Step by Step Rust Repair

I'd been restoring my 67 Mustang coupe when I ran into some rust issues. Surprise! The car was actually very solid with barely any rust to speak of but the original fenders had more wrinkles than an assisted living home and they needed to be replaced.

Rather than buying reproduction fenders of dubious quality, I picked up a pair of factory fenders from a guy on ebay. For 150.00 I thought I had found the deal of the century, but it turned out the cost of shipping was going to be 3 times what I paid for the fenders themselves. Fortunately the guy was eventually heading south for a show so I waited a few weeks, he brought them along and we met halfway.

Obviously, 2 fenders for 150.00 bucks means they will probably need some work. And they did. All in all, they weren't too bad. They were straight but one had rust at the top of the fender rather than down low where they usually get rusty. Fortunately, my original fenders could provide good patch panels so I decided to fix them myself and document the effort. Here's what the rust looked like on the replacement fender




I scribed a straight line from the front of the fender to the side with the inner fender well. Using the line as a guide, I made the cut with the cutting wheel taking care to remove only as much of the fender as was needed. I also had to drill out the spot welds where the fender is welded to the headlight bucket.



Once the spot welds were drilled, I was able to remove the cancerous metal and clean up the surface rust on the headlight bucket.



I used the rusty piece as a template and placed it over the original fender. I repeated the same steps on this fender as well taking into account the width of the cutting wheel.



The fun part starts next. You need to take a metal file and slowly trim up the patch until you get it to fit well. File and test fit, file and test fit. Go slow since you can always take more off but it's harder to put metal back.



Due to where this rust was located, I had to test fit the headlight bucket as well to make sure everything lined up, including the hood.


Once I was happy with the fit, I sanded off the paint from the patch and started tack welding the patch to the fender. Only tack a couple of places, then test fit EVERYTHING. Test the fit numerous times to be certain of placement before you start putting lots of tack welds down. Also, NEVER lay down a continuous weld. This will warp the metal due to the heat. Tack welds work best.







Once you get the tack welds done, test fit again and start grinding down the welds.


I've talked to a couple of body and paint guys since I did this and they said that I probably should have primered the fender first and then laid down the Bondo. I mention this so you don't make the same mistake I did. Fortunately, this fender has now been painted for over 5 years and nothing is popping out (knock on wood).



I finished the Bondo with some 800 grit paper and a long board checking to make sure everything transitioned well then I shot the fender with some 2k primer. I didnt have any scratches using 800 but you may want to use a finer grade of paper when finsihing the bondo. High build primer helped me fill in the scratches.





That's it. If you're patient you can do it too. Hope you find this info informative.

Nice post, good work too!

Originally Posted by iryshman

Hope you find this info informative.

Yeah I did. I'm about to do the same thing but I'll be replacing about 90% of the quarter panel. I will be keeping the quarter extension.
Thanks for the primer/bondo tip.

nice work. I wanted to ask for clarification on the last comment about the primer then bondo. Can I assume that your body shop buddies suggest epoxy primer first then the bondo then the high build 2k. That seems to be the current standard from the paint mfg companies. Thanks for a nice illustration.


Bill

Originally Posted by bonfire

nice work. I wanted to ask for clarification on the last comment about the primer then bondo. Can I assume that your body shop buddies suggest epoxy primer first then the bondo then the high build 2k. That seems to be the current standard from the paint mfg companies. Thanks for a nice illustration.


Bill

I suppose the paint system that you use could make a difference overall and you might want to talk with the guys you buy your supplies from but in this case my buddies said I should have simply used a good self etching primer over the entire fender first, let it cure, scuffed it with a scuff pad, cleaned it and then applied the Bondo. Then you squirt the high build 2k, let that dry out and shoot a guide coat for finding the high and low spots. THEN you knock years off your life by sanding and sanding and sanding.

I'm not a paint expert by any stretch but I've been told over and over by many different people who are in the auto body/paint business... One thing you should always do is use the same paint manufacturer, or "paint system" for your paint supplies. That way you minimize the chances of running into incompatibilities between primers, sealers and paints that can cause paint failures.

Today's paint compatibilities are much better than back in the days of Lacquer & stuff, but I too stay away from "other" brands when doing a known job.

About the Bondo on the vehicle.

I ALWAY'S put my bondo on the metal only, but only because I'm "special" like that...

Bondo is like a really kickass glue, if you scratch the paint and bondo it the bondo will stay until the paint comes off.

The surface you want to apply bondo to is just better if it's consistantly paint free. That way the "hold" the bondo has is identical across the job, therefore more reliable overall.

Rust CANNOT build up under Bondo unledd there is a hole that oxygen and moisture can get into.

No holes ='s NO Rust EVER. It simply cannot happen. So, bondo what you want as long as the elements are NOT able to get to it. It's EXACTLY the same reason we paint cars, it keeps the elements from getting to the METAL, which is the foundation and the reason behind our cars being what they are.


FE

Since I am a beginner when it comes to bodywork, I have been reading everything I can on body repairs and prepping for paint. I found your write-up very informative especially since you added very clear pictures to support your descriptions. Thank you.

after welding any patches especially- suggest 'ospho'/metalprep treating the steel before priming- if theres weld, theres likely at least tiny gaps to allow moisture in from the inside/backside... etching will add extra insurance against corrosion. metalprep leaves a almost invisible phosphate coating(metal just a tad more gray) that will protect the metal a little bit- but more importantly, convert any microscopic oxides into iron phosphate- bare metal will *begin* to oxidize as soon as air hits it- might not see the rust, but its starting. phosphate etch stops the process in its tracks.

A guy at work showed me this stuff years ago- sanded a piece of sheetmetal, wiped one side with ospho, rinsed it off and sat it outside- next day the untreated side was orange. a month later the treated side was just barely beginning to get some streaks...it really works.

Hi Guy

Really a beautiful job on the front light fender patch job you did.

I'm getting ready (hopefully with your help) to repair my lower R/H fender on
my '66 Mustang Convert.

Question(s) Please:

1. Have you ever used CLECO FASTENERS?
2. If so, do you recommend 'em for the lower R/H fender repair I going to do?

I got the patch panel and inner brace to do the job.
What's the best way to LINE IT UP ?
I don't want to; OVER-LAP THE JOINT, what do you suggest ?

Thank You
GOD BLESS

Schooner

That was great write-up and the results were awesome. I wish I could weld. I was pretty good with a stick welder when I was in high school but that was a long tine ago.

But I too have been doing my own body work for ever and I put the Bondo right on the bare metal after a good roughing up and a wash with denatured alcohol. I have heard the pros and cons of doing it this way but it really boils down to personal preference and your point of view.

Later!
Mr. Ed