Rusting or corrosion is one of the worst things that can happen to your car. In fact, it can be more damaging than you think. It won't just deprive your car of that grace, but will also bring about a whole lot of performance issues, such that even selling it will become difficult.
Rusting is a natural process which cannot be totally eliminated. However, there do exist some measures of preventing it and some methods of repairing it. By repairing the rusted area, you can make your car look as good as new. The earlier you find these spots, the easier it will be to fix them. So you need to keep an eye for them.
If you don't have a grinder, you can use a coarse sandpaper or a sturdy wire brush to remove it. You will have to make the surface smooth and leveled by scraping away the traces of rust or lose paint. You may have to use rust removing solvent to ensure that even the last traces of rust are eliminated.
Using a sandpaper, work your way around the rusted area till you reach the area which is not affected by rust. Wipe it clean with some cloth. No specks of dust should remain on the affected area when you do the final touch up.
Once you are done with this part, cover the surrounding area with tape to ensure that you don't mess up the color in the unaffected areas when you are fixing it. Apply a smooth layer of glazing putty to the cleaned area in order to fix the scratches, if any.
Once it dries, take a good quality auto primer and apply three coats of the same on the affected area. Make sure that you give some time for each coat to dry before applying the next coat. After the third coat, allow the primer to dry overnight.
Once it's dry, you can apply fresh coats of paint using a spray gun. Apply 2 - 3 coats of the same, but only if you find the paint matching the entire body. If not, stick to a single coat of paint which would give it a light touch. Allow this to dry overnight. Once the paint is completely dry you can use car wax to give the surface a glossy finish.
The foremost thing would be to tape the surface areas around the rust hole so that you don't harm the finish of your car while repairing them. Trim the edges and remove the debris in the affected area. Use a grinder or sandpaper to remove the rust and smoothen the surface.
Once you have a clear surface, take a hammer and tap the edges towards the car interior. Take a sheet of metal and cut it to a size slightly shorter than the actual hole. Apply roofing tar sealant over the edges of the metal cut out as well as the edges of the rust hole.
Wait for some time and place the metal sheet into the hole, sticking the edges with the sealant together. Allow it to dry overnight, so that it becomes firm. Once you are done with this, you can follow the normal procedure of applying the primer and paint as mentioned.
Like we said earlier, it is possible to prevent car rust, which can be done by resorting to simple prevention measures, like applying rustproofing material or car wax once in a while. Car is an expensive investment. When you have already made this investment, you should make it a point to devote some time for its maintenance.