1st post - Need help prepping/spraying bc/cc on door

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PostPosted: Tue Jul 17, 2012 3:28 pm
Hello!

First post here, looking for some advice.

I have never painted with an automotive gun before, although I have done a fair amount of body work (cab corners on trucks, patch panels, etc) with very good results. I have to paint a replacement door for one of my trucks, and I want to get it right the first time. I've been reading a lot about painting, and I'd like to finally start doing it. Here's what I've got:

The vehicle is an Isuzu NPR (commercial cab-over truck). The door is from a donor vehicle, same color as my truck (white) and in fairly decent shape, although someone painted a part of the door with a brush to cover a company logo. I don't know what kind of paint was brushed, on, but I confirmed with a factory rep that the truck was painted with bc/cc.

For prep so far, I peeled off the stick-on logo that was painted over, washed the door completely, removed most of the accessories (will tape the rest), and rubbed it down with wax and grease remover. I plan to clean it with glass cleaner right before I start sanding. The factory paint is in pretty good shape, i.e. no rust, major scratches, etc. I plan on sanding the brushed on paint with a DA disc sander w/220 grit until the brushed on paint is removed, then block sanding the whole door with 320 grit.

After that, I will shoot the primer/sealer, let dry for 3 hours or so, then shoot the base coat, then clear coat, per the instructions on the can.

I'm using all Dupont paint supplies purchased from a local automotive paint supplier, and a Harbor Freight "purple" HVLP gun with a 1.4mm nozzle and 20oz cup. The gun is brand new, and I just thoroughly cleaned it with lacquer thinner. I plan on "tuning" the gun before I used it per the instructions under the "atomization" section.


Questions:

I'm aware that most people use a different gun for priming and painting, but at this point, all I have is 1 gun. The counter guy at the paint store said that I can get away with it as long as I disassemble and thoroughly clean the gun immediately after use. Is this the case, or should I just spend the $40 and buy another HF gun for priming?

What pressure should I have at the gun? It has it's own regulator, and the manual says that min pressure is 15, and max is 45.

I have enough material to practice a bit before I shoot the door. Should I practice with the base coat, or the clear coat, and what's the best surface to practice on?

How many coats of base should I shoot, how many clear, and what's the dry time between coats?

As an aside, I own several classic cars, some nice, some are work in progress. I've always wanted to learn how to paint, but I wanted to start on a vehicle where the cost of mistakes are fairly low, so this is why I'm painting this door.

Any other words of advice/watch-outs/admonishments, etc. for a first time painter?

Thanks...

Chris
Monroe, CT

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PostPosted: Tue Jul 17, 2012 4:02 pm
Hey Chris.

Some answers, and you obviously read a lot here and did your homework...great!

1. You don't need a separate gun and a 1.4 tip is a great 'general purpose' tip size so unless shooting a real heavy primer you should be fine. Check the tech sheet on the primer to be sure.

2. Start the gun out around 30 and up the pressure if you have having issues with texture/orange peel.

3. You will find base is easier to shoot than clear so if you only have one thing to practice, I'd pick practicing with the clear. Both would be better of course. Write down all your gun settings, room temperature, speed of activator/reducer used, gun distance from panel, etc. Keep track of as many variables as possible, so you can repeat what worked well for you.

4. Shoot light/dry coats of base...if you start to get lingering gloss that doesn't flash away quickly you are putting your base on too wet. Two coats minimum but with white you will probably need three. You want to have great lighting and check for hiding/coverage.

5. Two coats minimum on clear...three if you expect to sand/buff the clear after you are done...so I'd say "three" for sure on your first project.

6. Check tech sheets for flash time between coats and re-coat window. On the clear, check with your finger on part of your masked-off spot and if you can pull your finger away without 'strings' of clear bridging between your finger and the masking...you are ok for recoating.

-Chris



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PostPosted: Fri Jul 27, 2012 11:30 am
Update/Questions:

Ok, I was a bit nervous about shooting paint for the first time ever on a door I was going to use, so I decided to practice on a fridge door that I had laying around (one of the benefits of owning a junk removal company). I bought some left over bc/cc dupont bc/cc paint at the same paint supply store to practice with. I wiped the door down with Prep, sanded it with 220 using a 6" da sander, then wet sanded it with 320 until I had a uniform dull finish on the door. I then shot the door with the epoxy primer/sealer, Dupont 2510S, cut 2:1 with Dupont 2505S activator using a 1.4 tip at 35lbs at the gun inlet (recommended was 30 - 40)

I'd done my best to tune my gun before I shot anything. I set the pattern using laquer thinner on a coated cardboard sheet, and ended up with about an 8" long cigar shaped spray pattern that was about 1 1/2" wide. I could hold the trigger for about 1 1/2 seconds with no drip. For material feed, I opened the valve 3 half turns from tighly closed.

I had no real feel for how the gun would lay down the paint, so my first few passes were too light in that I could see the nasty brown fridge color through the primer, and it was incredibly orange-peely. I slowed the gun WAY down so that the gun could apply a thicker coat, and it seemed to work well. I got much better results, a basically smooth, shiny finish with very little in the way of orange peel.

Unfortunately, my application was inconsistent. Parts of the door are as I mentioned...smooth, etc, while parts have heavy orange peel. So...

Should I (or can you) wet sand the epoxy primer-surfacer before laying down a base coat?

Recommended primer flash time is 30 mins. I'm already past that. Will it make any difference at all if I wait until the weekend to shoot the color and clear?

If so, what will I have to do to prep the primer/surfacer?

Does my gun tuning sound right? If not, what should I change? - Using the HF "Purple" gun.

This is tough going for me because I have absolutely no experience shooting paint, so I really don't know what to do to remedy/improve my paint application technique.

I'd appreciate any help at all.

Thanks...

Chris

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PostPosted: Fri Jul 27, 2012 3:22 pm
I'm not very familiar with that gun, but based on what you said, it sounds like you have it dialed in pretty well.

Yes, you can wetsand that epoxy -- and you really need to do that to get it flat before you go to color. The flash time is the minimum time before recoating. In fact, if you shoot color/clear too soon after shooting epoxy (or other primer) you can get gloss die-back, so it's always safer to let this stuff cure longer before shooting color.

If you let the epoxy cure for a day or two, then wetsand it with 400 (or 600 if shooting a metallic color), you will be good. Clean it off real well after sanding, wax/grease remover, tack cloth -- the usual drill.

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