My wife and I are disagreeing on this one. We have a 1997 ford f-150 that is getting pretty rusty. My wife is always kicking off the rust making a mess in the driveway. She feels if you remove the active rust it will slow down the spreading of the rust. I feel this is bogus. You kick the rust and this stretches the ''good" metal which causes separation from the paint/primer above it causing moisture to contact the metal and thus causing more rust.
Who is right?
With steel, it really doesn’t matter much. Removing it opens fresh surface for oxidation, but it doesn’t take much to remove a loose oxide like iron rust. Removing the rust will speed rusting slightly, but not by much. If you remove the rust, remove it all and put a good primer on it. A spray can will work just fine.
Kicking off the rust won’t make any difference.
As Neil Young said, “Rust never sleeps.”
Oh no! I cannot tell my wife she is right… Please say “kicking rust off your car is very, very bad.” It will be a long week otherwise. Thanks!
She’s NOT correct when she says this kicking will slow down the spreading of the rust.
For her to help the spreading of rust, she’d have to cut away all the metal that’s infected with rust and make sure all the good metal that’s left is primed and painted so it’s not exposed to air and moisture.
She’s just kicking it because it makes her feel good. She doesn’t like this truck very much, does she?
She is wasting her energy kicking off the rust but maybe she is just doing this to ruin shoes so YOU can take her shoe shopping.
The active rust is still attached to the vehicle doing it’s nasty job. Kicking off the loose stuff is a waste of time.
Your wife is incorrect. If the rust situation is this bad then inspection of the suspension, subframe, and brake lines might be a good idea lest one or all of those parts decide to fall off on their own. 
Just use colored duct tape and she won’t have to kick it off anymore.
If you have enough rust to kick off, you need to get the frame and suspension inspected, something might be rusted enough to be ready to break, with bad results.
Thanks! I will look at the brake lines, suspension and subframe. More importantly, I will tell my wife she is wrong and I am right (kind-of). Sometimes the world is just.