as things are going smoothly, lightly scuff with a scotch pad (not sand paper) between coats only if needed. Keep those film thicknesses to a maximum. If you get good prime coats and color coats on there without issue, chances are a few light coats of clear and one final wet coat will seal the deal. Done.
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Old 09-19-2018, 11:01 AM   #11
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Re: Painting plastic parts

Thank you guys very much for all the advice on the fender flare. I put the color on and cleared it last night. I took it out and put it in the sun this morning to help the paint harden. It is not perfect, but it looks so much better than it did. I’m not sure if I will try to lightly buff off the orange peel. I figure I’ll put it on the truck first and see how it matches up.
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