Rust from MIG welding

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Hey gents,Since starting out MIG welding this summer I've noticed that my welds wind up rusting almost right away. Lets say I'm going to weld an enclosed area like a car body panel (not that I would attempt this myself). Since you would be welding a patch in place, and cannot get to the backside of the joint after the welding is complete, wouldn't it begin rusting back there?  How is this prevented or done properly?-Ken
Reply:Weld through primer is what your looking for.(Home)Miller Maxstar 152 (sold)MM211/spool gunLincoln AC 225C(Work)Dynasty 350Powcon 300STLincoln SP-175TWeldlodgic AWS150sWeldlodgic AWS300Custom Resistance seam weldersCambridge Vacuum EB weldersI smell something burning.
Reply:Is that what the factory uses on the backside of body panels?
Reply:There is always a way to get to the back side of everything either with a spray gun or a wand. I don't like welding in patch panels on cars I want to last. I try to replace whole panels and use spot welds and seam sealer.
Reply:Let's see....Nice clean steel to weld to, filler that was molten. Yes, welds do rust very quickly.  That's why I apply primer to the both sides of the HAZ while it is still warm to the touch. And paint before the welded item is exposed to the elements.Be wary of The Numbers: Figures don't lie,. but liars can figure.Welders:2008 Lincoln 140 GMAW&FCAW2012 HF 165 'toy' GTAW&SMAW1970's Cobbled together O/A
Reply:Originally Posted by mike837goLet's see.... That's why I apply primer to the both sides of the HAZ while it is still warm to the touch. And paint before the welded item is exposed to the elements.