Metallics.....2 Questions

K

Karibou

My project is a 2-tone job, white enamel on the top which I plan on clearing, and a very strong metallic blue bottom in DBC 2000. I have a couple of questions for the forums, one functional and one philosophical.

I've just started shooting the metallic on some smaller pieces and notice how tough it is to shoot smoothly. I've already had the metallics sag into some compound curves but been able to save it with some pre-clear sanding and re-basing. My main problem seems to be how unforgiving this paint is over body work. My body work is being done mostly in a homemade epoxy and 3M microballoons and this stuff is really tough to not pinhole. I've skimmed some of my bodywork with thinned epoxy resin, which helps, but the end result is that I'm having some minor ghosting problems even after 3 coats of DBC. I think the ghosting is texture based and not a "coverage" issue of the base. I plan with the remaining body work to skim the micro with extra resin to fill all the pinholes, but in the meantime I wonder if extra base might hide these ghost images? When I say pinholes too I mean subtle, these images are very very light.

My other question relates to design and look. After shooting some of this metallic I got to wondering if the vehicle will look weird with a non-metallic white over such a strongly metallic blue bottom. Does anybody here have an opinion on this? I've changed this project part way through as my original plan was to shoot a 2-tone white/gray with both being non-metallic enamels by PPG. Sorry for the length and thanks for your insights.
 
I'm curious about what seems to be an aversion to conventional polyester putties for final finishing. They are designed to help eliminate just the sorts of problems you seem to be experiencing. I do not see mentioned what primer(s) are being utilized, this can also effect the appearance of the job.

If you are getting "sags" in the basecoat, it is going on too wet, possibly due to one or more factors relating to gun adjustment or technique. DBC should not be particularly hard to spray, in my experience.

Color selection is all about personal preference. Most of the time I advise my customers wanting two-tone jobs to stick to an OEM color combo, as they have done the color research for you. At any rate, you will not be able to get meaningful responses to your color choices without posting photos.
 
My aversion to the polyesters sold to finish autos relates to theories circulating around the web that they have flex and adhesion issues. This work is going over very thin aluminum which has flex to it. I realize that these newer poly fillers are very good, but the metal can even oil-can in and out during operation and I wanted to get the best adhesion possible.

Another reason for trying to stay with epoxy is that I'm using SPI epoxy primer for the most part, although with the part I'm referring to here I did cover the epoxy filler with SPI regular 2k. There's been mention on these boards and elsewhere about adhesion in between the boundary of polyesters and epoxies not being the best, so I thought sticking with an epoxy based filler made the most sense. I'm using 2k primer in most areas instead of an purely epoxy based primer job so maybe my benefit is lost there with regard to the filler. Most of my primer work has been pretty standard as recommended here: SPI epoxy primer over bare metal, then the body filler, 2k then a sealer coat of epoxy. All my primers are SPI. I suspect my final sealer coats of epoxy may be too thin as I'm almost putting them on dry. I'm trying to keep my total paint weight reasonable as this is going on an airplane, so taking the "Perfect Paint Job" methodology but cutting the number of coats down.

Essentially my paint scheme is as depicted here, but with the blue being a bit darker and very metallic. The white is plain enamel, no pearls or metallics. I just thought someone here would have a reaction to the contrast between the 2 paints.

2003Gallery8.jpg
 
Oh, aircraft! I thought you were talking about a car or truck. lol. I don't think I am qualified to advise on that, although I do not think filling pinholes with poly putty would be a problem in any case.

Putting the epoxy on dry can cause all kinds of grief, not limited to adhesion failure. If you really need thin film build, reduction would be a better course than dry spraying.

I thought we had an A&P mechanic on the forum, but I can't remember who it was. Barry knows a few things about aircraft, though. I'm sure someone will come and give you more aircraft specific advice.
 
[QUOTE='68 Coronet R/T;11169]Correct me if I am wrong but aren't there standards regulations for aircraft paint?[/QUOTE]

Not for experimentals.
 
Talked to Barry at length today. Seems my sealer coats are too dry. Just resealed some parts with a much heavier coat and they look better. Also I was doing the 1:1:1 reduction on the epoxy and then misting it on with just 1 coat, which just isn't enough. When I do that reduction now with epoxy I'll do 2 coats as a final sealer to fill the scratches and cover the body work.

It's really true that the metallic base coats exploit any roughness or imperfection in the final coat of primer.
 
Texture irregularities and scratches show more with metalics for sure. I'd like to hear more about your epoxy/micro sphere filler. It's untrue-what you've read about polyesters not bonding well to epoxy primer (SPI)- from the testing I've done I've found the bond strength is higher than the strength of the polyester. Your choice to use an epoxy filler instead of poly for the better flexibility is probably a good move if these panels are flapping around alot. White over blue metalic-I remember Chevrolet having a two tone like this on the full sized blazer in the late 80's-early 90's and I always thought it looked great but they used a medium blue metalic. Your work should last for many many years considering the products being used.
 
Bob I think I just saw a truck with that paint scheme. It looks nice, but the blue is different as you said. Regarding the "micro," the body filler you make, I'll defer to an excellent article written a couple of years ago by a guy named George Sychrovsky about what to look for:
http://photos.imageevent.com/qdf_fi...ionarticles/Finishing a composit airplane.pdf

Hopefully the link works here in the forum. If not I can email it to you. This stuff seems superior to polyester fillers in every way except for one, which is spreadability and smoothness.

I shot some more metallics over the weekend with some additional guidance from Barry they really look great.
 
Karibou, I'll bet that epoxy filler is a lot tougher and more flexible but I wonder how it compares for heat related expansion. I know the glass reinforced polyester fillers seem to expand more than regular polyester fillers-maybe because the glass conducts heat more. I might have to do some testing.
 
I've used micro balloons extensively when I worked as an A&P doing all kinds of fiberglass/aramid/carbon fiber repair. I did mix a lot into epoxy resin for potting repairs to fill damaged honeycomb core. Interesting way to make a light epoxy based surfacer. I can see in my experience where you could make the mixture too dry, with a lot of balloons, but it looks like the write-up gives you good guidance.

One thing I didn't see was a warning not to breath Micro balloons. This stuff is very bad for your lungs and floats around like fine dust.
 
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Mustang408;11390 said:
One thing I didn't see was a warning not to breath Micro balloons. This stuff is very bad for your lungs and floats around like fine dust.
Click to expand...

Absolutely. This stuff qualifies as nanotechnology and as such it has properties and side-effects that are mostly overlooked related to health. That article just shows him wearing a dust mask, but I wear a respirator and always stir the balloons into the resin very gently. If you stir hard you get an affect like powdered-sugar mixed with helium: the stuff goes everywhere and just hangs in the air. It can't be good for you.

The toughness of this stuff is amazing, but I'll tell you that trying to sand it over a thin aluminum skin is a real job. I've taken to adding more layers of SPI epoxy primer underneath the repair to give me more time before a sand-through to bare aluminum, plus I may try Shine's technique of using tape over high spots as a means of protecting the surrounding area while sanding.
 
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