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Thread: Weld Through Primer that actually works

  1. #1
    Senior Member r4z0r7o3's Avatar
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    Weld Through Primer that actually works

    After my first attempt using some overly-expensive copper/zinc based stuff, I took a more scientific approach with some new stuff.

    The goal here is to get a coat of primer in between two faces of material that are then welded together (typically spot/plug or lap welded). Then the primer protects the two inaccessible faces from developing rust due to moisture collecting/forming between. The accessible would be painted as per normal.

    I prepared three pieces of angle-iron and three pieces of 22-ga sheet metal, each in exactly the same way. First they all got a dry wipe-down. Next, I used PPG Acryli-clean with a fresh towel. Finally, again with a fresh towel, a full wipe down. The numbers above each pair (and corresponding numbers on the sample back-sides) indicate the number of coats.


    First coats, with a five-minute flash time.


    Second coat, again a five-minute flash time.


    Third coat.


    Final coat. Then they all sat in the same area for 15-minutes, low humidity, temperatures in the 70-75 range (my guess). The un-coated "control" sample is wrapped up inside the blue paper.


    Welder setup for all three samples. Total drying time was maybe 45-minutes to an hour.


    Control (no WTP applied) sample clamped up and ready for tacking.


    Control sample fully welded.


    Back side of the control, nearly full penetration of the 1/16 angle-iron was achieved.


    The two-coat sample was prepared with this razor-scraper. I removed about 1/4-in of the primer in front of the lap. This is necessary to get a clean arc-strike. In a real situation, this would be the outside (accessible) side of the part, so re-priming and painting the weld bead and scraped area is possible. The critical side is facing down in the pic, the side you wouldn't be able to paint later.


    Two tacks down. Notice the discoloring of the primer. There was a bit of smoke, but not intolerable. I had to step harder on the foot-pedal than the control sample, as evidenced by the just turning blue oxide layer on the sheet metal that's not present on the zero-coat control.


    First half of the stitch-weld, more smoke, more discoloring, but nothing ever got wildly out of control like with the "Copperweld" brand I used before (link above).


    Two-coat sample, weld complete. Notice the heat-affected-zone, it runs about a half-inch wide up on the sheet metal.


    Under-side of the two-coat sample, a bit less penetration than the control. There's some odd "drips" coming from the joint, but they're only on the surface of the primer. Similar discoloring of the primer as on the front-side.


    Went at what would otherwise be the inaccessible surface, with the corner of the razor. Light pressure results in light surface-scratches. The primer stays put and doesn't flake off or gouge.


    Extreme pressure (corner of the razor is flexing quite severely), same result. The primer stays put, only minor surface scratches are produced. I've got to admit, I'm quite impressed by this.


    Four-coat sample preparation, scraping the 1/4-in weld-bead landing zone.


    Two tacks down, LOTS of smoke, heavy discoloring, and quite a bit more heat was needed (basically, peddle to the floor).


    Middle tack needed so much heat, it started to burn through the sheet metal.


    Weld-complete, notice the bumps and rough surface of the primer (it was bubbling). You can also see how much heat I needed to put in, the blue oxidation is all the way at the back-edge of the sheet metal, about 1-inches back from the weld.


    Back-side of the four-coat sample. Similar penetration as the two-coat sample, maybe slightly more. The primer is much more discolored, but stayed in place.


    Went at it with the razor. Surprisingly the discoloration scraped off easily but not the primer. It stayed put, nearly identical to the two-coat sample. A lot more effort was needed to scratch through to metal.


    Here's all three samples in good lighting. You can clearly see how much more heat was needed across them.


    Note: Respirator is absolutely required with this stuff, unless you enjoy being sick. The WTP is "Seymour" brand, "PBE, Professional spray paint".


    Close-up of the label showing the part-number and details. The back-side has the standard spray-paint bullshit instructions, and mentions nothing about flash-time, dry-time, or recommended number of coats (hence the experiment).


    Conclusion: 1000% better than "Copperweld". A stark contrast even, because this stuff actually works. The noozle has a fan spray-pattern which is adjustable to any angle. The stuff sprays on pretty heavy out of the can, definitely not a "fine-mist" like you get with common spray-paint. Since it welds fine with TIG, there'd likely be no trouble at all using other processes.

    Interestingly, it seems to stick on better after heating the metal. Before welding it was easily scraped off with the razor. Easier than scraping off a piece of painters-tape, if that's any indication. After welding though, it seems quite tenacious and durable, abrasion-resistant even. Based on these results, it seems like the 1-2 coats range is about ideal.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

  2. #2
    Senior Member Wolfcreek-Steve's Avatar
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    That's great info, the next step is a salt spray test to see if it actually keeps the metal from rusting. I'm guessing that your copper/zinc stuff is for spot welding where the primer must not electrically insulate the steel.
    I normally just use the generic grey/green self etching primer, it doesn't seem to affect the welding much, smells good when burned, and if possible I squirt a creeping wax/oil product on the back side.
    http://kbs.justoldtrucks.com/cavity-coater/
    What is that squeaking noise?

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    You should try A/C tig and see if the cleaning action makes any difference in heat required.
    FLAME ON...!!!!

  4. #4
    Senior Member r4z0r7o3's Avatar
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    Quote Originally Posted by J. Vibert View Post
    You should try A/C tig and see if the cleaning action makes any difference in heat required.
    I can do A/C on steel?!?!?!?!?!

    /me runs off to google and youtube...


    Quote Originally Posted by Wolfcreek-Steve View Post
    That's great info, the next step is a salt spray test to see if it actually keeps the metal from rusting. I'm guessing that your copper/zinc stuff is for spot welding where the primer must not electrically insulate the steel.
    I normally just use the generic grey/green self etching primer, it doesn't seem to affect the welding much, smells good when burned, and if possible I squirt a creeping wax/oil product on the back side.
    http://kbs.justoldtrucks.com/cavity-coater/
    As in: dunk 'em in salt water and then let them sit in the sun for a month? I'm too impatient for that

    I think you're right about the copper stuff being intended for spot-welding, though after heating (and off-gassing and burning, and popping) that particular stuff literally peeled off the metal. The only places it stuck were those untouched by welding heat Basically the opposite of this stuff. Also, last I checked, zinc is electrically conductive At 86% I probably didn't even need to scrape the landing-zone, was just something I read online.

    Creeping wax, interesting, didn't know about that stuff. I wonder if good-ole-wd40 would work...probably too thick.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

  5. #5
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    Quote Originally Posted by r4z0r7o3 View Post
    I can do A/C on steel?!?!?!?!?!

    /me runs off to google and youtube...
    I honestly have no clue... I do know A/C provides a cleaning action. I also know many experienced tig'ers think you can't D/C tig aluminum but you can, and in fact it can provide a stronger weld.
    FLAME ON...!!!!

  6. #6
    Senior Member Wolfcreek-Steve's Avatar
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    WD-40 really isn't a very good rust preventative, except in short term use before it oxidizes off the surface. Works great for cleaning road tar off your car though.
    Copper has fluxing properties when used in steel welding where zinc will alloy into the steel and cause brittleness. (you won't get a strong weld on galvanized steel, unless you remove the galvanizing in the weld zone)
    What is that squeaking noise?

  7. #7
    Senior Member OCD's Avatar
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    You folks want something that's almost bullet proof?
    Been using this stuff like forever.
    Very thin consistency and goes a Loooooong way.

    Actually, the thinner the better.
    If you apply it too thick in even 1 coat you'll end up with solvent pops.
    Not cheap by any means but then again anything that is worth while is cheap.

    https://www.rustbullet.com/

    Clean your metal, weld away, clean again, take a syringe & inject it in between the plates.
    Shake excess off, spray the rest of the part and your through.

  8. #8
    Senior Member r4z0r7o3's Avatar
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    Ya, the light/thin coat did seem to work the best. No idea about the rustbullet difference, seems like same-stuff-different-name. The price is certainly similar.
    "Things that are complex are not useful, things that are useful are simple."
    - Mikhail Kalashnikov

  9. #9
    Senior Member OCD's Avatar
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    Everybody in Florida that has a boat and truck tends to back down the ramps too far during low tide and ends up with rusty pumpkin balls on their rear axles.

    Rust bullet is the only thing I've came across that takes care of that issue and stands up to the saltwater environment.
    And I've tried ALOT of different products.

    Best to sand blast first, solvent clean and then spray but it still sticks and does it's job on light to moderately rust substrates.

    Never tried applying to heavily rusted substrates.

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