Mottling/poor atomisation in basecoat

  1. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England

    I’m having major problems whenever I go to spray BMW Black Sapphire Metallic basecoat. I’ve tried numberous different things to combat the issue but I never resolve it and it never cuts out properly without rubbing through to my basecoat.
    There is another video pending upload that I will post later

    Here are the basic facts and figures
    Panel sprayed with cellulose filler primer over Upol barcoat or isolater as it’s also know.
    Paint wet sanded. Forgot to guide coat so some areas are rough but that can be easily sorted out.
    Sanding scum washed off with water.
    Tetrosyl pre wipe degreaser used to clean panel. This product visibly flashes off as soon as you’ve applied it.
    1 part Closterman Coatings Merlin BMW black Sapphire Metallic
    1 part Pro Spray A116/A-116-1 medium basecoat thinners.
    I have also tried 120% thinners
    I think 120% is too much because I got blooming, which I’ve only ever had once before from spraying in damp conditions.
    Clarke AP16GF HVLP spray gun 1.4mm tip
    Running between 35-45psi input pressure read on gun pressure gauge.
    Fluid turns anywhere between 2-6 turns out
    Fan between 1/4 to 1 1/2 turns out.
    Another gun I have used is
    No make, budget conventional gravity fed with 1.5mm tip.
    Air pressure up to 50 psi

    Paint is not filling onto the panel nicely
    It is coming out in blobs
    Not as severe as if air pressure loss but noticeable.
    Paint is in speckled haze type pattern
    Never smooth
    Like results you get from spray can
    Paint will pile on smoothly but only if you move gun very slowly or pause
    Looks fantastic but then you see the runs.
    The primer I sprayed went on the panel lovely and smooth through a 2.2mm tip. It would never spray through a 1.5. It just spluttered all the time.
    I’m tempted to try my base through my primer gun because I don’t know what else to do.
    Same rubbish all the time. At my whits end.
    PS. Is it possible to upload photos from iPhone without url? If not; how do I? I have some nice clear photos. Shows what’s going on.
    Any help appreciated. This projects been going on for years and I just wish I had someone watching what I do and telling me what is going wrong when I spray basecoat.
    Thanks.
     
  2. Ruffian Member

    Messages:
    2,099
    Location:
    Devon UK
    Looks like halo of filler repairs,
    Edges around the screen possibly could be struggling with a lack of scotching/prep work.

    Have pressure are you painting with?
    Seems the metallic could be too course for your fluid tip but I cant comment too much as dont know what gun your using and never used that paint either.
     
    Edward Yemm likes this.
  3. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    How are you measuring the air pressure with the trigger pulled or not?
     
  4. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    The rear windscreen is a difficult to get paint under. If I could I’d remove it but it’s one of these modern ones that is glued in. Paint is going under it in spots and it’s not lying flat. I’m not too bothered about that as it’s near impossible to paint and it’s out of sight. As long as it’s covered by base and clear coat I’m happy. That speckled pattern of paint under the window is how it starts off all of the panel. If I slow the gun down or make a second pass over the area the paint fills better but it’s still like a load of tiny little hills with rivers between them. If I bring the gun to a stop paint flows really smoothly. There was no filler in a lot of the problem discoloured areas. There was Upol barcoat under the filler primer and that is what’s causing the edge mapping wherever I have sanded through to the barcoat. I think I’m possibly getting the reactions and lack of coverage in places because the thinner is not drying up fast enough. Maybe? Thanks for the reply.
     
  5. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Air pressure is before trigger is pulled. The “Gunman” on YouTube ran up some HVLP spray gun. He pulled the trigger in and said he was running 10 psi on the gauge with the trigger pulled in. That’s roughly what I was using but i had less psi on the gauge when I dropped the input pressure down to 35psi input. It barely registered 5psi when I pulled trigger. I could wind my water trap/regulator up to about 60 psi max. The gauge at the regulator was at 50psi plus when the gun was at 43psi input pressure. Thanks for the reply.
     
  6. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    Use the upload a file button below txt box
     
    bert and Edward Yemm like this.
  7. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    Usually need 30psi with the trigger pulled for the correct pressure as example devilbiss gti pro recommended air pressure with trigger pulled is 2bar (approx 30psi). Set air pressure with trigger pulled
     
    Edward Yemm likes this.
  8. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    I was trying to get the pressure this high. I’ll try again tomorrow. I just don’t want to break my spray gun. It says never exceed maximum input pressure of 43 psi. Its got 3 bar next to that though? Will my gun only get damaged if I plug it straight into the unregulated 120psi port on my compressor? I really don’t know much about what psi breaks guns. Thanks.
     
  9. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Thanks. I’ll try again tomorrow. I’ll post the other video I made as well.
     
  10. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    In the manual it lists operating pressure as 20 - 43 psi, I can’t find max air pressure listed

    Also has this

    Paint does not atomise (comes out in blobs).


    Paint is too thick.
    Air pressure is too low.


    Add thinners. Increase air pressure.

    As you have 1:1 paint and thinners then air pressure us to low

    Not sure about 120psi

    With no paint in gun pull trigger and slowly increase compressor regulator pressure until air pressure at spraygun is 30 psi then try that. If the gauge on the spraygun has a control open that fully first
     
    Ruffian likes this.
  11. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Thanks. I’ll wind my regulator up until I get that 30 psi. I’ll just use the failed base as a guide coat. Hopefully all problems will be resolved at 30psi. I’m convinced that the reactions and poor coverage over that barcoat is from piling 120% thinned paint on in too high a build. Cellulose primer loved it though apart from some solvent pop. Too high a film, solvent trapped me thinks. Barcoat is supposed to stop all reactions???? Something seriously not right if it doesn’t. Try again in the morning. Thanks.
     
  12. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    Set the air pressure with the fan control open as closing the fan control will increase the air pressure
     
  13. Slowcoach Member

    Messages:
    237
    Location:
    Bedford
    “There was Upol barcoat under the filler primer and that is what’s causing the edge mapping wherever I have sanded through to the barcoat. I think I’m possibly getting the reactions and lack of coverage in places because the thinner is not drying up fast enough.”

    If you primed the whole panel over the bar coat and didn’t reprime where you went through then that’ll cause the reaction.
    Can’t help on h v l p, never used one. Make sure the air cap is throughly clean.
     
  14. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Thanks. I’ll make sure I re prime any rubbed through areas of it then. I didn’t know much about barcoat. I only ever found one forum post about it after years of searching wrinkling/cracking defects. Years of asking around as well. No one knew the answer. Not even my local paint supplier. Was just told to use thinners over the affected area until one day it didn’t work and the reaction spread like wildfire. Glad I found out about barcoat. Only found one video about it and some Russian guy is using it when he gets a reaction in his basecoat. He sands back the patch of barcoat then carries on shooting the base over the top of it. I know it says “primer must be used over barcoat” on the can. He must have been lucky?
     
  15. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    What size air compressor have you got?
     
  16. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Photos of defective basecoat
     
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    • 20F5AA2A-B25C-492B-A892-92A00047C3CA.jpeg
  17. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    100 litre 3hp 14.6cfm. I found out on a website that the true CFM of these is less than 11.
     
  18. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    For flat/large panels the fan should be all the way open, then overlap by approx 50% to get coverage. In the first two pictures is that a glossy finish? Basecoat should not be glossy
     
    mr haynes likes this.
  19. carbon

    carbon Member

    Messages:
    1,412
    Location:
    S. Glos. U.K
    Think the spraygun manual quotes 9.5cfm so compressor should be big enough
     
  20. Edward Yemm Member

    Messages:
    90
    Location:
    Forest of Dean, Gloucestershire, England
    Yes. That’s right. Should be able to push enough cubic feet per minute down the airline whether the tank is full or compressor is running to build up air. At least Id hope it does. I’ve got a plastic coil hose from compressor to water trap/regulator then a 10mm hose between there and the gun. I have a Motor Guard mini desiccant dryer filter off the bottom of the gun then a machine mart adjustable regulator between that and the gun. If I can’t make the 30psi trigger pressure you mentioned then I’ll try ditching that desiccant filter. It’s only on there as I thought the bad basecoat may have been down to moisture but it clearly isn’t. Thanks.
     
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