The Jalopy Journal
Discussion in 'The Hokey Ass Message Board' started by old_chevy, Jul 6, 2020.
trying to decide what primer to use for autobody spot weld and plug welds
This is a popcorn thread ...
When I use it, I use zinc because that's what all the local jobbers carry. Some people claim splatter issues with it, others claim it is toxic. Ideally you want nothing to contaminate your weld pool, but you are probably using copper coated mig wire so that quickly goes out the window.
If you believe it works, I'd say use zinc because it is less noble than iron so it becomes sacrificial. Copper is more noble than iron so no benefit there.
I use zinc. And don't go crazy heavy, i just put enough to cover. And let it dry good before you try to weld. Heavy coats and not being dry is the reason for spatter. That's my experience.
Copper seems to have become the norm in the collision industry, and all those fancy spot weld machines seem to recommend using copper. That being said I've cut apart a few cars that had copper weld thru, and the seams were rusting.
At home I use zinc and have had no issues. I think the key is putting it on in a light coat, and clamping the 2 layers of metal around each weld tightly. If your having trouble with spatter or put it on too thick you can take a small screwdriver and scrape the weld thru off inside of each hole before welding.
Weld thru primer is meant as a sacrificial coating for when 2 or more layers of metal are flanged or overlapped together. Ive seen a lot of people spray it on everything, even when butt welding, which is a complete waste of time, not only that but it has almost no adhesion properties, meaning if you start putting other primers or topcoats over it, you may be in for a nasty surprise later on...nothing sticks to weld thru primer, and weld thru primer sticks to nothing.
Zinc...ever see what a penny does when ya leave it in a damp environment..
Pennies are 97.5% zinc and 2.5% copper.
Yup. If pennies were made of copper, they would cost way more than $0.01 to make.
I just got some of the upol weld Tru copper primer. I also have the 3m weld Tru primer. I'll test them both out and see what works best.
It always makes my welds act as if something is on the metal??? Because well something is on the metal .!!!!!!!!!!!!!
I use zinc as that’s what I was given when I started welding. I do however run a spot weld drill in the hole before I plug weld so really I just use it so there is something between the panels
Amazes me how many people contaminate their welds with this stuff because they don't know how to use it!
I used 1 can of the zinc 25 years ago, haven't used it since. Give me clean dry steel. I'll seam seal the weld. Unless you plan on running the weld seam under water, it will last a very long time, I haven't had a rust issue yet. Gene
I'm starting to feel the same way.
They were 95% copper up until 1982...
I have had good luck with this product...
I've been testing the upol weld Tru copper primer. I clean the metal, use a de-greaser and the two coats of the weld thru primer. I'm using a miller spot welder 220v 30amp. I'm getting burn thru on the spot welds. I never had that happen before.
when you spray the weld Tru primer on do you lightly dust it so that some bare metal is still exposed?
I put two coats on but im thinking it was too much. im going to try one coat
Kinda, i don't go heavy on the area where I'm welding.
FWIW, Toyota and Chrysler say not to use it. They want you to treat the seam after assembly.
another option is panel adhesive and using spot welds
here ya go as far as manufactures
and the nays
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