How to deal with rust on inner fold/lip of rear fenders?

[95maxrider]

My car has some moderate rust on the inner folds/lip on the rear quarter panels, likely due to the fenders being rolled 15 years ago. My very first welding project involved cutting out and replacing the completely rotten metal on both rear fenders. No replacement panels are available in the aftermarket, so I had to find cars in the junkyard with metal that was in good enough shape. Considering my car is 25+ years old and I live in the mid-Atlantic, this was a bit of a challenge. Here's a couple pics of what I've done so far. Please keep in mind that I'm a complete novice with both body work and welding.

Outside

Inside

Helpful advice welcome

So here's what I need to deal with next:

I'm guessing that when the lip was rolled it pulled apart the inner and outer skins, allowing moisture to get in between them.

I recently purchased a big tank for media blasting (link) and an air compressor. I also plan on getting into using Ospho.

Keeping in mind my skill set, availability of replacement metal, and available tools, how should I approach this? Do I cut out the rest of the inner skin, blast it, spray it with SPI epoxy, and weld it back in place?

 

[dhutton01]

That is not deep cancerous rust. Lightly blast it, epoxy prime it , and move on…

Mandatory backyard hack disclaimer.

Don

 

[95maxrider]

That is not deep cancerous rust. Lightly blast it, epoxy prime it , and move on…

Mandatory backyard hack disclaimer.

Don

Even that hole in the center? That area looks pretty deep to me.

I'm concerned about what's going on in between the two sheets of metal; I have a feeling the lip is going to rot from the inside out.

An idea that had crossed my mind was to cut the top half of the part of the lip that you can see (which is the outer panel) off completely, as that's the part that's showing the worst of the rust. This way I would have access to the top half of the inner skin to better blast/coat/seal it, and since the lower half of the outer skin would still be there, I don't think the structural nature would be compromised. I want to get ahead of this rather than play catch up in 5 years.

 

[dhutton01]

It sounds like you are determined to pursue perfection and do some cutting so have at it.

Don

 

[RenewAP]

No matter what you end up doing, spray some cavity wax onto the repaired area after all painting is done. Spray can with a wand is around $25. It may drip some for a few hours, and then again on hot days, but it will seal the areas that you can't get direct paint or primer on otherwise. Drips clean up easy with wax and grease remover.

 

[95maxrider]

No matter what you end up doing, spray some cavity wax onto the repaired area after all painting is done. Spray can with a wand is around $25. It may drip some for a few hours, and then again on hot days, but it will seal the areas that you can't get direct paint or primer on otherwise. Drips clean up easy with wax and grease remover.

I plan on spraying cavity wax inside the quarter panel when I'm all done, but I didn't think the wheel well was really the place where CW would be the best product. The CRC HD Corrosion Inhibitor has been shown to be very effective for exposed areas like this, or something like Raptor lining may also be used.

It sounds like you are determined to pursue perfection and do some cutting so have at it.

Don

Yeah, I have a tendency to do that. I want this car to last another 25 years, so I want to tackle this rust problem to the best of my abilities now before it gets out of hand and I have to do more major surgery later. But as a newbie I'm not sure what the proper path is.

 

[RenewAP]

Yes, just between the quarter panel and tub. Cavity wax will not hold up to the exposed underside of the tub. The rust is from the inside, so that's where the sealing needs to be done. If you Spray a bedliner on the underside, do it before the cavity wax.

 

[Chris_Hamilton]

Being you said you want the car to last...in your pic of the inner lip, that one area there is more than surface rust. Just putting something on it probably won't stop it. That is a common area for those cars to rust. Above the lip I would poke around with a screwdriver and see if you can push through. Eventually that area will come through as the foam sealant used between the 1/4 and wheelhouse traps moisture. No real easy fix other than replacing what you can.

 

[dhutton01]

If you do cut it please post pics of what you find.

Don

 

[chevman]

 

[dhutton01]

That almost looks like a busted out spot weld to me but I have no idea what was there before the lips were cut and rolled. At least I assume they were cut before being rolled.

Don

 

[MJM]

View attachment 24368

For this repair I would gently pull the folded over lip away from the panel just far enough to get a piece of copper backer between the folded lip and quarter panel.

Once the folded metal was pulled back, I clean up the rust to clean metal. Once that was done, I'd slip a piece of copper between the folded over lip and quarter panel and weld it up.

 

[MJM]

If you do cut it please post pics of what you find.

Don

I think he would find very light surface rust that could be handled by applying epoxy primer to stop the spread. A syringe filled with epoxy would surely get the epoxy between fender lip and quarter panel.

 

[95maxrider]

Being you said you want the car to last...in your pic of the inner lip, that one area there is more than surface rust. Just putting something on it probably won't stop it. That is a common area for those cars to rust. Above the lip I would poke around with a screwdriver and see if you can push through. Eventually that area will come through as the foam sealant used between the 1/4 and wheelhouse traps moisture. No real easy fix other than replacing what you can.

From what I saw when I cut apart my car and those at the junkyard, there is no foam between the panels:

That almost looks like a busted out spot weld to me but I have no idea what was there before the lips were cut and rolled. At least I assume they were cut before being rolled.

Don

The lips were not cut before they were rolled, what would that have effected?

For this repair I would gently pull the folded over lip away from the panel just far enough to get a piece of copper backer between the folded lip and quarter panel.

Once the folded metal was pulled back, I clean up the rust to clean metal. Once that was done, I'd slip a piece of copper between the folded over lip and quarter panel and weld it up.

I'm having trouble visualizing/understanding this. What's the purpose of the copper here?

Let's say I get the two pried apart and am able to clean them up and paint them, when pinching them back together, what should be used to lock out moisture, seam sealer?

 

[Chris_Hamilton]

From what I saw when I cut apart my car and those at the junkyard, there is no foam between the panels:

Yeah forgot this was a 93(?). They didn't start using foam till the 2000's.
That spot is rotting from. looking at the picture. The inner panel in that spot looks rotted too. It is where the spot weld was. The backside of the inner panel is where the rust is. Probably looks much worse on that side. Without taking the 1/4 off (not saying to do that) anything you do is just going to be a stop gap.
If you can peel the lip back, you could then try and patch that spot on the inner panel the turn it back over and weld it back to the inner panel.
About all you can do without resorting to extreme measures.
If you drill a hole or two in the inner wheelhouse, you could spray some cavity wax in the area between the 1/4 and inner panel around the lip. It will hold up as well as anything else in this situation. Plug the holes you drilled with seam sealer when you finish.

 

[MJM]

Putting a piece of copper between the folded lip and quarter panel will not allow the weld to weld itself to the quarter panel. You will remove the copper after your done welding.

I'm right in the middle of something but will post pictures of what I'm talking about in an hour or so.

 

[95maxrider]

Yeah forgot this was a 93(?). They didn't start using foam till the 2000's.
That spot is rotting from. looking at the picture. The inner panel in that spot looks rotted too. It is where the spot weld was. The backside of the inner panel is where the rust is. Probably looks much worse on that side. Without taking the 1/4 off (not saying to do that) anything you do is just going to be a stop gap.
If you can peel the lip back, you could then try and patch that spot on the inner panel the turn it back over and weld it back to the inner panel.
About all you can do without resorting to extreme measures.
If you drill a hole or two in the inner wheelhouse, you could spray some cavity wax in the area between the 1/4 and inner panel around the lip. It will hold up as well as anything else in this situation. Plug the holes you drilled with seam sealer when you finish.

Yeah, it's a '96. I can access the inside of the lip area through the trunk, so luckily I don't need to drill holes anywhere to spray cavity wax. If the two pieces are spot welded together (which they must be, right?) I would need to find and drill out the spot welds to be able to pry the two apart. Which would definitely suck.

How bad would it be to simply cut and permanently remove 50-75% of the lip you can see (which is actually the outer skin), leaving just enough at the bottom to maintain the fold over area? This would eliminate most of the area where moisture can get between the panels, and would give me great access to the remaining inner skin for blasting the painting.