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Ghost line on a welded seam

Discussion in 'The Hokey Ass Message Board' started by painkiller, Nov 27, 2010.

  1. painkiller
    Joined: Feb 10, 2005
    Posts: 135

    painkiller
    Member

    Mig welded seam on sheetmetal (butt-weld) . Ground pretty smooth, skim coat of evercoat putty, urethane primer, Dupont chromabase and urethane clear.

    2 months later I can see a ghost line where it was welded.

    What did I do wrong?
     
  2. Brandy
    Joined: Dec 23, 2004
    Posts: 5,286

    Brandy
    Member
    from Texas

    Was it a full pin butt weld or no?
     
  3. metal man
    Joined: Dec 4, 2005
    Posts: 2,949

    metal man
    Member

    Hate to say it,but sounds like you ground it too thin.
     
  4. 66gmc
    Joined: Dec 4, 2005
    Posts: 580

    66gmc
    Member

    what brand primer, it doesnt sound like you used a sealer so the base could be biting into the bodywork underneath.
     

  5. oldcarfan
    Joined: Jan 7, 2010
    Posts: 315

    oldcarfan
    BANNED
    from missouri

    not a good enough weld ( has to welded solid, even tack welds every 1/2 inch will split) or like metal man said ground to much of the weld off.
     
  6. painkiller
    Joined: Feb 10, 2005
    Posts: 135

    painkiller
    Member

    Seam was welded solid . Must have just ground it down too much.

    What is a full pin butt weld?
     
  7. Full penetration butt weld I'd say ??
     
  8. Maybe the weld expands and contracts at a different rate than the surrounding sheetmetal when in the sun or cold.
     
  9. The37Kid
    Joined: Apr 30, 2004
    Posts: 28,093

    The37Kid
    Member

    MIG on sheetmetal.
     
  10. BCCHOPIT
    Joined: Aug 10, 2008
    Posts: 2,597

    BCCHOPIT
    Member


    x2...
     
  11. bluestang67
    Joined: Feb 7, 2007
    Posts: 589

    bluestang67
    Member

    It is really best to give the materials time to dry . If you do a job like this in a couple days primers will shrink up . Great to let them set a week before you do any top coating .

    A good sealer is about the best thing to hold things back but then let the primers dry for a few days .
     
  12. scratchtown
    Joined: May 15, 2010
    Posts: 170

    scratchtown
    Member

    like bluestang67 said mud and primer both shrink i always take my primered car outside every day for a good week and let it bake in the sun then wet sand let it sit some more then primer again and repeat, paint bake booths some times do the same thing leave ghost line if done to fast from mud primer sealer base clear
     
  13. apound
    Joined: Jul 13, 2008
    Posts: 542

    apound
    Member

    I have had that problem before. I thought it was the filler shrinking so I started using dynaglass fiberglass filler first then regular filler to finish it. Cured it for me. Hope this helps.
     
  14. darkk
    Joined: Sep 2, 2010
    Posts: 456

    darkk
    Member

    I'm a retired body man and this is unfortunately a common problem with a million different legitimate answers...I always (if possible) put a piece of sheet metal behind my seams so I can penetrate fully to the other side. In most cases no one ever sees the backside. Use quality body fillers and don't rush the product. Always use manufacturers (between coat) times for body materials as well as paint products. If in doubt,a little extra time between steps costs nothing.
     
  15. chopolds
    Joined: Oct 22, 2001
    Posts: 5,933

    chopolds
    Member
    from howell, nj
    1. Kustom Painters

    All good answers, and it could also be that the MIG seam is more rigid than the surrounding sheet metal, so it doesn't flex the same, or heat and contract the same.
    Problem is especially prominent on dark colors!
     
  16. Harms Way
    Joined: Nov 27, 2005
    Posts: 6,869

    Harms Way
    Member

    This is what I was thinking right away,... (Guess how I know ? :eek:)
     
  17. squirrel
    Joined: Sep 23, 2004
    Posts: 48,790

    squirrel
    Member

    That's not how steel works....
     
  18. The37Kid
    Joined: Apr 30, 2004
    Posts: 28,093

    The37Kid
    Member

    I'd like to seesome lab test on MIG vs. Gas or TIG on sheetmetal. Butt weld two pieces, grind smooth with parent metal and test for penatration and strength. My guess is that MIG is the weakest of the three.
     
  19. squirrel
    Joined: Sep 23, 2004
    Posts: 48,790

    squirrel
    Member

    if you want a mig weld to be strong, don't grind it. Pretty simple.
     
  20. Harms Way
    Joined: Nov 27, 2005
    Posts: 6,869

    Harms Way
    Member

    MIG seems to be the hardest of all three,... I have GAS, TIG & MIG welded sheet metal,... In my experience TIG welding sheet metal (It seems to me it has really good penetration, and easier to work down), is the easiest to work with, than GAS welding and finally MIG.... But I am in no way a expert.
     
  21. Roger Walling
    Joined: Sep 26, 2010
    Posts: 1,149

    Roger Walling
    Member

    As a body shop owner I see shrinkage of the fillers and paint on all of my toys. We don't rush them, plenty of cure time, best products ect. 5 or 6 month down the road you will see distortions in the surface.
    I never colorsand and buff the finish coat until I feel that the shrinking process in complete. A year is a fair time to wait. At that time, a newly sanded and buffed wax job will renew your prized gem.
     
  22. Streetwerkz
    Joined: Oct 1, 2008
    Posts: 718

    Streetwerkz
    Member


    we run in to this sometimes when powder coating car body's.
    it's a VERY thin line when grinding the proud of a weld down to meet the surface.
    we have also found that both sides of the panels need to be ground, dollied, wheeled, etc so the metal is a consistent thickness front and back
     
  23. "All Metal" filler from USC.

    I use it (same process as above) on shaved door handles, patch panels and sections.

    Dynaglass works also, but with dark colors on a hot day you can still (barely) see the weld line.
     
  24. The Hank
    Joined: Mar 18, 2008
    Posts: 779

    The Hank
    Member
    from CO

    Damn , I did both rear 1/4's on my car and epoxy prime / build prime / BC-CC .Now I'M worried! It took me a while so I hope everything shrunk. I did colo rsand it right away though.
     
  25. BillyM
    Joined: Feb 9, 2010
    Posts: 144

    BillyM
    Member

    IMHO, it's definitely the different hardnesses between the parent and the weld............mig welded? Mig is very hard, and very hard to eliminate this problem........
     
  26. chopolds has hit the nail square on the head. Even if you do every thing by the book but when you do your welds you used a cheap high carbon wire / rod with your mig or tig on thin sheet metal these is a very good chance you will get those sickining ghosts especially out in the direct sun on a hot day.
     
  27. painkiller
    Joined: Feb 10, 2005
    Posts: 135

    painkiller
    Member

    Not in the hot sun. It is right around the freezing mark here in MI.

    Thanks for the replies.
     
  28. CutawayAl
    Joined: Aug 3, 2009
    Posts: 2,144

    CutawayAl
    Member
    from MI

    ...... agreed, could be shrinkage of filler/surfacer.
     
  29. Antny
    Joined: Aug 19, 2009
    Posts: 1,071

    Antny
    BANNED
    from Noo Yawk

    Is it possible to post a pic of the ghost line? I'm not sure I get what you mean by that.
     
  30. painkiller
    Joined: Feb 10, 2005
    Posts: 135

    painkiller
    Member

    Not the filler. There is just a thin coat of putty.
    What I am seeing is a staight line. Not sand scratches and a bondo edge.

    Antny, I dont think it would show in a pic. Line is very faint and on a silver car.
     

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