Paint Question on AMT 63 Vette

[Len Woodruff]

I am having trouble with this paint mostly on the left rear deck.

I am using Scale Finishes with a urethane 3 part clear. I have never have had problems putting Urethane over any Scale Finishes base coat.

I let the primer dry a day. Then shot the color. Waited an hour and shot the clear.

Thanks in advance for your help.

 

 

[espo]

Looks like surface scratches on the body under the paint. Think about any- body prep prior to the color coat of paint.  

[Len Woodruff]

1 minute ago, espo said:

Looks like surface scratches on the body under the paint. Think about any- body prep prior to the color coat of paint.  

No sanding done on the body. Primer was fine and so was the color coat. The problem showed up when the clear was put on.

[espo]

2 minutes ago, Len Woodruff said:

No sanding done on the body. Primer was fine and so was the color coat. The problem showed up when the clear was put on.

Was the primer coat sanded before the color coat? This is just what it looks like to me. 

[Classicgas]

That's a tricky one. I agree with David, looks like sanding scratches that have ghosted. It doesn't look like lifting or crazing. If no sanding of any sort was done it's a mystery to me.

[Ace-Garageguy]

IF (big if) no sanding was done to either the body or the primer, the ONLY thing it can be is "flow lines" from the molding process being attacked by the solvents in the clear.

I've seen similar effects over the years.

During the molding process, uneven mold filling can result in eddying and lines from the flow "stuttering" if the injection shot falters for any reason, or if the mold isn't evenly heated.

This can result in artifacts in the molded part kinda like tide-lines on a beach, but often invisible to the naked eye until something with a solvent hot enough to aggravate them is applied. The material within the lines is not uniformly hard, so solvent soaks into softer areas.

Local poor solvent resistance is also more of a problem these days with the increasingly cost-engineered styrene that offshore manufacturers seem to be using.

I would tend to think the best fix is to strip it, then shoot the body with a catalyzed primer that has better "hold out" than what you used previously...though I've been able to "hold down" ghosting with successive coats of automotive primer-surfacer, sanded in between.

This is a somewhat similar problem for illustration.

The light areas were swelling that occured AFTER the hood peak, an emblem, and some sink marks were sanded out. The work cut through the uniformly hard surface, exposing a softer under-layer...which swelled when lacquer primer hit it.

Fortunately, the problem did show up just after the first primer coat, and I was able to kill it prior to color...using essentially the same procedure (as above) I relied on to deal with real-car substrate-swelling back in the lacquer days.

Final hot metallic Duplicolor, with zero trace of the disturbed surface showing through.

 

Some kind of sealer might also work, but in general, I try to stay away from them.

 

Edited November 25, 2023 by Ace-Garageguy

[Len Woodruff]

Thanks guys. This is the an old AMT prestige kit with white plastic. My guess it was molded before they sent any of the kits to china.

I used Dupli-Color Sealer #1699 on the body.

This is the second paint job on the car using the same process except on the 1st paint I used the Dupli-Color 1K clear that I decanted.

[StevenGuthmiller]

I've had almost exactly the same thing happen in the past when I tried sanding out some boogers from the paint and then clear coated over it.

Depending on the clear, the sanded area can "ghost" and although it may look fine prior to clear coating, it becomes greatly amplified and very obvious once the clear is applied.

This is part of the reason why I never sand the final color coat prior to clear coat.

If sanding is required to eliminate junk, I'll shoot it with another coat of color before clear coating.

Granted, I'm using nothing but automotive lacquers for everything, so the hot nature of the paint and clear is of course a factor.

 

That said, whether or not his is the issue with your model, I have no idea, but it sure looks like it.

 

 

 

 

Steve

[NOBLNG]

I gotta say those are scratches of some kind. They seem to cross over each other in spots.

 

Edited November 25, 2023 by NOBLNG

[Len Woodruff]

I did use a scotch bright pad to clean the 1st round of color/clear. But I have done this with many bodies and never had this show up on the repaint.

I am stripping the body now. 

I will reprime it with the Dupli-Color 2n1 that will fill the scratches then put the sealer over it.

[Pierre_tec]

If you said Scotch brite! You find your problem then

I use it to “kill” the shine on a new body, before primer, the maroon that I believe is 400. Beside that is too aggressive, try using light mist of flat black as a guide coat to check for any sanding marks before paint. Clear is a big magnifying glass

try lightly sand until 1.5k that area and repeat, should be fine

[Len Woodruff]

12 minutes ago, Pierre_tec said:

If you said Scotch brite! You find your problem then

I use it to “kill” the shine on a new body, before primer, the maroon that I believe is 400. Beside that is too aggressive, try using light mist of flat black as a guide coat to check for any sanding marks before paint. Clear is a big magnifying glass

try lightly sand until 1.5k that area and repeat, should be fine

I use the green Scotch Bright

I have stripped and repainted many bodies over the years using the Scotch Bright to remove the paint & primer with perfect results.

One other note is that the Hood & Hard Top turned out fine using the same process as the body. That would eliminate the plastic being a problem?

 

[bobss396]

It looks like what 1:1 car painters call "solvent shot". Likely too heavy a hand with the clear and/or too soon after the color coat. I have done it recently with Duplicolor paint and SEM 1K clear,

[Ace-Garageguy]

28 minutes ago, Len Woodruff said:

One other note is that the Hood & Hard Top turned out fine using the same process as the body. That would eliminate the plastic being a problem?

Not necessarily. "Flow lines" showing up from uneven mold-filling during the injection process may only show on one part in the entire kit, or may not occur at all on the same part made at a different time.

That said, the magnified image does indeed appear to be the result of some kind of paint-surface disturbance, not a problem with the plastic itself.

Edited November 26, 2023 by Ace-Garageguy

[Len Woodruff]

9 minutes ago, Ace-Garageguy said:

Not necessarily. "Flow lines" showing up from uneven mold-filling during the injection process may only show on one part in the entire kit, or may not occur at all on the same part made at a different time.

That said, the magnified image does indeed appear to be the result of some kind of paint-surface disturbance, not a problem with the plastic itself.

I tend to agree with you Bill. Not sure how to keep it from happening agin though?

[NOBLNG]

17 minutes ago, Len Woodruff said:

I tend to agree with you Bill. Not sure how to keep it from happening agin though?

Get some good quality sanding pads? Scotch Brite is for scrubbing pots and pans.?JMO.

[Ace-Garageguy]

46 minutes ago, Len Woodruff said:

I tend to agree with you Bill. Not sure how to keep it from happening agin though?

I think stripping, re-primering, and repainting is the hot setup.

HOWEVER...I personally wouldn't use the "2n1" primer, as it tends to obliterate fine surface details like emblems and scripts.

The standard "sandable" primers will fill 400 grit scratches easily, without too much film build.

Sealer over that is an option, but I have zero experience with Duplicolor sealer/primer. Some guys swear by it, though.

Far as the Scotch-Brite pads go, though they're widely used in the real-car refinish biz, I find they have drawbacks for model work.

The big bugaboo is that they don't get into model-sized crevices or details.

I also think the gray is a better choice for model work, if you insist on using them, than the red.

The best bare-plastic surface prep I've found after considerable experimentation, is a hot-water scrub with something like Comet and a toothbrush.

Not only does it scuff the surface uniformly without scratching it, gets into all the tiny areas (like next to emblems) that scuffing-pads or sanding-pads just ride over, and it also removes any "mold release" or other possible contaminants from the manufacturing process.

I always follow that with a last-minute wipedown with 70% isopropyl just prior to paint, using clean white paper towels, as it will virtually eliminate the possibility of "fisheyes" if done carefully.

EDIT: I started doing the iso wipe while painting real aircraft, where a fisheyed fuselage side or wing can cost literally thousands of dollars in labor and material to correct.

 

Edited November 26, 2023 by Ace-Garageguy

[Ace-Garageguy]

18 minutes ago, NOBLNG said:

Get some good quality sanding pads? Scotch Brite is for scrubbing pots and pans.?JMO.

It's used extensively in the real-car refinish biz.

[Len Woodruff]

Thanks Bill.