Hot Rods Weld tru primer on rear 1/4 panel skin and pillars?

When replacing a the outerskin do you apply weld thru primer on the pillars? If bare metal is left what will be the result?

 

Rust

 

You only need weld through primer in lap/pinch weld type joints. In the HAZ. Where regular automotive paint type products will burn off. And, you have no access after welding to apply them. They also need to be throughly removed from any surfaces to be painted afterwards.

 

The term "Weld Through Primer" is a misnomer. In the Autobody world, Weld Through Primer must be removed from all welding site(s). If not removed from the actual welding site, the weld will be contaminated. All remaining Weld Through Primer will corrosion protect the bare metal adjacent to the welding site(s).

VR&C.

 

Why is no one using the newer structural adhesives , instead of welding lapped joints

 

I wouldn’t do either. No glue, and no lapping joints. Well, I might lap a joint on a body subrail or that kind of location. But never on outside skins.

 

What do you mean by HAZ?
Also why must weld tru primer be removed before paint? Can I put epoxy primer or filer over weld tru primer?

 

HAZ= Heat affected zone and no. Epoxy over clean bare properly prepared metal. Some fillers can go over bare metal or over epoxy. Each has drawbacks. You need compatible materials and follow the data sheets.

 

when lapping weld joints , as in pinch seams , plug welds ,, i allways use a COPPER based weld thru primer where the spots are , like UPOL or similar ,, it conducts electricity better and the silver colored ones are zinc based and produce bad news when welding ,, after clamping and all the planets are lined up I will take a scribe and " scratch out the hole" before welding makes for a better starting arc and welding .. i tig everything and give the pedal a lil flash at the end to flatten the plug and look factory ,,, with a mig you can use more heat than you normally would and be fast and will produce a flatter spot with less finishing required ,,, Remember allways make practice welds on the bench first!!!
fabricator john
miss you dad

 

I don’t because the joints in old cars weren’t designed for glue. Many like roof skins are very narrow.
Modern cars have a lot more structure than older cars. The suggestions on a 3m glue are not repair procedures. A replacement panel on a new car can be glued in places but welded/rivet bonded in others depending on manufacturer.

 

I only use weld thru on a welded seam. The backsides of new panels get primed. The original structure behind the panels are usually rusty so they get some kind of rust treatment