Debate: Do you sand down to bare metal on every rust repair or just treat the surface?

I was fixing a spot on a 2012 Ford F-150 in my shop over in Springfield last month. Did my usual grind and fill routine, but six weeks later the rust is already showing through around the edges. Now I'm wondering if I should have taken it all the way down to clean metal even though it would have taken twice as long. What's your cutoff point for going all the way down vs. just treating what you see?

2 comments

2 Comments

paulw8715d ago

Bare metal every single time, no exceptions. The thing most people skip is checking the backside of the panel after you grind it down. Even if the front looks clean, moisture can be trapped behind the metal and eat through from the inside out a few weeks later. That's why your repair came back so fast, you probably had hidden corrosion working its way from the back. I always drill a small access hole or use a borescope to peek behind before I even pick up the grinder. Saves a ton of headache later. Sanding to bare metal isn't just about what you see, it's about making sure the whole area is actually dry and solid.

rowanellis15d agoMost Upvoted

Gotta call a small thing out there, drilling a hole just to check behind a panel can actually create its own rust problem if you don't seal it back up proper. Why introduce a fresh spot for water to get in when you could just look at the backside from the other side of the panel or through an existing seam?