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Thread: Blisters in base coat. Only after clearcoat, hours later

  1. #1

    Default Blisters in base coat. Only after clearcoat, hours later

    Been having a problem with a hood. I keep getting blisters under the clearcoat. Size of the head of a pin.
    I have bought new catalyst, Reducer, and clean the hood prior to paint with kw-901 grease and wax remover.
    Last repaint from yesterday, I sanded down to the light bondo layer then sprayed 3 coats of evercoat dtm high build.
    Sanded to 600 grit and cleaned again with wax remover.

    Base coat looked good. Waited 1.5 hours in Temps of 85.
    Then ckeacoat. Looked good but blisters formed under the clear.

    Ideas on the problem?

  2. #2
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    Quote Originally Posted by jerrys paint View Post
    Been having a problem with a hood. I keep getting blisters under the clearcoat. Size of the head of a pin.
    I have bought new catalyst, Reducer, and clean the hood prior to paint with kw-901 grease and wax remover.
    Last repaint from yesterday, I sanded down to the light bondo layer then sprayed 3 coats of evercoat dtm high build.
    Sanded to 600 grit and cleaned again with wax remover.

    Base coat looked good. Waited 1.5 hours in Temps of 85.
    Then ckeacoat. Looked good but blisters formed under the clear.

    Ideas on the problem?
    How many coats of clear did you apply and how long did you wait between coats?

    If it's applied too heavily without waiting long enough it can cause solvent pop which is like small bubbles and craters in the clear.

  3. #3

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    three coats of clear and 15 to 20 min between coats. Temps in the 80s during all this. This seems like solvent pop but not consistent across the hood. I did put 3 coats of basecoat on the hood.

    I waited 1.5 hours prior to clearcoat, would waiting longer help?
    PS: shopline JBPX basecoat
    shopline jc780 clearcoat
    Last edited by jerrys paint; 07-10-2022 at 03:17 PM.

  4. #4
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    Quote Originally Posted by jerrys paint View Post
    three coats of clear and 15 to 20 min between coats. Temps in the 80s during all this. This seems like solvent pop but not consistent across the hood. I did put 3 coats of basecoat on the hood.

    I waited 1.5 hours prior to clearcoat, would waiting longer help?
    PS: shopline JBPX basecoat
    shopline jc780 clearcoat
    If it's solvent pop the problem is probably not in the base coat. It will usually show more in the horizontal panels (hood, roof, trunk) than on vertical panels. The first coat of clear should be almost dry to the touch before the second and third are applied. The problem is caused by solvent being trapped in the lower coats by the upper coats drying before the lower coat gets rid of the solvent.

  5. #5
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    Another thing that can cause it is spraying with the air pressure too low. The clear doesnít atomise properly and the larger droplets of clear let too much solvent get on the surface. Be sure to set the gun pressure with the trigger pulled.

    Bob K

  6. #6
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    Quote Originally Posted by Bob K View Post
    Another thing that can cause it is spraying with the air pressure too low. The clear doesn’t atomise properly and the larger droplets of clear let too much solvent get on the surface. Be sure to set the gun pressure with the trigger pulled.

    Bob K
    I agree Bob and also using a fluid tip that is too large for the material being sprayed.
    Last edited by Len; 07-11-2022 at 10:04 AM.

  7. #7

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    Sagola 4500 with 1.3 tip bought from Ken years ago.

    Tip too large?

  8. #8
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    That sounds good. Do you have the fan wide open and the air pressure set at the gun with the trigger pulled? I donít know what that gun needs for clear but I wouldnít be surprised if it should be near 30 or 35 psi. Iím out of ideas otherwise unless you are moving the gun to slow and putting the paint on too thick, but if you do that you should get runs also.

    Bob K

  9. #9

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    Pressure is at 35 at the gun, about 11 at spray tip.
    I have slowed down my spray arm to keep the pattern wet as it warms up around here.

    I will spray tomorrow am and keep the coats lighter. Thanks for the advice so far

  10. #10
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    It worries me that you say 11 at the spray tip. Are you measuring it somehow or just guessing because of some political definition of HVLP. I must have an overactive imagination because I can envision someone setting the wall regulator to 35 psi and then 11 at the gun with the trigger pulled to try to accommodate the regulation tip pressure. Hope you are not doing that. I like 80 psi or more at the wall.

    Bob K

  11. #11
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    Default which hardener?

    JH7870 or JH7880 ? I'd use slow in those temps...

    Found a uk ppg link, weird its not in the us site (or google isn't showing me)

    https://uk.ppgrefinish.com/en/paint-...lvent-popping/
    Last edited by fj5gtx; 07-11-2022 at 08:56 PM. Reason: add link

  12. #12
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    Quote Originally Posted by fj5gtx View Post
    JH7870 or JH7880 ? I'd use slow in those temps...

    Found a uk ppg link, weird its not in the us site (or google isn't showing me)

    https://uk.ppgrefinish.com/en/paint-...lvent-popping/
    my thoughts exactly. i like the slow reducer in the warmer temps. i use 75f as my benchmark.
    b marler

  13. #13

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    repainted the hood today and it came out very good!
    First, thanks for all your suggestions but I think the problem was even simpler.
    I bought Shopline JBX paint for most of the car, but when I needed more paint, the shop gave me JBPX paint. At the time the counter guy also sold me more catalyst. He told me that JBPX requires less coats of paint.
    JBX requires catalyst. JBPX may require catalyst unless it has another item in the mix. I finally looked up my mix on the can and yes that item was there. So the paint I had did not require a catalyst and I was adding it. I assume that the paint was drying quickly and not releasing all the reducer so developed blisters.

    Learning lesson: Read the PDF very carefully when they sell you something new.

    This is the last part to put on the restoration project I have been working on for the last year. The car is ready for a test drive now!
    Jerry

  14. #14
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    Feb 2006
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    Quote Originally Posted by jerrys paint View Post
    repainted the hood today and it came out very good!
    First, thanks for all your suggestions but I think the problem was even simpler.
    I bought Shopline JBX paint for most of the car, but when I needed more paint, the shop gave me JBPX paint. At the time the counter guy also sold me more catalyst. He told me that JBPX requires less coats of paint.
    JBX requires catalyst. JBPX may require catalyst unless it has another item in the mix. I finally looked up my mix on the can and yes that item was there. So the paint I had did not require a catalyst and I was adding it. I assume that the paint was drying quickly and not releasing all the reducer so developed blisters.

    Learning lesson: Read the PDF very carefully when they sell you something new.

    This is the last part to put on the restoration project I have been working on for the last year. The car is ready for a test drive now!
    Jerry
    I was curious enough that I had to look this up... Here is a portion at the top of the latest tech sheet for JPBX.

    This updated TDS is intended for revised JBPX formulas (which contain J179). If using historic filed JBPX color match formulas (which contain
    J136) see historic version TDS - must use JH6028 hardener in the ready to spray blend for historic filed JBPX formulas.

  15. #15

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    Exactly, on the change in formula! And that article on vent popping was exactly what I was seeing.

    I only went back to the PDF because all of your ideas eliminated everything else.

    Jerry

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