Basic Auto Body Repair: How to Fix Rust Spots

The Greek philosopher Heraclitus said that "the only constant is change". With the pace of modern life, this is pretty obvious to most people. However, most people have a hard time wrapping their head around the fact that everything changes. Over millions of years, mountains are built, erode into the sea, continents shift and weather pattern change. Everything that humans have built will one day disappear. Even nuclear waste, which will certainly be the last evidence of human civilization on earth, will one day disappear.

On the human life span, we see death, degradation and rot around us. Nature is constantly growing and changing but also dying and breaking down. Ashes to ashes, rust to rust. If you have a car that is getting on in years, you'll be familiar with what happens when metal is exposed to the elements for many years: rust. Eventually all metal will rust, crack and breakdown. But if you fight the rust at every turn, you can postpone this eventuality and have a good looking old car, at least until some major mechanical breakdown.

Eventually you will see paint on your car start to bubble and crack. This means that rust has infiltrated the metal of your car and the paint has stopped sticking to the rusty metal.
You may also see holes in the car where rust has eaten through the metal.
Steel wheels also get rusty.
But with a wire brush can look much better.
Start by scraping off all the old flaky rust. A screwdriver does a good job initially.
A wire brush and eventually sandpaper will help clean out the remaining rust.
If you worked at an auto body shop, you'd probably cut out the entire rusted section with a grinder. Rust is difficult to stop once it starts, so if you really want to stop it, you need to remove all the rust and weld in a new piece of metal. This is beyond the ability of most DIY folks. Plus if you're reading this, you're probably trying to postpone rust for a year or two and then will repair the rust again until the car dies or you sell it. If you want to restore an old classic car, look into going the whole nine yards. Otherwise, the quick and easy fix will get the job done quickly and cheaply and will keep moisture away from the rust preventing it from spreading. You're basically just postponing the inevitable, but thats the goal!

Another good idea is to use a rust enzyme. This is chemical available at auto parts stores that converts the rust into benign compounds. Although you will be sealing the rust from the elements, you don't want the rust to spread under paint and bubble up prematurely.
You fill the holes and gaps in the body of the car with something called "Bondo". This is a fiberglass puddy that you can buy at auto parts stores. You mix hardener into a gray putty and spread it into the hole. The Bondo will harden quickly so mix it in small batches.
Try and spread the Bondo evenly and smoothly. This will make it easier to sand smoothly once it hardens.
Start with rough sandpaper and work you way to smoother grits. Get the Bondo as smooth as possible. Focus on where the Bondo meets the paint.
Keep it as smooth you can. When you paint it, imperfections will become apparent.
Wipe the area with a damp cloth to remove the dust. Then tape newspaper to the car around the area you are repairing. This will catch paint over spray and keep it off other parts of the car.

Next apply auto body primer. This comes in a spray paint can. Put on two or three light coats as per the instruction on the can. This will act as an added layer of protection preventing the rust from starting again.

With the primer dry, apply the paint. Your local auto parts store will have spray paint for most makes and models of cars. You may also want to put on a clear coat which will make the area blend with the rest of the car.
As you cans see, this repair job is certainly not perfect. If you have a fancy or antique car then you probably want to take it to a professional. But if you have a car worth a few thousand dollars, it makes a lot more sense to spend $25 and fix rust spots by yourself than paying an auto body shop hundreds of dollars. It may not look as nice or last as long, but it will keep out the elements, prevent the rust from spreading, looks better than rust and is a cheap fix!
Eventually this car will die and will be sold for scrap. But stalling the advance of rust will ensure that the car will look good until that happens.