I went in to Keystone today and put an order together for paint and supplies for the '72. The paint guy seemed rather impressed with the recommendations in the Corvette Body & Paint Repair Basics Tech Tip. He hooked me up with pretty much the exact stuff in there, but when I told him I was painting black, he said I could just as well go with black K36, and he recommended that instead of two color coats and three clear coats, I use a single stage color so I could MIX the middle coat half clear half color. That way I could paint continually without waiting for dry, and it would eliminate almost all dust under the clear coat. What do you guys think? Anyone tried this?

-=Boston!=-

 

I did 2coats black and tree coats clear -everyone I talked to said thinner is better-mine looks like a black mirror. But I spent along time preping the surface ,I mean months

 

Prep is everything.

I've never heard of mixing the clear with the base coat, but I'll find out tomorrow. That don't sound right but....

 

That might work fine for a regular body shop job, but if you want a top notch finish, you'll have to color sand & polish anyway. If you're doing it at home you're going to have some dust in the finish until you polish. Even if you have a booth to eliminate the dust, unless you're really good with the gun, you'll have some amount of orange peel that will need to be cut down & polished. I've always done base / clear as seperate stages.

 

IT seems with a black simi opac finish ( is what a mix would be )Black on clear On black woul not be of any benefit. black is black unless your talking some sort of ghost flames- they would be silver or gray or some other color anyway.

 

Just a couple of thoughts on what you were told.... I think that was probably my tech paper you were using when shopping for materials...

K36 does, in fact, come in several colors, including black. Your paint guy's recommendation to skip the basecoat and just use the black K36 as the base under the clear is based on 2 things: First, that thinner is better for paint durability, and second that is will reduce costs by about $300 - not bad..

The reasons I would not recommend doing this are several:

First, when you're shooting and sanding the K36, you're using it as a sanding base & filler. During the blocking process, it's important to be able to really tell where you're sanding and what progress you're making. I have found that this detailed sanding process is visually much easier if you use a lighter primer. The black primer is difficult to critically evaluate while you're sanding.

Second, during your final 600-grit wet sanding process just prior to paint, you will cut through the primer in several areas. As you cut through the layers of black K36, there will be a barely noticeable "ring" around the cut areas. These will show up as imperfections once you lay the clear on top of it. Also, the K36 is intended as a "high build" primer, so you cannot "touch up" the sand-throughs without a significant K36 build-up for the touchup. This will show up under your clearcoat.

Finally, the black color of the K36 is not as "dense," or "deep", as the black basecoat: the K36 is tinted black without the intent of it being a true solid color. The black basecoat is an incredibly solid and deep black that is not duplicated by the tinted fill primer.

All that being said, I would not use the black K36 at all: When your primer is the same color as your basecoat, it is very difficult to see where you're painting during the first coat application. This makes it difficult to evenly control film thickness. I suggest you use the standard light grey K36, do all your sanding (you're going to be sanding almost all of it off anyway, so film buildup is not a concern), and then shoot a "real" black basecoat over the light grey fill primer (you don't need to shoot a sealer over the K36 unless you have a LOT of sand-throughs - just shoot some DP sealer or some 50% reduced K36 on the sand-through areas very lightly). Shooting black base over the grey K36 will allow you to really see your progress and control your deposit thickness. The black has amazing dense coverage, so you can shoot a light tack coat and two near-wet coats for a total, intense black coverage.

Dust is not a problem: Between basecoats, let the base tack up and nearly dry (30 minutes). You can then use a piece of Scotchbrite to knock out any "nubbers" in the coat you just applied. Do a light tack-cloth wipe-down after using the Scotchbrite, and shoot the next coat. Do not use the Scotchbrite on the last basecoat prior to clear. Blow the clear on it after letting the last basecoat set up for 30 minutes - apply 3 coats. Any nubbers you get in the clear can be wetsanded and buffed out.

The problem with mixing base in with the clearcoat is that the basecoat is not a stable pigment: It needs the clearcoat to protect it from oxidation and UV breakdown. When you mix base with the clear, you end up with pigment exposed to the oxidizing elements at the surface, and the surface finish of your paint will eventually turn slightly "hazy." None of the paint manufacturers recommend doing this, even though I see people doing it all the time for whatever reason. I really recommend you just shoot clear over your solid black basecoat - the car will come out looking like a mirror that's a foot deep.

Although some of these recommendations are my own opinions based on the techniques that I like to use, most of this is the way the manufacturers recommend using these products. I've been shooting cars for 25 years, and I'm certified by PPG, Dupont, and Standox. If you stick to the "normal" process you will not be disappointed.

 

Thanks for all the thought you guys put into this! Lars, your explanation for not using black primer makes sense. The reasoning the paint guy gave me is simply that chips in the base wouldn't show up nearly as much with black primer underneath. I do see what you mean about being able to tell where you're working, though.

I didn't explain myself well regarding the color though: he suggested that I do all the prep work, THEN shoot two coats of black base, then immediately one coat of base and clear mixed, then two coats of straight up clear. He said since I would be using DBC single stage paint (that will mix with clear unlike DBU), I could shoot all the coats without waiting for them to thoroughly dry, cutting down on time exposed to dust in my garage. It was a technique he said he learned only after he'd been dissapointed by the dust under the clear on the last black show car he painted.

Thanks for all the tips, Lars; it indeed was your article I brought with me with everything I would need highlighted right in the text!

-=Boston!=-

 

Anyone tried this method?

 

One thing, the PPG P sheet information on K36 shows is when you tint K36 you have to add more hardener and the darkest tint takes something like twice the hardener so the 4-1 is now 4-2

Steve

 

I actually used that method but in a different way. I went with PPG Concept Urethane, and sprayed 3 coats of straight color. I then mixed the color 1:1 with DCD35 clear. Sprayed on another 3 coats...i could have sprayed on straight clear after this, but i realized i could have too much paint on the car, so i opted to leave it at that. I then cut and buffed the entire car, and it came out great, looking deep and slick. However, i paint everything in a very good booth.