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Thread: Craters in paint

  1. #1
    Join Date
    Sep 2007

    Default Craters in paint

    I have chronically had "fisheyes" or depressions form in my paint projects. They are not pin-holes caused by voids in the underlying strata but are shallow craters in the paint film.

    This has been an ongoing problem in gel coat at another facility and was a problem recently in polyeurethane at my new facility.

    Following the advice here and other sources, and installed a brand new, world-class compressor / air / paint system with more than 40 ft of iron pipe to the gun, in-line water traps and drains, sub-micron coalescing air/oil filters, a paper roll filter just before the dedicated "painting only" hookup, a new air hose and finally a new "tennis ball" filter at the gun (a new Finish Line III).

    I live in high and dry area of southern Calif. and have never seen any moisture/oil beyond the first in-line pipe drain 10 ft from the compressor. Still apparent contamination issues.

    The craters show up in the surface well above the original strata so I do not believe it is contamination in the surface being painted but am at a total loss to explain their origin.

    Could the paint be inadequately mixed? I am aware that gelcoat (polyester paint) topcoats have wax in them to seal the surface. Could the wax coalesce in the paint to form immiscable droplets?

    Thanks for the forum. I have lurked a long time and it is a great resource!
    Last edited by markgrubb; 09-17-2007 at 12:36 AM.

  2. #2
    Join Date
    Dec 2005


    try to think of everything. any desiel machines nearby, snacks, potato chips, french fries. wash yer hands well, wipe solvent on with one rag and use clean dry rags to wipe it off. are you applying it real real wet?

  3. #3
    Join Date
    Nov 2006


    Several years ago I was painting the underside of a hood. Since I knew it would not be seen since it was going to have insulation covering the paint I used it as an experiment on gun air pressure. I dropped the inlet pressure down to about 7# at the gauge with the trigger pulled and while spraying at such a low pressure I got a very nice looking clear coat, but after it dried I had those craters you speak of. (Solvent pop)

    That may not be your problem but it is my guess that it is your problem. I donít mean low pressure but only that you are getting solvent pop for some reason. Not enough flash time between coats, to much solvent, to slow of a solvent for the temperature, or other issues I havenít thought of.

    When I have a problem going on I try to get to the hart of it by changing only one variable at a time. I sometimes try to intensify the problem, to help me understand what is going wrong, hence lowering my air pressure to an unacceptable level to see what happens.

    Bob K

  4. #4


    I just finished sanding down my clear coat job, which was rough as a cutting board. After sanding it flat I found thousands of little bubbles sanded in half. I did not realize how bad it was until I shot the clear with a different gun. It would have turned out nice but the bubbles created thousands of craters.

    Welcome to the club.

    Now I think I am going to get out the 80 grit and start over from scratch.

  5. #5
    dave_demented Guest


    ahh the wonders of solvent pop.....

  6. #6


    i worked in the paint plant at nissan in the touch up department. we were given a list of things not to use that causes craters. certain deoderants, shampoos, hair sprays, hair gels, soaps, make up and other things such as that cause cratering. we would do a crater check before shift start. a guy would walk around to everybody with a panel of fresh sprayed clear on it and get you to shake your shirt sleeve over it. it would instantly crater the clear if you used one of the non-compliant items. i had to switch to using right guard deoderant because of that.

  7. #7
    Join Date
    Nov 2005
    Montreal, Canada

    Default Air entrapment is another source of simili crators...

    Gell coat is notorious for not atomizing properly. If you have large droplets comming out of the gun and laying it on thick, you can trap air in the paint film. This trapped air forms a single bubble which migrates to the surface and bursts, leaving a crater in the surface. Proper atomization (fine mist) solves that one.
    My 2 cents worth...

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