Refinishing back side of fender question...

[BrewSTL]

Decided while stripping the paint off of my car that my easiest approach for some spots, and to do some things right, that id pull my fenders.  To me they still seem salvageable.  There is surface rust on the back side of the fender, which seems more than fair.  But my question is for anyone who has pulled and restored their fenders and was in my same situation.  What did you do to surface prep the back side of the fender?  I have ospho, and felt that might be a good solution to neutralize the surface rust.  But I’m under the impression it would still be a good idea to spray something over that as well.  I saw that upol now makes a Raptor brand 2k aerosol Berliner.  Looks like some tough $hit.  Pricey to say the least.  I thought it might be possible to spray the ospho, let it do it’s magic. And then neutralize is after and hit it with the raptor stuff.  But then again, I could just as easily spray the ospho, then hit it with rubberized undercoating throughout and call it a day. Long post, but this is just some of the million places a mind wanders when going over options.  Here is what I am looking at.  

 

[machattack]

Hi,

Anything you do will be better than what was done at the factory.

I personally use por-15. Just wire wheel it to remove some surface rust and debris then brush por-15 over it. That stuff is harder than the back of my head treats right over rust as well.

Have fun and keep smiling

 

[BrewSTL]

Hi,

Anything you do will be better than what was done at the factory.

I personally use por-15. Just wire wheel it to remove some surface rust and debris then brush por-15 over it. That stuff is harder than the back of my head   treats right over rust as well.

Have fun and keep smiling

thanks for the input!  I should have mentioned that I have actually worked with por15 previously on the floor boards or my car.  I actually loved the result.  When I did that I used an entire kit with the metal prep, degreaser, etc.  are you saying that you just knock off the surface rust and go straight away with the por15?  I was under the impression you are supposed to neutralize the rust before applying the black por15 paint.  But if I can get away with it being that simple it would be my go to solution for sure.

 

[machattack]

Hi,

Anything you do will be better than what was done at the factory.

I personally use por-15. Just wire wheel it to remove some surface rust and debris then brush por-15 over it. That stuff is harder than the back of my head   treats right over rust as well.

Have fun and keep smiling

thanks for the input!  I should have mentioned that I have actually worked with por15 previously on the floor boards or my car.  I actually loved the result.  When I did that I used an entire kit with the metal prep, degreaser, etc.  are you saying that you just knock off the surface rust and go straight away with the por15?  I was under the impression you are supposed to neutralize the rust before applying the black por15 paint.  But if I can get away with it being that simple it would be my go to solution for sure.

Chances are you dont have any grease on the fender, but do check. That would stop adhesion. 

Certainly you can paint right over rust. It says it on the front of the can. However Im a bit anal for doing more than needed. I think it just makes me feel better about the job. 

There is a product from Home depot that is blue liquid comes in a gallon jug. I believe its called concrete and metal prep. Its in the paint department. Spray or soak rusty metal parts and Bam.....it eats the rust away.

 

[turtle5353]

I would use the Por-15, its bad ass stuff. But if you decide to go the bedliner route, the raptor stuff is pretty good. I used it on the yellow mach 1 i did a couple years ago. But i used the sprayable kind not aresol. I would shy away from rubberized undercoating, to me its cheap junk that doesn't look good. The bedliner helps with some sound deadening from road noise and keeps rocks from denting up the fender from inside. I coated the whole underside of the car and trunk with it.

 

[SVO2SCJ]

That fender has beautiful aging patterns! What year is it? Tell a lot how Ford built cars and the order of assembly. I would take my restored cars off and try to UNFIX prior owners "efforts" in a flash if I could get that look. (hard to do when "restoring" a car as you have to AGE the materials)

Mark

 

[red351]

It's always good to have some kind of thick coating on the top underside for when a stone gets throwed up there. Pimples never look good no matter where they are.

 

[Bentworker]

I just did this to my fenders.

Started out with a heat gun and narrow thin putty knife to scrape off 95% of the undercoating.

Next came aircraft stripper to remove the paint and remainder of the undercoating.

I have a media blaster so I used it to hit the rusty spots.  Phosphoric acid works too (concrete etch) but it takes time and elbow grease with abrasive cloth or wire brush.

Lastly I used an old bread knife with some abrasive cloth and phosphoric acid to get between the fender skin and brace.  It was 99.98% bare steel by the time I was done

 

[Carolina_Mountain_Mustangs]

The factory for sure did a hit an miss on the little bit of undercoat they did spray inside the fenders. Like stated it was to help with the rock dents since there was no liner in there. 

Since the fenders were painted off the chassis they got some over spray inside but not a lot of body color.

While you have the fenders off get you a stainless steel scrubber pad and cut a piece and put in each of the cowl drains. there is a built in walkway for mice and critters to walk right to the drain and go inside the cowl and build nests and store acorns and such. Water can drain and SS will not rust. I also cut pieces of the 1/4" mesh wire and paint black and zip tie to the back side of the plastic cowl vents to keep little ones from going in that way. If you ever have the heater box off I put a piece between the box and cowl and that way no critters get in the car. 

Another job while the fenders are off it to wash your plastic splash guards with lacquer thinner and if they still do not look good I blast with walnut shells and spray with satin clear. They look like new.

If you want to add to the snowball the shock tower cover was slop gray, lol.

 

[BrewSTL]

Wow that’s a whole lot of great advice from everyone. I’m going to go the route of por15. And that’s only on the basis of having previous success and the fact I plan on doing the same in the trunk area and top coating with the aerosol raptor 2k bed liner. I pulled the other fender today and was taken aback at just how good of shape it is in. Funny someone mentioned acorns and nests. I pulled this car out of a barn going on 7 years ago and it was absolutely loaded with all the typical nut storage spots. Here is a picture of the driver side I pulled today.

 

[Hemikiller]

I used a combination of blasting, wire wheels and phosphoric acid to get rid of the surface rust and road gunk on the underside of my fenders. Final prep was POR-15's Metal Ready, which is now utter garbage. I now use Metal Blast from Rust Bullet, it removes any remaining flash rust and leaves a zinc phosphate finish which ******* rust and helps with adhesion. Final topcoat was POR-15 black, which again, I don't recommend anymore. My new chassis paint of choice is Rust Bullet. Be sure you use a thick spray on undercoating type material on the top of the RB in the factory applied areas, which as others have mentioned needs protection from stones. The thicker, the better.