Powder coating question

[maury]

I am new to powder coating, and have done several aluminum castings I've made for my Fairbanks "R".
There are some spots where I clearly didn't get enough powder on, and a few places where I over masked.
I'd like to correct these and get a better looking coat.

My question is, can I just clean and spray these areas, then bake again, or will baking a second time ruin the original coat?

Thanks for the help.
maury

[Kim]

I'm not an expert, but based on my limited experience, you can re-spray a part with a second coat, and it should work.  At least, that's the info I found online.  But the problem I have had with that is getting the powder to stick over the first coat.  I don't remember noticing a 'join line' between the new and old paint, but I did try to recoat the whole thing (not just the missed area), and just put more powder on the part that got missed the first time.

It worked OKish, but I just wasn't as pleased with the finish after the second coat.  I believe what I finally did was to strip more of the paint and then try it again. The second time (the second, second coat? ) worked better for me.  It may have been that I just wasn't getting a good ground on the part the first time around (the first second coat?).

But after that, I really worked hard to get better powder coverage.  The second coat business just hasn't worked well for me the few times I've tried it.

Kim

[maury]

Thanks, Kim. Ill try a part tomorrow. Do a little light sanding first. I think my ground is good, but, how can you tell if it isn't?
If the results are the same or not better I'll just live with what I have.

maury

[Kim]

Thanks, Kim. Ill try a part tomorrow. Do a little light sanding first. I think my ground is good, but, how can you tell if it isn't?

When I was doing some of my first parts, I used an ohm meter to check and make sure the part was connected to the grounding wire, but that was a lot of hastle and inferring it from the powder not sticking is much quicker and more effective for me.

If you don't have a good ground, the powder doesn't stick well, and you won't get good coverage. It looks the same as if you forget to turn on the voltage sources for the powder gun, or if the tip of the gun gets coated with powder.  All of those problems have the same symptom - the powder doesn't stick to the part.  So if it's not sticking, I check for each of these: Power switched on, good ground, clean electrode on powder gun. 

If the results are the same or not better I'll just live with what I have.

maury

Sounds reasonable to me!  That's exactly what I did.  It was better, but not as good as other parts, or as good as I'd have liked, but it was passable, and not worth stripping the part and doing it again. 

Good luck, Maury,
Kim

[maury]

Kim, well, I have second coated the part.
The color coverage is much improved, but like you said, the gloss is much reduced.

Thanks,
maury

[Kim]

Kim, well, I have second coated the part.
The color coverage is much improved, but like you said, the gloss is much reduced.

Thanks,
maury

Yeah, that's exactly what I experienced.  Not terrible, but just not as pretty as the single coated parts.  I tend to like that gentle gloss look of the powder coated parts.

Hope you are able to use those parts regardless. Stripping the powder coat is a chore unto itself! 
Kim

[maury]

Yup, I'll use the parts I have. The other choice is to throw them away and rebuild the engine with my iron castings which I have now. Then I can use paint.

Thanks for the help.
maury