Is there any accurate way to tell whether steel is coated or plated with something. I grind the weld area for good measure anyway, but would like info on determining the content on scrap material. Is the only real way to buy it new with the info still stencilled on it? I got some 18 gauge steel the other day and thought it was just mild steel. It would not weld worth crap, so I just quit welding it. When I looked at the surface with a magnifier I noticed it had a pebble finish as if were possibly dip or spray coated. I keep ventilation while I'm welding, but would rather just not strike any arcs to coated or plated steel. I've also heard that grinding never really gets all of the coating off ,and can contaminate sanding or grinding wheels so they contaminate other welds when used again. I'm referring to light mig welding with 75/25 gas. Any info greatly appreciated.