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Weld thru primer doesn't seem to work at all

PostPosted: Tue Aug 07, 2018 8:07 pm
by ESP47
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 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.

Re: Weld thru primer doesn't seem to work at all

PostPosted: Wed Aug 08, 2018 11:16 am
by Doright
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.

Re: Weld thru primer doesn't seem to work at all

PostPosted: Thu Aug 09, 2018 9:52 am
by '68 Coronet R/T
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.

Re: Weld thru primer doesn't seem to work at all

PostPosted: Thu Aug 09, 2018 8:35 pm
by ESP47
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.

Re: Weld thru primer doesn't seem to work at all

PostPosted: Tue Aug 14, 2018 7:57 am
by Doright
I found another product to use after welding ... -wax-plus/

I havn't tried it yet but it does look interesting.

Re: Weld thru primer doesn't seem to work at all

PostPosted: Tue Oct 30, 2018 10:45 am
by tperazzo
I use Like 90 with some success. Don't put it on too thick and I still scratch out the hole the center hole in a plug weld. Its a bit pricey, but works way better than others I've tried.

Here's a video also of simulated spot welds:

Re: Weld thru primer doesn't seem to work at all

PostPosted: Sat Dec 08, 2018 7:45 pm
by noelc
Sometimes late is better then never.
I was told this by an expert on late and never, so as second hand information...grain of salt kind of thing.

The reason why you guys are having this problem is more complicated then you realize.
One is the welding process. It's the complicated one.
Two is the purpose and application of the product.
And three is...probably because standing on one leg with your eyes closed touching your nose and counting to ten is impossible. Try it and you'll see. Welding is about the same. But your doing it with a weld thru primer. That's like the added pressure of doing the one leg thing on the side of the road with the cop as your witness to the effort.

One...While the welding power source does make a difference it's more the operator, his parameters, the out put and settings make the difference in the wire melting. ER70S-6. ER70s-2 ? Deoxidizers and puddle fluidity differences.
What size are you using? .023,.025,.030,.035? It makes a difference. Think of that wire diameter as a gun shooting bullets. Is the bullet the same size as the barrel or had it gotten bigger before it shorts off? How much powder propels the bullet?

You may not appreciate it as such, but it's a droplet, how wet has it become? What causes the wetness? Voltage. Or less wire fed speed? Shorter arc lengths? It's complicated, or it easy. Depends how much you think about it or how you see it sticking metal together.

Those weld thru primers are zinc based. Any appearance of or traces left behind will burn off, in the proper welding conditions, but, in turning that zinc to vapour you create a very ugly environment for the welding arc. That's why product formulations with a heavy solid require being well shaken into solution before applying. Well shaken. You don't want those zinc flakes heavy on the surface. The pressure of zinc vaporization is a pressure acting on the arc, and a repelling act against the droplet formation/ metal being deposited.

Here's some why. All that stuff does is from the heat of welding repel what isn't burnt off, as the weld cool it's drawn back in to encapsulate the spot weld or plug weld created. With out proper welding considerations, IMO, the tendency to over heat through welding is so much so, the heat effected zone changes, zones of the zone become wider, more zinc gets burnt away as a result, the HSLA steel is changed well past the narrow heat effected zone expected. That being the case, which is the lessor of the two evils when it comes to structural integrity? A weakness to the metal or the risk of corrosion?

Now, it's not all gloom and doom. Don't over use the product. Your not painting although you are required to provide coverage. ... -05917.pdf

3m says 1mm on each surface. The reason your doing such an application has to do with corrosion resistance in modern steels, the reaction to those metals from heating and cooling through welding, and in the case of HSLA steels, how heating and cooling in the Heat Effected Zone has changed mechanical and chemical properties, tensile strength loss with increased loss to corrosion protection in these areas. How much so depends however on the heat applied when welding?

So does shielding gas being used play a roll? Yes. CO2, 75/25? I didn't mention nozzle size but it to plays a roll.
Look at CO2...It comes out and releases energy hitting the plate. Arc plasma stuff. Wide and not as deep.
Mixed gas...heats the center and more radiant on the out sides. Deeper in the middle, not as wide. The end of the wire is melting in this.
What they do however is effect the squeeze and pinching of droplets off the wire end. Another way to think of it causing problems in filling plug welds with weld thru primer, is the efficiency electrical current flows through the gas. You could think of seeing through fog. Orientation and direction is effected.
Think of it this way, if you had x amount of gun powder, are you better off with a bunch of little bullets or a few big ones? The gas effects parameters to strip droplets, with Voltage and WFS requirements in this consideration of performance.

As well voltage, wire feed speed, nozzle size and stick out. That and believe it or not, how you weld the hole shut. ... -05917.pdf

My pictures don't show any weld thru. That's because I didn't have any to use at the time. Normally I would have sprayed some down just as a bit of rust protection on the lapping surfaces. In new car construction it's part and parcel with proper repair procedures. This isn't such a repair.

If I had applied it, I would have scrapped the holes free and with a fresh cut end to the wire, struck the arc on the top overlapped edge, walked in and down, quick loop around and finished in the center. Higher voltages, WES, longer stick out to narrow the arc width and move steadily but quick to plug the hole. Some will do it differently. Smaller hole, fresh cut wire, a hot burst in the center with plastic flow creating fused edges. Different strokes, smaller circle to encompass.

Hopefully I've added something to the conversation? From a welding perspective, it's still crap to weld through. :knockout:

Re: Weld thru primer doesn't seem to work at all

PostPosted: Tue Dec 10, 2019 6:01 pm
by Warthog5
This Vid sold me on Upol Copper.....It is aprox $33 a can online....I bought 2 cans in prep for a project

Re: Weld thru primer doesn't seem to work at all

PostPosted: Sun Apr 26, 2020 8:18 am
by chipjumper
Warthog5 wrote:This Vid sold me on Upol Copper.....It is aprox $33 a can online....I bought 2 cans in prep for a project

To summarize the video,
The copper type weld-thru primer will theoretically survive the extreme working temperature of welding sheet metal. The zinc style will boil away and not protect the heated area.
Temperatures presented in the video:
Welding low-carbon steel approximate melting point (weld) 2600-2800 F
Melting point of Zinc: 787 F
Boiling point of Zinc: 1670 F
Melting point of Copper: 1983 F
Boiling point of Copper: 4667 F

I'm going to do some rockers and cab corners soon and I'm going to try out a copper based weld-thru primer.