how to use weld-thru primer Options

[jmitro]

two questions about using weld thru primer, (assuming that proper usage is spraying primer on the backside of two adjoining pieces so that primer covers the bare metal that cannot be accessed once welding is completed);

1. Do you change the weld settings on the welder? It welds terribly with poor penetration. Or do you grind off the primer from the anticipated weld spot? If so, then it's defeating the purpose of weld-thru primer, is it not? it leaves bare metal.

2. After welding is complete, do you grind off the exposed weld-thru primer and replace it with POR-15 or primer of choice?

[Jeff Hail]

The best method is to coat both pieces that face each other that you are welding. Scratch, grind , sand a small margin to bare metal where the nugget is going to land. I also clean the area on the back side of the punched or drilled hole. Good clean metal to metal contact.

1) First think clean welds.
2) If you are seeing green flashes of arc light you were born in the 60's or 70's, did not have a clean weld zone and are burning zinc up. It looks bitch'n but its really a stellar way to contaminate welds.
3) The cleaned nugget zone should be a little larger than the pilot hole. I normally clean about a dime size area to get good cut into the lower panel.

Zinc and or copper weld sprays melt at very low temperature. The concept is to have a clean weld and let the weld spray just melt around the weld area.

Welding through a dissimilar metal to join two similar materials well would be like strippers sitting on your lap because you think they actually like you. The word "Strippering" originated from that false belief from sugar baby hell that $2 buys a nut and also applies to many things in life including welding. Don't do it, its a trap!

Everything cools down and the weld spray makes a metallic seal around the weld zone theoretically encapsulating it. The second life of weld sprays to is to provide a sacrificial coating between the joined panels to retard corrosion . Zinc or copper will oxidize much slower than steel buying time as a barrier by chemical reaction.

A few good tips: You don't need two or three heavy coats. One even coat is fine.
Zinc is pretty much heavy metal so use adequate ventilation or push the fumes away with a slow speed fan. Green arcing is not so good, the weld is stopping and starting by resistance while contaminating itself. White crud on your welds that looks porous is exactly that.