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  1. #1

    Default Weld Thru Primer

    Hello,

    I am getting ready to weld my cowl back together. Once it is welded, access to the weld seams will be severely limited, although I do plan on trying to brush some seam filler at the seams that I can reach.
    Since there is limited access after the panel is welded in, I decided to try some weld thru primer because I do not want to ever have to remove this panel ever again.

    I have not had good luck with welding through zinc in the past.
    I noticed many recommendations for the Upol copper based weld through primer, better conductivity for better welds.
    But I also read that copper is a bad idea as it will set up galvanic corrosion.

    The last thing I want to do is to assemble this with a product that will cause corrosion. Again I do plan on seam sealing afterwards but may not be able to reach every part of the seams.

    I know epoxy primer is also a good choice, but unless it is sold in spray cans, I am not set up to mix and shoot paint.
    I have already sprayed the copper stuff on, I can remove it if need be. I also have a can of zinc weld thru here.

    Would I be better off leaving the copper at the plug weld locations, and spraying the zinc in between? That way it will weld better but still provide some protection?
    The car will not be driven in the winter, is the copper primer going to cause corrosion? Is it not enough corrosion to worry about?

    Thanks for any advice
    I need to get this car back together, as it has been sitting for 2 months and I am running out of enthusiasm for the project.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  2. #2

  3. #3

    Default

    Thanks for the links. Those repair videos were pretty informative!
    i found some of the same conflicting info on the hamb.
    I am taking off the copper, luckily it wipes off with lacquer thinner.
    Then I will reassess.

    I was wondering if I put some seam sealer between the welds, (after primer) would the seam sealer melt out to the edges of the pinch weld flanges?
    Obviously I would test this out beforehand. I would think that too little would be a waste of time, and too much would become a sloppy mess lol.
    But if I could get that to work, then I would not have to worry about reaching back under the cowl with an acid brush.

    I’m new to this level of bodywork, in case you hadn’t noticed lmao

    I am also finding out that a lot of weld thru primers can’t be painted over, so I have to be real careful masking everything off.
    Then I see they have self etching weld thru that can be painted over, there’s so many products and they all say they are the best
    I’ll do a little more research once I get all the copper stuff off
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  4. #4

    Default

    Now that the copper is off, I will look into 3m products. I did see using panel adhesive instead of plug welding but that does not sound like the way to go for this repair
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  5. #5
    FEP Senior Member
    Join Date
    Apr 2016
    Location
    Sprague River, OR
    Posts
    757

    Default

    SEM has a weld-through primer that I've used on a couple different projects. No issues yet after a few years.
    Join The Conversation
    http://www.youtube.com/basinmotorsports

    '86 Hatchback V6 / Auto Restomod (For Sale)

  6. #6

    Default

    Thank you! I am looking into that now
    sem and 3m seem to be the front runners as far as reputation

    Thanks for your review over time, it is very helpful
    many places give reviews about the application/welding aspect but never follow up on the durability over time aspect of these products

    unfortunately it looks like sem discontinued weld thru primer in 2018
    bummer
    Last edited by massacre; 06-02-2020 at 10:03 AM.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  7. #7

    Default

    So I picked up some Zinc based 3M weld thru II at Airgas.
    Thank you basin motor sports for the suggestion!

    I also ordered some Bloxide which is aluminum based.
    Zinc should be slightly better than aluminum for corrosion protection, and definitely better than copper.
    But zinc welds like crap, and that bloxide stuff seems to be the real deal after watching a couple videos. They get x-ray quality welds with it. And you won’t get zinc poisoning trying to weld it. No inclusions and no porosity of the welds, which is a given with zinc.

    So my plan is to apply the aluminum based primer only where the actual plug welds will be made, with zinc in all the other areas. Not exactly sure how I am going to achieve that yet, but I have a couple ideas. Prob will apply the zinc, then clean off the plug weld spots and apply the aluminum primer with a q tip.
    I know, that sounds like a lot of work and it is. But I don’t mind doing it for peace of mind, trying to get the corrosion protection of zinc without all the welding problems that it causes.

    The Eastwood platinum rust encapsulator that I used is aluminum based, and it went on like butter and took topcoat like a champ.
    but I didn’t weld through it, I was able to weld first and then apply the encapsulator, seam sealer and then some black stone guard type of paint.
    i don’t have that luxury once this piece is welded in, so I am just trying to protect the metal the best I can.

    I’ll post up once some results once I get to that point.
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

  8. #8

    Default

    So I looked up the melting points and boiling points of both zinc and aluminum compared to steel.
    On the galvanic corrosion scale, zinc and aluminum are right next to each other as far as corrosion protection, with zinc having a slighter edge. But zinc is not a great conductor of electricity, and welds like crap. Aluminum is a great conductor and does not weld like crap.
    So although they offer similar corrosion protection, the melting and boiling points of the 2 as well as the welding characteristics are quite different.

    melting
    zinc = about 800 degrees f
    aluminum = 1220.58 degrees f

    boiling
    zinc = 1665 degrees f
    aluminum = 4472.6 degrees f

    steel melting point = 2600-2800 degrees f
    steel boiling point = 5252 degrees f

    So it would appear that even at the melting point of steel, the aluminum should not boil (burn off) while the zinc would be long gone.

    So what I have decided to do-
    paint the upper flange with 2 thin coats of 3m zinc weld thru primer, with 1 thin coat of aluminum over it. The upper flanges are a lot thinner than the lower flanges. The aluminum coat on the upper is more for conductivity.

    The lower flange will be painted only in the aluminum, since the welding area and puddle will mostly be on the bottom flange. This area will see the most heat. I am hoping that the higher melting and boiling aluminum will help the zinc to not burn off.
    aluminum melts at 1220 deg f and zinc boils at 1665. It’s only a window of 400 degrees or so, but I’m hoping that the zinc and aluminum will melt together, forming a good corrosion protective surface, but also retaining good welding characteristics. I think if I am careful and go slow and move around, I can achieve this. I will also be seam sealing everything I can reach, but not sure if I can reach all areas with the seam sealer.

    This whole thing has been a huge learning experience. Researching this has been tedious but also very interesting.
    i don’t usually get this carried away, but the cowl sees water, that is what it is designed to do.
    Not planning on driving it in bad weather, but I live in MA where the weather can turn on a dime and unexpected heavy thunderstorms are common. Not driving in winter either so not worried about salt. Just worried about water creating a galvanic cell between the 2 metals and causing corrosion.
    This repair has set me back quite a bit on this project, I’ll be damned if I have to do it over again. Want to only do this once lmao
    79 Zephyr, 4.6L 4v/4r70w swap, with team z front and rear suspension, 8.8 and upgraded brakes and coil overs. Running Holley Terminator X Max.

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