I'm starting to weld up my floor pans and stuff, had a quick question. Is the coating on the steel weld-through, or do I need to grind it off? I've been grinding it down and then coating with a weld-through primer, but wasn't sure if this was a needed step. Thanks!

is it the black coating? usually that is weldable.

Not sure what kind of coating you are talking about, but it can't hurt to get to bare metal & prime. The weld through primer is there to prevent future rusting of the metal you ground clean, but cannot coat after welding (in between layers of metal). And it actually makes your welds a little stronger. Don't grind off more than you need to, leave as much factory coating as you can. If the metal can be primed and painted after the welding, then you don't need the weld through.

I was taught to grind off/clean up the e-coat (the black coating I think Zoso is talking about) and then coat with a THIN layer of weld through primer, only on the bottom layer, where the metal overlapped, when spot welding a panel on top of another. If I was butting a new panel to an old panel, I would grind back the old paint & new ecoat 1" or 2" and stitch weld the seam, no weldthru primer (it would/could be primed & painted after). I never left ecoat along a butt weld, and if I didn't clean up the ecoat around a spot weld hole, the weld would spatter when I hit the edge of the hole.

The stuff I have isn't black. It is some sort of e-coat, my guess is zinc coating. They're WH floor pans and a floor support from Jeff's. It seems to weld OK when I've done practice beads over it, but pops a little more and seems to create a bit more spatter.

Weld through primer has zinc in it, that is what makes your welds stronger. Weld through primer is not as easy/clean to weld as bare metal. I'd prime any metal you can't paint after things are welded together.

Thanks, Gunni. That's the plan, I'm more concerned about whether I need to screw around with grinding down the existing coating before I weld it up. Sounds like might not have to, but probably should.

I don't think it would hurt as long as you protect the cleaned up metal.