In order to properly treat fill and prep the fender just follow these easy steps.
How to repair pitted sheet metal.
Sand the area again with a fine grit sand paper to.
Using a filling primer would probably result in still being able to see the pits to a certain extent.
Wrap a sheet of 80 grit sandpaper around a sanding block and sand the pitted area aggressively.
The sand paper can be held in your hand for smaller.
You can use a.
Then paint it with fiberglass resin like you use to glass stuff only without the cloth then give it a skim coat of mud or bondo or whatever they call it where you are from.
Assuming that your metal is still strong enough i would use a polyester sot putty which is basically a very fine grained body filler that is slightly easier to sand.
If the area is heavily rusted and pitted and wire brushing by hand is ineffective use a drill with a wire wheel photo 2 and a primer that adheres to rusted surfaces such as krylon rust tough or rust oleum.
How to fix pitting in metal before painting clean.
Work outward and then return as you remove the pitting from the metal.
Mix the correct ratio of two part auto body repair filler and hardener as determined by the product.
Grind down heavily rusted metal spots faster with a wire wheel and a drill or angle grinder.
Attach the wire brush to the drill and apply to the metal.
Apply eastwood fast etch to the area with the rust pits.
Give it a serious cleaning mayhaps some naval jelly or some other type of rust remover.
Fast etch eats into the rust dissolving it and leaving clean metal behind.
Sand the area with a coarse grit sand paper using a circular motion.
Moved over to the passing lane.
Cover the area with plastic wrap to prevent the fast etch from evaporating before it can work.
The electrolytic bath gets things cleanest a chem rust converter is a good idea to insure it s clean then filler is the only way to get it smooth sand blasting is good but even that will sometimes leave oxide in deep pits so the converter is still useful.