First time painting, running into a couple problems

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PostPosted: Mon Aug 17, 2015 10:11 pm
Hello and thanks in advanced for your time.

I'm painting a front bumper cover, but just realized a couple problems I might have while doing the prep work. I have other touch up jobs I plan on doing, but I'm getting my practice on the bumper cover.

The bumper cover is a plastic OEM primed bumper cover.

I scuffed the bumper using a gray scotch bright pad (initially I started lightly scuffing it with a 400 grit sandpaper but I thought the scrapes may be a little too deep).
I just looked at the "What Grit to Use" sticky and it said 400-600 grit. I do have 600 and a red scotch bright as well. I'm not sure what grit the gray scotch bright translates to, but several people have told me the scotch bright is preferred over sandpaper for scuffing.

I bough a 4 piece gravity fed spray gun kit with 2 1000 ml guns and 1 100 ml detail gun.
One problem I just realized while getting acclimated to the guns was my air compressor probably isn't up to snuff. I have a larger pancake compressor (it's got more hp than your typical pancake compressor). It seems to hold a continuous 30 psi just fine for the small 100 ml gun even when the compressor kicks on, but the pressure goes down if I'm using the 1000 ml guns.

1. Would it be practical to paint the whole bumper cover using a 100 ml gun?
2. Is there any cheap paint with a similar viscosity that I can use to practice spraying before I use my automotive paint?
3. Also, what's the typical shelf life of the paint / clear coat?


I bout the paint and primer a week ago, and I wanted to get this job done this week, but if I'm waiting on a better compressor I may have to postpone it. The paint is a 2 part (paint and reducer) metallic paint. The paint, reducer, clear coat and hardener are all factory sealed and the only one that has been cracked open and resealed is the paint.

Thanks

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PostPosted: Tue Aug 18, 2015 8:59 am
welcome.

Sure you can paint a bumper with a smaller gun, especially if a solid color. If metallic in the paint you have to be a little more careful to avoid striping, unevenness, etc.

You can practice with lacquer thinner but it will not be the same viscosity as paint or clear coat. I really can't think of a material to put through it other than the real stuff, if you want to practice.

Shelf life for paints, reducers, activators, etc. is measured in years not months - if kept sealed and in a cool area. If you keep paints out in a shed where it gets to 120F in summer and -20F in winter, then shelf life is a few days if you are lucky.

Scotch pad grit table:

download/file.php?id=2001&mode=view



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PostPosted: Tue Aug 18, 2015 10:44 am
Thanks a lot for the help!

So to avoid striping etc. I want o do a 50% overlap and cross coat, are there other techniques I should try? If I do get striping I can always put on another coat to even it out right? One other thing I noticed with my compressor is the moisture that comes out. Is this a real problem? Would adding a water trap be worth it?

That's good to know about paint shelf life, I've been keeping them sealed indoors. I'm assuming with the metallic paint it can settle a bit more than other paints, just needs to be shaken up well.

I used the dark gray (ultra fine) so it looks like that's around a 600 grit equivalent.

The guns I have are 1.0mm 1.4mm and 1.7mm. With the metallic paint and clear coat should the 1.0mm gun be a problem?

One more question, they gave me some strainers when I bought the paint/clear-coat. What do and don't I want to strain when mixing it together (the base-coat, reducer, clear-coat, hardener).

Thanks for putting up with all my questions, I'm a very thorough person.

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PostPosted: Tue Aug 18, 2015 12:11 pm
To even it out, if shooting base coat (not single stage) - you can pull the gun away a few inches and randomize your spray pattern on your last pass, or extra pass of color. This is called a "drop coat"; I'm not a huge fan of it but if done while the prior coat is still flashing off, it's ok. Keeping the gun exactly parallel to the panel goes a long way to avoid metallic striping -- if you tilt the gun you can easily get uneven metallic deposition - stripes.

You need to remove moisture, it'll ruin your paint job. Do no proceed unless you have clean air, and enough of it.

1.4 is a decent general purpose tip size.

Mix your materials in a mixing cup, then pour through the strainer into your gun's cup. If your gun has a small filter inside of the cup near the bottom -- get rid of that it's a sick joke gun companies play on us and will just clog up and ruin your day.



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PostPosted: Tue Aug 18, 2015 1:15 pm
chris wrote:To even it out, if shooting base coat (not single stage) - you can pull the gun away a few inches and randomize your spray pattern on your last pass, or extra pass of color. This is called a "drop coat"; I'm not a huge fan of it but if done while the prior coat is still flashing off, it's ok. Keeping the gun exactly parallel to the panel goes a long way to avoid metallic striping -- if you tilt the gun you can easily get uneven metallic deposition - stripes.
You need to remove moisture, it'll ruin your paint job. Do no proceed unless you have clean air, and enough of it.


Thanks, I think I'll put the painting part on hold a few weeks until I can get the proper air equipment. I have a friend that has a 2nd pancake compressor that he uses to combine together. As long as I put it on different circuit breakers I think that should give me enough CFM. Wanted to get it done this weekend (4 day weekend for me), but I think I'll wait so I can do it right the first time. Would I want to put the base coat paint in a shaker after sitting for about a month or is shaking/mixing by hand enough?

1.4 is a decent general purpose tip size.

Mix your materials in a mixing cup, then pour through the strainer into your gun's cup. If your gun has a small filter inside of the cup near the bottom -- get rid of that it's a sick joke gun companies play on us and will just clog up and ruin your day.


Good to know, I don't think the has any filters in it.

With regards to the flash drying. Do subsequent coats have to be put on while the previous coat is "flash dried" but not completely dried? What happens if there is a long time (like 24 hours) between coats? Does this have to do with adhesion?

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PostPosted: Tue Aug 18, 2015 1:29 pm
shaking it via machine is not a bad idea, if easy enough.

read your tech sheet for the paint, it'll specify recoat times.

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