Epoxy Only or Weld through for spot welded panels?

Rusty105

New Member
I am going to be starting my 65 Mustang coupe restoration in a few weeks and I have some questions in regards to how to prep panels that will be "spot welded" with a MIG welder. I have a significant amount of panels that will have the existing spot welds cut out and new panels replaced using the MIG and plug(?) welding the panels together simulating the existing spot welds. A lot of the videos I have watched, and discussions I have seen in forums say to use weld through primer between the panels. SPI Epoxy will be used on the panels, but not sure how to prep the areas nearest the welds. What is the recommendation?

Thanks!!
 

SpencerW

New Member
I would recommend sanding original e coat to bare metal with 80 grit, apply 2 coats SPI Epoxy on your new panels when you get to that point. You do not want any epoxy directly on your spot welds. You will just have major welding problems with contamination trying to weld and the epoxy will also melt during the welding process. I would use copper based weld through primer on your bare metal/spot welds. I would recommend looking at some videos on YouTube: MrFireman164. He has some good videos of epoxy & weld thru primers etc.
 

Rusty105

New Member
I would recommend sanding original e coat to bare metal with 80 grit, apply 2 coats SPI Epoxy on your new panels when you get to that point. You do not want any epoxy directly on your spot welds. You will just have major welding problems with contamination trying to weld and the epoxy will also melt during the welding process. I would use copper based weld through primer on your bare metal/spot welds. I would recommend looking at some videos on YouTube: MrFireman164. He has some good videos of epoxy & weld thru primers etc.
Found his videos......
That Copper stuff is nice. Also looks like flooding the welded pinch seam with epoxy after weldoing is an idea.
 

Chris_Hamilton

Trying to be the best me, I can be
Copper or the standard weld thru is all crap. Adhesion is very poor. You can wipe it off with lacquer thinner. Actually contaminates your weld and makes plug welding more difficult. Minimal corrosion protection benefit. One of those things that I-CAR started recommending in the early 90's and it just gets passed on. I never use it anymore.

Do what "68 advises. Epoxy backside of both panels, drill your holes, fit and then scrape away the epoxy inside the plug weld hole. As good a protection as you are going to be able to get using the plug weld technique. Epoxy front and back of your panels after welding. it'll last another 50+ years.
 

John Long

Member
I agree with Chris. The adhesion with the weld through primer is very poor. I must have done 1000 plug welds on “Precious” while building her and was very impressed with how little the SPI Epoxy burned back from the weld area.

I believe it is far better than the weld through primer

John
 

Cow.kllr

New Member
I normally shoot two coats of un-reduced epoxy primer.
Pre-drill the spot weld holes on the panel and then once in place, I put a small end mill in my cordless drill and clean the epoxy from the spot weld area.
Which one of spi's epoxy do you use for this and can it be brushed on. I want to use it in between panels where they will be spot welded together.
 
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daddio

New Member
On my sons Duster I did just as John did ... took an old drill bit and ground it flat worked great to clean off the epoxy primer in each plug weld ... I stressed over using the weld through primers ... not worth it in my opinion .
 
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