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Technical Epoxy Priming fresh blasted metal - a discussion.

Discussion in 'The Hokey Ass Message Board' started by 31Vicky with a hemi, Sep 24, 2019.

  1. So recently there’s been a discussion here about priming some fresh blasted metal.

    The one side and manufacture tech sheet says to commercial blast the metal and prime the fresh blasted texture surface.

    The other side says to 80 grit sand the blasting texture down to a smoother surface then prime it. The reasoning here is that it’s nearly impossible to wipe down the surface with any solvents, remove finger prints, or anything that may be stuck in the texture.


    So the second position here makes more sense, involves a shit load more labor and violates the tech sheet.

    What’s the best way?
     
  2. I don't always read instructions, but when I do, I follow them.
     
    Frankie47, partsdawg, lilmann and 4 others like this.
  3. Yep buzz it down with 80 grit for me.
     
    kidcampbell71 likes this.
  4. Smokeybear
    Joined: Apr 20, 2011
    Posts: 312

    Smokeybear
    Member

    The first time you see a fairly new (less than a couple of years old) paint job peel off in sheets, you'll wish you DA'd the surface before epoxy primer. Mechanical adhesion AND chemical adhesion is better than chemical adhesion alone.
     
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  5. I usually go with the instructions, unless I've had personal experience to dictate an adjustment in the recommendations. I blasted my coupe, epoxy primed, then surface primed, blocked and painted my coupe 25 years ago. No issues yet.
     
    osage orange and ABONES like this.
  6. john worden
    Joined: Nov 14, 2007
    Posts: 1,448

    john worden
    ALLIANCE MEMBER
    from iowa

    Blast, blow off with clean dry compressed air and prime immediately.
     
  7. woodiewagon46
    Joined: Mar 14, 2013
    Posts: 1,408

    woodiewagon46
    Member
    from New York

    You want your parts to be media blasted with walnut shells or some other media. Sandblasting will do the job but it's way to aggressive for most parts. I just had several parts media blasted and you could run your hand over them they were so smooth. Leave the sandblasting for tombstones and graffiti removal.
     
    Cosmo49 likes this.
  8. You have ZERO recourse if you have issues down the road and didn't follow the TDS.
     
    john worden likes this.
  9. squirrel
    Joined: Sep 23, 2004
    Posts: 43,503

    squirrel
    Member

    I usually blast, start doing body work, let it sit for a few years in my shop, then do some more bodywork, then when it's close I'll run a DA over it and throw on some urethane primer. Then more of the let sit/bodywork thing, etc.

    It's nice living where it's dry
     
  10. Ralphies54
    Joined: Dec 18, 2009
    Posts: 698

    Ralphies54
    Member

    All this talk about sand blasting!! What grit do you use to remove paint down to bare metal, could it be that the blaster is in a hurry and is using 2 ought when he should be using 4 ought?
    I've done my own blasting using 4 ought @ 100 psi and ended up with a glass smooth surface. Then lightly sand and a see through coat of etching primer, never had a paint job fail. Ralphie
     
    Last edited: Sep 24, 2019
  11. john worden
    Joined: Nov 14, 2007
    Posts: 1,448

    john worden
    ALLIANCE MEMBER
    from iowa

    Media and walnut shells certainly are useful in some applications but do not remove rust.
    Media blasted parts are smooth indeed and require additional work to provide "tooth" for primer adhesion.
     
  12. pitman
    Joined: May 14, 2006
    Posts: 4,690

    pitman
    Member
    from Hampsha

    In the Northeast, rust capital, many of us use a coal waste product called Black Beauty.
    The electric powerplants sell it.
     
  13. Didn't you get some of the rain this weekend:rolleyes:
     
  14. This is how I do it, right or wrong and it works for me.

    I sandblast the part/parts and then blow off any dust followed by using surface prep on the bare metal, I continue until the residue has been removed and clean it once more before spraying the etching primer.

    Granted it's slow and time consuming but again, it works for me. HRP
     
    36roadster and osage orange like this.
  15. oldolds
    Joined: Oct 18, 2010
    Posts: 2,761

    oldolds
    Member

    There are different grits of sand blasting sand and the above mentioned Black Beauty. 80 grit is usually a medium grit of those. A good blast and prime is what I usually do when I have a rusty project. I will not blast for just paint removal.
     
    rockable likes this.
  16. thirtytwo
    Joined: Dec 19, 2003
    Posts: 2,523

    thirtytwo
    Member

    25 yrs ago I was taught to blast then DP epoxy but I believe the product was better back then also I still have stuff that was done that way in1999 and no adhesion issues currently I use ppg industrial epoxy and do things the same way, I can’t imagine someone blasting a bridge then DA with 80 grit so I have kept my old methods for the most part , right or wrong
     
  17. RMR&C
    Joined: Dec 26, 2009
    Posts: 3,160

    RMR&C
    Member
    from NW Montana

    Seems like sanding defeats the purpose of creating a nice etch. Don't blast greasy or oily parts. Don't blast til you are ready to prime. Wear gloves when handling freshly blasted parts.
    Works for me...
     
  18. squirrel
    Joined: Sep 23, 2004
    Posts: 43,503

    squirrel
    Member

    Didn't get any this weekend down here, but today it's rained 2.5 inches so far, flooding, roads closed, etc. Still not bad in the shop, I have good insulation.
     
    osage orange likes this.
  19. wvenfield
    Joined: Nov 23, 2006
    Posts: 4,787

    wvenfield
    Member

    Did my frame with that. I'm not an expert but it did a great job. Blasted, primed and painted.
     
    osage orange likes this.
  20. dan31
    Joined: Jul 3, 2011
    Posts: 990

    dan31
    Member

    Just did my 64' Polara last week . Recycled glass media 40-70 grit ( Dustless blasting) use Hold tight 102 in mix and then wash down with it when done,dry with compressor then leaf blower ,even drier air . I epoxy painted the underside of hood ,fenders, trunk e.c.t. that day with no prep. Next day hit all "finished sides" with 120 grit da then paint. Did the undersides first because if there was any flash rusting the finished side is way easier to run a da over then trying to get into all of the tight areas on the undersides.
     
    osage orange likes this.
  21. I've been using black beauty (coal slag) for about 12 years. Only recently did I use a da and 80 grit after blasting. I had no adhesion problems in the past but the metal sure did look nice after the 80 grit pass. I use Kirker epoxy and have no complaints with it. I'm using the fine media and recycling it a few times which means it's way finer than the 1st usage. My thought about the da was that the metal is smoother. That should take less filler to achieve the desired end results. This whole subject has about 6 ways to get to the end. Some people take short cuts and get away with it and the others do everything as good as you can and the bird of paradise comes a long and takes the biggest dump ever on the paint job. Eventually, we all have to figure out what works in our shop and exp. level. Good luck to the O.P. You'll get it. :)
     
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  22. Fortunateson
    Joined: Apr 30, 2012
    Posts: 2,387

    Fortunateson
    Member

    Anything used to blast material is "media". Sand, walnut shells, aluminum oxid, etc. are all different types of media.

    Now what primer should be used on th fresh surface? Acid etch or epoxy? I lean towards epoxy. But I'm only an avid amateur so what do the no?
     
    Last edited: Sep 24, 2019
    osage orange likes this.
  23. the flatlander
    Joined: Apr 29, 2004
    Posts: 386

    the flatlander
    Member

    At our business Blastman, we’ be been blasting sheetmetal starting in ‘84. We use #80 garnet at about 65 psi. No pitting or warping! We offer to prime customer parts if wanted. PPG epoxy or for something’s Rustoleum. Old ( good) metal can sit a while if not touched. Good luck with that. We blast to bare metal & prime , depending on weather. ( we blast all inside & reuse material) good luck guys


    Sent from my iPhone using H.A.M.B.
     
    osage orange likes this.
  24. tb33anda3rd
    Joined: Oct 8, 2010
    Posts: 15,115

    tb33anda3rd
    ALLIANCE MEMBER
    1. Connecticut HAMB'ers

    I have done it both ways, without problems, sanding leaves a SMOOTHER finish which in turn, leaves less sanding of the primer before paint.
    I have noticed one thing about "raw" blasted metal, it does not weld as cleanly as a blasted piece that has been sanded. this leads me to believe there is still "sand" on the surface.
     
  25. oldolds
    Joined: Oct 18, 2010
    Posts: 2,761

    oldolds
    Member

    A friend of mine insisted that you should do most of your metal patching before blasting. For the reason you mentioned.
     
  26. 51box
    Joined: Aug 31, 2005
    Posts: 776

    51box
    Member
    from MA

    When I was doing my chassis stuff if a piece didn’t need mud... I would blast with fine coal slag, blow it off, epoxy prime wait an hour and then put the paint on. No sanding no touching the surface etc. it came out surprisingly smooth and had a great shine. Hope it holds up for a long time cause body work sucks to do.
     
  27. I can almost guarantee there’s microscopic sand residue shit in the low spots of the texture profile.

    This is the side I’m on.
    However they wrote/write those things so that the verbiage will cover their ass not yours.
     
    tb33anda3rd likes this.
  28. Just for general knowledge
    What would these cost to get these items blasted
    It was all clean metal that turned,
    no paint, no undercoating.
    Body , inside, outside, underneath on s cart.
    Frame and rear axle.
    BD391EDC-93F8-424D-B9AD-C84673BF13DD.jpeg 58D7E7B0-74C1-4BB2-B315-887F836D02B0.jpeg 93FAE741-53C3-4EF1-B31F-95FD19F8E120.jpeg B3D75502-27EC-4494-8B3D-28EF5A3D8FA0.jpeg EA2C036E-B310-49AB-B2F9-119D92F30696.jpeg D5C7CFD8-3E3D-433D-A40C-04C9710A644B.jpeg
     
  29. john worden
    Joined: Nov 14, 2007
    Posts: 1,448

    john worden
    ALLIANCE MEMBER
    from iowa

    In our part of the world "media" blasting uses the tiny plastic pellets which remove auto paint coatings leaving a smooth warp free but not rust free surface.
    "Media" blasting really took off during the auto makers peeling clear coat days. It was the preferred method to remove the failed factory finish with less chance of damaging exterior components.
    Other types of blasting are described more specifically as sand blasting, grit blasting, glass bead blasting, soda blasting, vapor blasting, walnut shell blasting etc and all have their uses.
    To me acid etch primer is overkill used on a sand blasted surface.
     
  30. john worden
    Joined: Nov 14, 2007
    Posts: 1,448

    john worden
    ALLIANCE MEMBER
    from iowa

    31 Vicky........ What blasting material do you want used?
     

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