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Welding before or after media blasting and epoxy prime?

Discussion in 'The Hokey Ass Message Board' started by divcotruck, Sep 25, 2013.

  1. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    I'm a little confused as I see different opinions on this. right now my truck has paint and rust. there will be some welding required as I have to fix some bent parts and rusty holes. my question is if I do welding before or blasting it and priming it or after?


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  2. ive stripped my down to bare metal then welded my patches but should of done the body filler after a quick shot of spi epoxy primer for the best protection..but they said what i did with the body filler before is ok..just not the best ...course i dont live in a area that has high humidy...so i wasnt worryed about getting the epoxy on fast after it was to bare metal..
     
  3. carpok
    Joined: Dec 29, 2009
    Posts: 389

    carpok
    Member
    from Indy

    It totally up to you I've done it several different ways. But I think what works best is to spi epoxy prime after striping. Don't spend to much time around the areas that need repairs. Cut out and make rust repairs, hammer and dolly work. Get the body as straight as possible. Then da entire body and put two coats of spi black epoxy ( it has a sheen and you can see body flaws ) then do your filler work on the epoxy. That gives good rust protection and adhesion of the filler. Ron http://www.southernpolyurethanes.com/perfect paint.htm
     
  4. 2X^^

    Plus if you know you need patch panels now, you may find other areas after blasting. This would save you some time.
     
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  5. oldolds
    Joined: Oct 18, 2010
    Posts: 2,725

    oldolds
    Member

    I was always told to grind and weld before sand blasting. The idea was that the sand is hard to get out of the metal even after grinding. I have done it both ways. Never noticed a difference.
     
  6. I was taught to grind the paint to bare metal then weld in the patch panel and then sandblast. HRP

    [​IMG]
     
  7. Lupe.
    Joined: Oct 2, 2011
    Posts: 114

    Lupe.
    Member
    from TX

    At the restoration shop I worked at we would:

    1. Strip car of glass, seats, door handles, etc...
    2. Sand blast
    3. Blow all sand off from vehicle
    4. Spray epoxy primer. We used DP90LF, which is a black epoxy non sanding primer made from PPG. The price is not too bad and it worked good for long projects.

    Anyways that's what I would recommend because after blasting your almost always surprised with what else was bad on the vehicle. Its best to just get all of the old paint and body filler off to see what your really working with.
     
  8. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    gentlemen thank you for these replies, your experience is much appreciated!!!


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  9. chopd top
    Joined: Jun 25, 2008
    Posts: 472

    chopd top
    ALLIANCE MEMBER
    from Florida
    1. HAMB Relays

    I agree! I too have done it several different ways and this is how I would recommend you do it. It saves (for me) a lot of back tracking and seemed to be more efficient.
     
  10. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    great stuff I think I'll tackle it this way!


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  11. 34toddster
    Joined: Mar 28, 2006
    Posts: 1,467

    34toddster
    ALLIANCE MEMBER
    from Missouri

    I'm with Hotrodprimer , I always do my repairs weld, grind then sandblast, it will help clean that weld so you don't have anything pop out of the weld to lift the paint, you almost always find more rust after sand blasting so I have a very small blaster that I blast my additional welds with. Have fun!
     
  12. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    thank you!!


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  13. I remove all the panels that will be replaced first. Then blast. That way the inner panels get blasted as much as possible. I will not work on rusty crusty metal. I have a small blaster on hand to clean up anything missed, or removed after blasting. (there is always something) I don't epoxy under filler, I use a light coat of PPG1791/1792 as a shop coat to prevent rust. As I do the metalwork I remove the primer, and epoxy prime after filler.
     
  14. Gearhead Graphics
    Joined: Oct 4, 2008
    Posts: 3,086

    Gearhead Graphics
    Member
    from Denver Co

    Im a fan of blast first. There always seems to be more under that needs work than you planned on. Might as well get it all out of hiding and fix it at once.
     
  15. theHIGHLANDER
    Joined: Jun 3, 2005
    Posts: 7,720

    theHIGHLANDER
    Member

    If you can see all the work, which isn't hard to do, weld/repair 1st is the way to go. For the reasons stated above, it treats the new metal to the same prep and cleans the welds as well. I never, NEVER, put filler over epoxy, ESPECIALLY over DPLF. And also, DPLF has 3 days or less depending on temp to remain 'non-sanding'. After which the entire surface coated with it will need to be scuffed to a minimum of a red pad, preferably 240. Even then it's no guarantee that you won't have some adhesion difficulties later on.

    Some may come on now and cry bullshit, if so keep doing what works for you. I know what can happen even in the most remote areas no matter how hard you try to prevent it. DPLF is especially prone to swelling from the polyester liquids in fillers and tends to raise "bulls eyes" on the repairs months later. Dark colors are really prone to it. Go figure...
     
  16. I can attest to the swelling. However it's more of a crap shoot as it doesn't always happen. For some reason the swelling comes from heat, whether its from a hot day or from a heat lamp. I tend to use a hair less hardner and have had good results. As for the adhesion, I've never had a problem with it.
     
  17. jbtine
    Joined: Nov 22, 2005
    Posts: 210

    jbtine
    ALLIANCE MEMBER

    After blasting a body part that will require some metal work I use PPGs DX579. Sprays on, rinces off with water and prevents flash rust. I don't have to worry about primer contaminating my weld. After my work is done on the part i do another application then epoxy prime the part. I think DX520 would work too

    http://www.bapspaint.com/docs/psheets/PPG/Automotive/Deltron/P-226.pdf
     
  18. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    I am removing the engine and trans In the next few says. I've already began removing all panels as it seems I'll have to literally start from scratch. I think the welding will be done before the blast, it just makes sense. ImageUploadedByH.A.M.B.1380294632.397021.jpg ImageUploadedByH.A.M.B.1380294648.764328.jpg ImageUploadedByH.A.M.B.1380294664.797794.jpg


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  19. jfreakofkorn
    Joined: Apr 13, 2010
    Posts: 2,640

    jfreakofkorn
    Member

    this is a good thread .....
     
  20. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    lots of great ideas on this, I've been a bit confused. I had one mechanic want to haut strip her and do the epoxy before welding and for some reason I had my doubts.


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  21. J scow
    Joined: Mar 3, 2010
    Posts: 489

    J scow
    Member
    from Seattle

    I would recommend if possible to do your cutting and grinding then blast then weld. If you look at HRP's picture there is a lot of ugly that gets covered by patch panels that could be blasted. If you live in a humid area like me you would prime it after the blast then clean and weld each area as you go. If you are in a dry area you can get away with bare metal for longer but one humid day can send you right back to the blaster. There are lots of ways to skin a kitten but I would think this is the best practice especialy if you don't have a big climate controlled shop.

    P.S. HRP no offense intended I dig your rides.
     
  22. The wonders and myths about epoxy before or after have been debated here many times.:) It, like most things will never be "settled" here. You just have to do your research and figure out what makes sense, and would work best for your situation. There are different ways to do this work, and not everyone agrees on how.
    Since I'm absolutely sure the way I do it is the very best and only way:D::rolleyes::D <<< (That means I'm joking guys!) I'll make one more pitch for blasting first. Other than a day or two of dirty work ( I generally leave that to the customer, or hire help for dis-assembly) This is what I get back to start on. Still hard dirty work, but WAY better than working on crusty shit! In the last pic. you can see where I cut it further apart after the initial blasting. I blasted that and other areas after final cutting. (it came further apart than this)
    I really can't see trying to work on and weld this stuff before it's cleaned up. Seems like the hard way to me.

    But whatever you decide, and however you do this, please continue to post progress. Cool project you have. Anyone willing to tackle a job like this has my respect.
     

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  23. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    this thread rocks


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  24. greybeard360
    Joined: Feb 28, 2008
    Posts: 1,335

    greybeard360
    Member

    I have done a lot of rust repairs. Best procedure to me is blast, spray a mist of Ospho on the bare metal... this will actually prevent rust from appearing on humid days. Do the metal work and then prime. You want the metal as clean as possible when you weld or it can get ugly. Use weld thru primer on the inside of all new panels that can't be reached once it is to be welded together, otherwise you will have another hole in a few years.

    I am doing a OT Cuda right now that had a quarter panel replaced at some point in time, it rusted thru and then someone RIVETED a piece of sheet metal on top of the hole and then bondo to smooth. This car has about 1/4 inch of bondo on the whole car. There are several other similar patches done all over the car.

    Do it right the first time and you can forget about it for a very long time.
     
  25. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    solid advice from another expert thank you


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  26. carpok
    Joined: Dec 29, 2009
    Posts: 389

    carpok
    Member
    from Indy

    All good advice, there's so much talent on this site that what keeps me interested.
    One thing you might keep in mind is who is going to paint the finished truck If you have a shop in mind you might talk to the owner on what products he uses and buy your material from them. Most shops have paint systems they work with from start to finish sometimes it stops the blame game down the road. If your doing all your own work pick a system that best suits your project and shop conditions. This sounds like a no brainier but it's important from how you treat the bare metals to final cut and buff.
    I had a neighbor stop the other day checked out my 55. After all the usual small talk. He said he has a boat he's working on and having a tough time getting it painted. So I said I would stop his business were he's working on the boat in the back warehouse. Long story short his prep was not suited for a fiberglass boat. And the final paint system a high quality SS poly urethane that you could spray only one coat then couldn't recoat for 24 hours. To boot he was planning on three different colors one being silver with a 1/4" strip between colors. He trying to do it on weekend what time the business is closed. I think you can see what I'm saying. Pick your paint system and stick to it. Ron
     
    Last edited: Sep 27, 2013
  27. alchemy
    Joined: Sep 27, 2002
    Posts: 14,124

    alchemy
    Member

    Do you need one more opinion? I fully disassemble, cut out the majority of the rusty spots, then sandblast everything inside and out. You will probably find the areas you thought were bad are now even bigger, and that patch needs to be bigger too.

    If you make and install patches before cleaning, what is going to stop that rust on that folded edge you welded a patch to? Or the backside of the inner fender panel, or inside that rocker? Are you just hoping the patch will keep new moisture out of there?
     
  28. sunbeam
    Joined: Oct 22, 2010
    Posts: 4,219

    sunbeam
    Member

    There a place not to far from me that's builds stock trailers they paint all joints and laps with zink primer. He sez some burns off when welding but a lot doesn't and cow piss will rust things in a hurry. So with patches I follow his advice.
     
  29. divcotruck
    Joined: Jun 28, 2013
    Posts: 72

    divcotruck
    Member

    thank you all for this advice!!!


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