I've rebuild the dash of my 1970 Challenger and I painted the lower metal surfaces using a simple black spray paint (semimatt). That was no problem with the dash itself...

When coming to spray the sheetmetal doors for the ashtray and for the glovebox - they turn me mad!

I sanded them down, washed with thinner and sprayed a primer on that based on synthetic resin. The primer covered proper - still no problem.

But when I spray the semimatt black paint on, I get some "dots" in the surface that "eat" the paint - throught the primer! It looks like small vulcanos. Where the primer was before, naked metal appears...

Then I grinded it away again, primed again, sprayed semimatt again - and it happens again!!!

I talk about one or two such "dots" on each part - as on the pic below.

To be honest: This black semimatt paint was just easy available in the supermarket and it does not say on the can what it really is - but I use it for years and paint everything and I cannot remember that I had those dots ever before... just on these two pieces of sheetmetal.

What's that???

It's what known as a "fisheye" in the paint trade, the cause is usually wax, grease, oil, silicone, etc that is present on the part, or the air where you are spraying paint,...it could be as simple as the oil in your skin if your handling the part with a bare hand, or the type of "thinner" your using to clean the parts, you'll want a highly evaporative cleaner to wipe down the parts prior to painting, some thinners can leave a residue....


Mike

Try spraying several (2-4) very light coats of paint until the surface has full coverage, allow each to flash off fully, followed by a wet medium coat or two. I've seen this technique eliminate persistent fisheyes when using rattle-can paint.

If you've sprayed w-d 40, any vinyl cleaners, used certain oils or even caulked your windows in the shop recently then this can happen from contamination in the air... air out the shop for a few days and try it again... we had it happen after one of the guys opened up a rear end case for inspection in the metal shop... just the fumes from the diff. oil in the air caused the fish eyes on all our small parts we were detailing nearby...
Silicon based products are the worst culprits.

Sand the primer down and let it sit for a day or two before painting the black.

What is the recommended cleaner for this type of prep work?
I have used MEK in the past - looking for other suggestions from the professionals!

Wally.

What is the recommended cleaner for this type of prep work?
I have used MEK in the past - looking for other suggestions from the professionals!

Wally.

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I usually use a good qualty laquer thinner (only on bare metal)... Prep-sol paint prep cleaners, cheap laquer thinners often leave a residue, even if there's no "fisheye" present

I've seen products such as prep-sol or sher-will clean made by sherwin williams cure those fisheyes when lacquer thinner won't. Here we can get rattle type cans mixed to our color. Maybe you could too and mix in some fisheye eliminator. It sure seems like a type of silicone contamination to me.

They could also be solvent popping.

Was the metal and/or air temperature cold?

With solvent popping, this flaw happens after you trap solvents under the outer skin of paint that dries quicker than the underlying coats. The solvents break through and cause a pop.

A couple tips- make sure everything is warm, including the piece you're painting, the paint and the air.
If you're using aerosols, also be sure they're completely mixed so you're not getting a thinner than normal shot of paint.
Don't spray your coats too heavy and wait for them to flash off well between coats.

Rick

Thanks to you all!

Those fisheyes (good to know a name for the EVIL) are indeed special. I painted dozens of parts that way and found this particular effect only on these two parts, on these two doors from the dashboard.

The special thing is that it happens again after grinding the paint off to the bare metal, cleaning again and priming again - at the same place (and of course at the second time you'll do it carefully).

So I wonder if there is some grease or anything in that old piece of metal itself. If there may be some microscopic crack or pipe or blowhole in the material that allows any residue to stay there.

I'm going to try again, sand the color down to the metal again, may be I'm going to warm it up and let it rest in solvent for a day and clean again using acetone and let it dry in a warm area for a while. I'll coat it with primer and put it in the oven for an hour and sand it slightly and may be do a second pass with primer - and then try again with light coats of paint.

The idea was to quickly re-coat these two parts in black before reinstalling - now I spend some hours for them...

Rick is right. Warm paint and warm parts equal a better paint finish quality. Another technique I use sometimes they show up on a part I'm doing, is that I get rid of them by rubbing/touching the fisheye with my finger tip until it stays covered with paint. I then "lay off" the paint with my finger to smooth out the spot I touched. Try keep the area you touch-up as small as possible, and work quickly befor the paint dries, so it can flow out. Then I respray another coat of paint to help the paint flow out and hid my touch-up. I get away with eliminating the odd fisheye with this technique more times than not, and depending on the part, it is hard if not impossible to see where I did it.....not always though.

I've also discovered to BEWARE of latex/rubber gloves!!! Some brands leave a residue that causes fish-eye city!
I also use the technique stated above of two real light coats first--let em dry. The paint normally.
A real light coat doesn't have enough paint to move (flowout) therefore the potential fisheye remains covered. Subsequent coats then bond to the light layer.

I had a problem that the compressor was spitting oil .My filters let it past. It wouldnt show up in primer or base but the clear would fisheye.Ck your filter and your tank to make sure they are clean.

Not sure what product you're using , but i have had trouble with synthetic primers in the past as the cure out took a very long time, might be outgassing when topcoat is applied, if you didnt use paint grade reducer in the primer could cause this also. I like the alcohol based pre-cleaners as it will remove all oils and contaminants. Acetone and mineral spirits have petroleum distillates in them.

X2 on the touchups, i use a paper match stick by the fuzzy end and dab into the fisheye, let flash and recoat
Environment is key as others said, oils in air etc. , heat source , kero?