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Help with paint bubbling

Discussion in 'Technical Q&A' started by vincep99, Aug 21, 2014.

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  1. vincep99

    vincep99 Formula 3
    Owner Silver Subscribed

    Jun 8, 2009
    1,940
    #1 vincep99, Aug 21, 2014
    Last edited by a moderator: Sep 7, 2017
    I hope someone can help me. I have painted fairly often and never had this problem. It is with a spot repair just ahead of the rear wheel. There was some surface rust, so I sanded it to bare metal, cleaned it with automotive Wax and Grease remover, primed it, sealed it, painted it, clear-coated it. I am using Matrix Systems Urethane. Same procedure (prep, flash times, etc) I have used before, no problem. Started bubbling ~ 3 weeks after I painted it. Did the whole procedure again, same problem. It was 70F, low humidity both times. I sued the right reducers and activators. I drained all moisture from the compressor. I am using a Devilbiss gun.

    Here some pictures (no, it's not my 360, it's my DD), right side and left side. Other spots I touched up are OK.

    Looks like bad prep, I know, but I don;t know what I could have done better.

    The rocker panels were btw removed for the repair. And yes, these close-ups do show that I did not quite smooth out the small amount of filler that I did use on the vertical surface. But that is not where the bubbling is
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  2. PSk

    PSk F1 World Champ

    Nov 20, 2002
    17,673
    Tauranga, NZ
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    Pete
    #2 PSk, Aug 21, 2014
    Looks to me like you did not get rid of the rust. Need to cut it out and weld in new metal, and importantly epoxy prime otherwise the metal will sweat ...
    Pete
     
  3. 360Tom

    360Tom Formula 3

    May 9, 2013
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    Burbank, CA
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    Tom
    #3 360Tom, Aug 22, 2014
    That rust is going to constantly be problematic. You might get lucky and may be able to take a DA sander to it and grind some of it away to see if there is some fresh metal still.
    How old is the car it's on?
     
  4. vincep99

    vincep99 Formula 3
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    Jun 8, 2009
    1,940
    #4 vincep99, Aug 22, 2014
    Thans for the replies.

    It is a 2007.

    I did grind all the paint away to bare metal, but like you said rust is always a problem.

    I used etching primer, I will try epoxy primer next time.
     
  5. netman

    netman Formula 3

    Jun 17, 2008
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    OC SoCal
    #5 netman, Aug 22, 2014
    you need to use some sort of rust neutralizer
     
  6. cmt6891

    cmt6891 Formula 3

    Feb 25, 2008
    1,337
    Encino, Ca
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    Carl T
    #6 cmt6891, Aug 22, 2014
    +1 you can try Por15 as a primer/neutralizer then paint
     
  7. bpu699

    bpu699 F1 World Champ
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    #7 bpu699, Aug 22, 2014
    The rust is coming from the backside. Mine did this. Waterproof the backside.

    But honestly, once you have rust, it comes back. On my work van, I touch up with white rustoleum. Looks fine... On a white work van.

    Bo
     

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