Paint pinhole problem

W

wrndln

Well-known member
I started color sanding the trunk lid on my 28 coupe and discovered a problem. I am noticing some small pinhole looking spots on the lid. I am pretty sure there were no pinholes on the lid before painting it. I did have to use a little Rage Gold filler on the lid, which could have created pinholes. I could be wrong, but I am pretty sure there weren't any pinholes in the filler. Anyway, after color sanding the lid, except for the small pinhole looking spots, the lid finish turned out pretty good. I know I will need to repaint the lid, which is not a big problem, as I need to paint some other item anyway. I am wondering how to handle the very small spots. Should I just use a little two-part filler, like Evercoat Metal Glaze, for the very small holes and then reseal the lid (epoxy sealer) and repaint it. Is resealing necessary? My other question is: Is there anything else that could cause the small pinholes in the finish? I was very careful in using a wax and grease removal liquid and a tack rag before painting. Any suggestions?
Thanks for any help.
 
If it is just the paint that has the pinholes, it's probably a wax, grease or silicone contamination problem. In the old days they had "fisheye eliminator" that you would add a few drops of to the paint when you mixed it. With all these new paints I don't know what they do now. I'm sure someone out there will have an answer. Good luck.
 
Lots of small even pinholes can be "solvent boil".

Are you using same brand compatible paint and thinners?
 
I really need more info to help. The previous posts couild be correct, you could also have some issues where you have pinholes in the filler that are just appearing. Get a magnifying glass and find out how deep the holes are.
Are they only where the filler is?
Have you followed the min and max dry times on the tech sheets for all the products? Are you familiar with recoat windows?
 
I dont know about paint problems but if they are really pinholes through the metal, you might drill them out with a small 1/16, 1/8" drill to get to good metal and fill them with non-acidic solder with a propane torch.
 
WRNDLN--- The current issue of Auto Restorer magazine has an article by master restorer Larry Lyles that deals with your problem, among other things. Try him at lplbodyworks.com
 
A couple years ago I painted a horn with DP-90, then came back an hour later with DCC 9000 and I had some very small pinholes. The bodyman told me I probably didn't wait long enough for all the solvents to evaporate from the primer. I should have waited another hour or two before topcoating.
 
I am assuming you took the time to examine the surface prior to your final prep and these defects were not there before you applied your topcoat.

Very likely it is solvent pop that was caused by either using too cold of a thinner, or you got in a hurry and did not allow the paint to flash off between spraying the finish coats. Depending on the severity of the damage, you may be able to salvage what is there without a total repaint by lightly wet blocking the entire panel with 1000 grit paper. Wash the entire decklid with soap & water and blow dry with air immediately. Anywhere there is a pinhole put a small sliver of tape as a marker beside the damage so you can easily find it later. Mix a small amount of your paint with hardener but without any solvents, and using a toothpick dip it into the paint and insert one drop into the pinhole. After all holes have been filled with one drop, allow the piece to dry overnight. The next day, mix up another small amount of paint and repeat the process. Do this as many times (as many days) as it takes overfill the holes slightly where they kinda look like a "scab over a wound on your skin". Allow to thoroughly dry. Next, using a small hard flat surface as a backing to your 1000 grit, lightly hone the raised area of the added paint until it is flush with the surface of the surrounding areas. Again, ...a little goes a long way here. Once flat, wet blocksand the entire panel again and then buff. As long as the paint does not have metallics or is not BC/CC, it will likely be undetectable.

.
 
Brent,
Thanks for the information on how to try to repair the problem. I suspect you are right, I probably hurried the time between finish coats a little. The product sheet said allow 10 to 15 minutes between coats and I think I waited at least 10 minutes, but maybe I should have waited 20 or 30 minutes between the additional two coats of paint to be safe. I didn't know what solvent "pops" were and that the paint had to flash off completely to prevent them. I am sure I used the right reducer (DT870) for the temperature when I painted. I also used all PPG products from DPLF90, K36 and Concept. I am pretty sure there were no pinholes in the surface before applying the top coats, but I can be 100% sure. I can easily repaint the trunk lid, but I suspect I may have a few pinhole "pops" in other areas of the body, so with the directions above hopefully I can repair them without repainting. This is my first painting experience with acrylic urethanes. Other than the small pinholes, the lid turned out quite nice after color sanding. Next time, I will be sure to wait a little longer before applying the additional coats of paint.

One question: If I find "pops" in the paint on places I haven't color sanded yet, is it OK to do the repairs first, i.e. just clean the "pop" well and apply the small drops of paint, let dry well and then color sand? I think I can check the painted surfaces before color sanding to see if I have other "solvent pops".
Rusty Nelson
 
Rusty, I guess you could however I prefer to do it after it has been honed once.

One of the other things we do is after something has been painted and dried overnight, we like to "knock the top out of it" by wet blocking the panels to take the sealed top layer off so any trapped solvents can release. Often times we also will force dry the paint after this as we are trying to make the paint shrink all it is going to do. Then we will start wet blocking to allow the surface to flatten and then "shell-up". If the panels are flat and you encounter any boo-boos, you can more easily repair them once the paint has been flattened (blocked).

.
 
I had to fix my clear coat on my car and I did what Brent described and you can't see the repair. I carefully knocked down the paint build up with a nib file before wet blocking and polishing.
 
Pooch,
DPLF90 is a black colored Lead Free epoxy primer/sealer. There are several DPLFxx primers/sealers in different colors. Probably the most common is DPLF40, which is a medium gray/brown color. K36 is a light gray gray sanding primer. Concept is a single stage acrylic urethane top coat.
 
Reason for asking, is are they all the one brand?

Years ago, I saw a job go real bad with solvent boil. (you guys call it "pop").

One brand of primer, and it was "dry" for weeks, then topcoated with another brand and it blew bubbles like a kid with a bubble blowing toy.
 
Also, years ago, we had 2 main topcoat manufacturers....Dupont and Berger.

Am talking acrylic lacquer here.

These would mix, but not recommended, but sprayable.

There was a third smaller manufacturer called Regal.

When Regal was mixed with Dupont, the paint would instantly go to a quagmire, much like 2K when it has more than half cured in the tin, like mushy glue.
 
wrndln said:
Yes, they are all made by PPG.
Click to expand...

Then , you may have a claim, if the problem is in the paint itself and not the bondo or other, contact the manufacturer.

If you used all of their products, and the total thickness from metal or bondo is no more than 150 microns, they may do something for you, dunno.
 
The final finish fillers used these days can easily cause pinholes also. Vigorous mixing of the filler and the hardening agent can cause air to get mixed into the filler and therefore there will be small air bubbles in the finished product...most often in the form of a pinhole. Not long ago a friend was having trouble with pinholes. After examing the final sanded surface of the filler (he used a high quality one), it was full of pinholes. I have attended many body shop paint seminars over the years and they usually warn against vigorous mixing of the agents. I have had similar problems over the years and when I mix differently the holes all but disappear. They also warn against over catalyzing the fillers to "speed up" the process. I have had holes appear that way also.

Just another common problem causing pinholes.

Its no wonder body men enjoy mucho cervezas!!!! :D
 
Any pinholes in the filler should have been picked up after the primer after the guide coat and after the wet rub before any paint goes on.

30 years ago, when the filler was dodgy, we used to wire brush the filler when it was ready for primer.

Not so much for pinholes, but for major holes (up to match head size), that may be lurking just below the surface.
 
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