Weld thru primer doesn't seem to work at all

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PostPosted: Tue Aug 07, 2018 8:07 pm
Am I using this stuff incorrectly?

From what I know, or what I think I know, it's supposed to be used in between lapping panels and not exactly for welding straight on. So lets say I have two pieces of sheet metal and one of them has holes in it so I can plug weld them to mimic the factories spot welds.....in that case I would spray weld through primer on the back side of the panel with the holes drilled and then on the panel behind that the plug weld puddle is going to form on.

Now what I do is after I mate the panels together, I clean the weld thru primer out of the holes so I'm welding on clean metal with the only weld through primer being in between the panels and essentially unseen to the eye.

Problem is that the welder reacts to it as if it's trying to weld on regular paint or unclean metal. As soon as the puddle starts to touch the outer edges of the plug weld hole, it starts popping and boogering up all over the place. It's basically impossible for me to use this stuff because I end up having to weld, grind, weld, grind, weld, grind until I get it filled in on the 4th try. Any idea whats up here? I've gotten the same results with SEM Copperweld and SEM Weld Thru.



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PostPosted: Wed Aug 08, 2018 11:16 am
I had the same experience with another brand I bought at my local Welding supply store.
I had cleaned both sides of the metal clean as well and just applied the weld through primer I don't know what the problem was other than my welder the wire or the Gas mix I was using something didn't like the stuff that's for sure.

Others here have used different brands with good success 3M makes one and they show it being used in several training videos as well with good success.
I have since purchased another brand but haven't tried it yet.
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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PostPosted: Thu Aug 09, 2018 9:52 am
I had similar issues when trying to use this stuff. Ended up just using a quality epoxy primer and cleaning just the spots I planned to weld to bare metal. Where I had access I then covered the backside of the weld with more epoxy.
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PostPosted: Thu Aug 09, 2018 8:35 pm
Sounds like I'm not the only one who hasn't had any luck.

Funny thing is I was watching Graveyard Carz just last night and they were installing a trunk pan into a Demon. The guy showed all the holes drilled into the pan that they were going to use to weld to the frame and they were all covered in weld thru primer. He spent a few minutes talking about how weld thru primer is great because it flows into the weld and essentially helps seal it from outside contaminants after the weld is done. It didn't seem like a commercial for anything because he didn't talk about any specific brands or whatnot.

Then after the commercial break when they go to install the trunk pan, there's no more weld thru primer anywhere on the pan. It was just ground down to bare metal around the plug weld holes lol.



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PostPosted: Tue Aug 14, 2018 7:57 am
I found another product to use after welding

https://www.3m.com/3M/en_US/collision-r ... -wax-plus/

I havn't tried it yet but it does look interesting.
Dennis Barnett
A&P Mechanic, FCC General radio Telephone Operator
Line Maintenance A&P Mechanic and MOC Tech specialist.

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