Need a Primer on Primer

Discussion in 'Body Restoration' started by rcurley, Jul 21, 2015.

  1. rcurley

    rcurley New Member

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    Last time I painted a car it was 20 years ago and with Lacquer...boy that was a lot easier!

    :( So I sprayed my 79 with 5-Star High Build 2k DTM Primer Filler/Sealer (item 5425) along with their activator (item 5426). It was about 85 degrees in the garage as I was spraying it. I sprayed the fender the night before and everything came out good, but this second job did not go so well. The surface was extremely bumpy, as seen in the picture below.

    [​IMG]

    I then sanded this down a little bit (about 30 strokes) with 180, and this is what it starts to look like.

    [​IMG]

    I keep going for another 100 strokes with 180, and this is the result - finally getting to a smooth surface.

    [​IMG]

    So, looking for some advice as to what the cause is and how to prevent this from happening again. I tried to do a 50 % overlap in spraying, and I tried to go slow, but it seems like it is just drying too quick, not allowing the primer to flow out. I am spraying with a 1.7 tip. Is there a thinner I can use that might help this out? Am I simply going to fast or not doing enough overlap?

    Any advise on what I am doing wrong and how to correct is greatly appreciated.

    Thanks,
    Rich.
     
  2. Rick WI

    Rick WI Veteran Member

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    That coat with all the bumps was sprayed too heavy. Solvent was trapped. Increase pressure about 5 lbs and increase gun speed a bit if you spray again under same conditions.

    Increased pressure will evaporate a bit more of solvent before it hits surface and bust up primer a bit more.
     
  3. stevenp3762

    stevenp3762 BANNED

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    Reduce it ten percent with reducer or acetone. It will flow out better.
     
  4. rcurley

    rcurley New Member

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    Rick...thanks for the reply. I did try messing with the air pressure, it was at 20 pounds at the gun with the gun fully open (no paint, just air). The primer says to spray at 9 pounds, but I am figuring a drop from the inlet of the gun to the tip. On another section that I painted that day, I really slowed down and decreased the spray fan to a pretty good pin-point, and that area turned out a lot better. So that's got me confused with the thought that it was too heavy. The weird thing the whole time I was spraying this was I couldn't get the fan to go any larger than about 4 inches, when spraying from about 5 inches. Other (thinner) paints will go a good 8-9 inch fan with that gun, but the primer just won't spread. That is why I was thinking a thinner might be a solution, but not sure what type of thinner I can use. The technical data sheet refers to "1 PART Urethane Reducer - Nat’l Rule Exempt Reducer for compliancy", but I didn't see any part numbers listed. I'm guessing the Acetone will work as posted by stevenp.
     
  5. Mike Bozung

    Mike Bozung Veteran Member

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    Your 1.7mm tip is big.......but not big enough. See if you can get a 2.0.
    Mike
     
  6. jester1

    jester1 Veteran Member

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    1.7 will work when reduced.
    The 9 psi is at the cap not inlet. Depending on the gun used that could be anywhere between 20-45psi at the inlet.
     
  7. rcurley

    rcurley New Member

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    Do you know of any way of determining how much of a drop a particular gun has? That's a pretty wide amount. Based on that though, I would still have been pretty far off as I had it at 20 PSI at the inlet, only about 11 pounds higher than what the data sheet said to spray at.

    I guess I'll try on some scrap, adjusting pressure, thinner, tips, etc. Man, I miss the ease of lacquer!
     
  8. stevenp3762

    stevenp3762 BANNED

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    Divide the inlet pressure at the gun by 5. If your 40 lbs. Right at the inlet of the gun your 8 lbs at the tip., 50 lbs at the inlet, 10 lbs at the tip. Reading your fan size problem. I say take the gun apart. Clean it real well , get it to spray laquer thinner real well and strong. Then spray out Ll the thinner and blow the gun and cup dry with air. Make sure your laquer thinner is dried up and gone. Then mix your primer/activator and 10% acetone and add to the gun. Pump up the pressure and blast some onto a piece of the body, then adjust air up or down accordingly.... Hth Steven.
     
  9. stevenp3762

    stevenp3762 BANNED

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    Don't be so concerned about the air pressure gauge, use your instinct/ feel.
     
  10. earlysecond

    earlysecond Veteran Member

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    One obvious point. . . You sprayed when it was cooler with no ptoblems. Maybe it is not possible to spray, preferably, in the early morning? Otherwise, you've been given some good pointers.
     

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