Treatment of Rust Patch

Maybe have a body shop or mechanic friend (if possible) inspect the whole car. With the age and location (lots of road salt?), that might be the proverbial tip-of-the-iceberg. Suspension components on the underside are very rust-prone too. What's the miles on it?

Salt: Good for Roads, Bad for Ecosystems? – Susquehanna University.

 

Your profile like money doesn't state where you are I'm guessing you're where rust is and happen salt on the roads etc New York whatever so this is just going to be reappearing every few years unless you can keep your car in a nice temperature controlled garage and off the streets in the winter and so on and so on then what's the point of having it looks like front fenders those are like $70 a piece if that and some markets so you wouldn't waste time with the body shop or with somebody sanding and grinding on that front fender there's no meat there Time you hit it with the grinder you're through it You buy new front fenders yep now you got to have them painted or something then in 3 years probably in the rust areas where you may or may not live now this will be back how does the rear quarters look That's what you need to be looking at or is this a vehicle that's just been down at the beach? I wouldn't worry about it leave it alone but if it's a must replace the front fenders

 

How long have you owned this vehicle?

As others have said, it needs to be inspected from below.

The other side of that fender could be very rusty. If you will be doing this yourself, and it is just that one finder, you might want to take it off the car to do the work. Remove the fender liner (buy replacement clips ahead of time, most of them will break), then unbolt the fender. At that point you have two choices, bolt on a replacement fender in the same color from a junk yard, probably around $100, or clean, derust, and paint. The first choice is far and away the easiest, and if your time is worth anything, the least expensive.

If you must reuse the fender, knock off the loose rust with a wire brush, sand down to a light layer of rust, spray with rust converter/primer (it comes in spray cans, don't get it on you, really don't get it in your eyes or breather it), then paint. Painting part of a panel is never going to look good though. Did I mention replacing the fender is a better choice? A body shop could do this for you, but who knows what that would cost.

 

Pulling out the "protective" plastic wheel well liners, you'll likely find a mess of leaves and mud.

 

You've pretty much got it.

Touching up your list to how I would do it:

- Sand down as much as possible with a wire brush, but don't be afraid to use coarse sandpaper or or even a pick or a file if needed.
- clean thoroughly with alcohol/solvent/paint reducer, let dry
- Apply rust converter, let dry
- clean thoroughly with alcohol/solvent/paint reducer, let dry
- Apply automotive primer; two coats+
- wet-sand primer. You don't have to go crazy, one quick pass at 400 grit (again, while wet!) should do the trick.
- clean thoroughly with alcohol, let dry
- Paint: at least one coat of automotive color coat, you can use the generic Dupli-color rattlecans. The color will be close but probably not precise.
-vinyl cover

So the shopping list should be a small bottle of rust converter, a quart of paint reducer, solvent or high-percentage rubbing alcohol, one rattlecan of auto primer, one rattlecan of color coat, clean cotton rags, 400-grit autobody wet sandpaper <a piece of vinyl> a roll of tape and some paper for masking.

Good luck!

 

Plus labor. If a matching color replacement fender is available locally for pickup it might well be cheaper than even just that list of supplies.

But again, we are ahead of ourselves. The car needs to be inspected from underneath. Not much point in fixing the fender if some major structural component is so rusted through that it isn't safe.

 

The availability of a clean rust-free fender and the thought of simply unbolting the old one are... how should I put it?

How about, 'Heavily localized to Southern California?'

Valid technique out there, but if the car has enough rust to put a hole in the fender, you can bet that each and every (metal) fastener is going to take substantial time to remove, and each one may require a different method of attack, and they may all need to be replaced much like the plastic fasteners for the liner. And this counts for both the donor and the recipient.

It's probable that there is significant rust elsewhere on the car and that it may have real safety issues, but I think that is beyond the scope of this discussion. OP wants to fix one rust hole and pass inspection afterwards.

 

Understood. I would expect here that both the fender and all of its (metal) fasteners would be fine.

Unpainted fenders are $47 at RockAuto. Rattle can paint one of those and install it. The color probably won't match perfectly, but easier to get a uniform and smooth surface. The issues with the fasteners don't go away though.