Weld Thru Primer.....Doesn't!

In article , Dennis van Dam wrote:
I believe it is meant for Stick welding or Dual-shield, both or which have a hotter arc and better cleaning than MIG.
MIG really likes clean new metal. Stick and dual-shield are much more forgiving about surface coatings.

I find that the primer gives trouble if it is put on too thick. The idea of a primer is that a second coat will be put on later. That is an awful lot of welding for something only 1/8th thick.I imagine you would have gotten a lot of distortion unless you were running cold??? Randy

The zinc 'weld through' primers arn't great with a process that doesn't tolerate dirty metal. Some stick electrodes are fine with it, but any time you'd need to remove alvanizing, the zinc primers need to come off.
There are non-zinc coatings that are a lot better, but generally not intended as primers, more as preweld protection. They can work well for protecting areas that won't be painted.

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What brand of primer did you use? I've used 3M's product and DupliColor's product, and found the 3M one to work reasonably well with MIG. I was primarily welding 18 gauge sheet, but I did a small amount of 1/8" hot rolled with it as well. The DupliColor product, on the other hand, was crap. It caused massive amounts of spattering and popping, and would have been better left in the can. There were some pretty noticeable differences between the two aside from that. The 3M one went on much more smoothly, and smelled as though it had some carefully picked chemicals in it. The DupliColor stuff seemed like it was just some altered formulation of primer and not much else. I'd use the 3M stuff again, as it seemed like it worked as intended and didn't gunk up my welds.
Eastwood sells a product called Bloxide that is supposedly aluminum based instead of zinc, I don't know if that'd work better or not. I'll have to give it a shot someday and see. Until then I'll keep using the 3M one when I need such a thing, although I do think it's probably best to clean up the actual point of the weld a bit with a brush just the same. The primer seems more for use on the backside of the welded material, like body panels you can't paint after assembly. In fact that's how I use it now, I just spray the backs and leave the front clean. The exposed portions will get cleaned, primered, and painted later anyhow.

. . I've used it. It is from Tempil (the heat stick people) and works well. Not intended as a primer so much as a protective preweld coating. I'v painted over it with, and it works. Welds through fine.

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Ernie Leimkuhler wrote:
Thanks Ernie.
I've been welding for over a decade but I don't weld every day and sometimes I have to relearn basic, albeit nuance, lessons such as MIG welding being more appreciative of clean metal than stick welding is. However I did not know that a stick welding arc was typically hotter than a MIG arc so I did learn something new as well.
"Randy Zimmerman" wrote:
Randy,
Applying the primer more sparingly did occur to me but in the moment I was sufficiently frustrated with the problem that I just removed the primer altogether and went with bare metal. The next time I have occasion to use weld thru primer I'll definately favour a lighter application.
Your right, welding a flat strip to a flat strip the way I described, would distort for sure. My description was over simplified to keep my question (relatively) brief and to the point.
Actually it's a series of 1/8" strips of steel being applied to the faces of an existing steel rectangular tube to repair rust damage to the tube by building up a new tube around the old tube. This is still an over simplification of the process but you can see that as a built up box instead of just independant flat strips distortion is less likely. As well the welding sequence was executed (very) strategically, to avoid undue stresses and attendant distortions, and in several instances such as when the weld seams primary purpose was not so much structural as to seal the corners of the box, as you suggest, I did run cold.
enl snipped-for-privacy@yahoo.com (e) wrote:
Thanks. You and Ernie concur on this. I was mostly interested in post weld protection in an area that was not going to be painted any further so maybe one of these non-zinc coatings would have worked better. However to further acknowlege what both you and Ernie have stipulated, probably any thing that gets between the metal and the MIG arc is likely a detriment to the MIG process.
The Hurdy Gurdy Man wrote:
Interesting question, that.
In the absence of actual technical expertise (in this case chemistry) or extensive (read expensive) practical experience, it's always a total guess as to how effective a 49 cent bottle of magic mystery potion is going to perform compared to a $4.99 bottle of magic mystery potion. Since the cheapest aerosol can of this stuff was $13 US I decided to take a chance and start with the cheapest. The end result was going to be completely hidden from view anyway. This was Mar-Hyde brand weld thru primer. Of course one can wasn't enough so when I went back to the auto body supply store and discovered a sale on another brand ($10 US) I picked up a couple of cans of "Dominions Sure Seal LTD" Hi-Build Zinc Weld Thru primer/coating cold galvanizing compound to finish the job. I'm not really able to say that one might have caused more or less of a problem than the other, just that by and large it wasn't working out, particularly in the plug welds (even after wire brushing the primer out of the bottom of the plug weld hole before setting the plug weld).
I've used 3M's product and DupliColor's They had 3M's product but that was *** $18 US *** a can. If it's true you get what you pay for than maybe I should have gone the high road and gotten the 3M. (But that would have cost me $54 for complete coverage, a bit steep for this project.)
I was Thanks for the reply Hurdy Gurdy Man, I'll keep the 3M in mind for future applications where the expense is warranted.
Thanks to the rest of you as well,
Dennis van Dam