Rust spot treatment

[redstack]

I hope this isn't considered bad forum form, I had posted this in paint and autobody, but received no feedback.
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I'm looking at an 84 ROW Carrera, that has only one rust spot on it. I'm sorry I don't have a picture of it, but I'll try to describe it.
The drivers side fender, on the inside lip, where the trunk lid gap is. On that vertical surface facing the trunk lid, there is a 2" section of rust. My thought is that it was either a replacement fender that was poorly prepped, or some how the trunk lid was misaligned so that it was hitting there for a while.

Until the PPI is done I have no real idea about how it happened, neither does the current owner. Even the mechanic doing the PPI suggests that it's beyond his field of expertise. But I think he will know if it took a hit on that side that would cause a fender to be replaced.

My real question is how to repair it. My thought would be to mask it off above then remove the rust with one of those abrasive pens, por 15, topped with touch up paint. A light sand and buff.

My reasoning being that due to it's position, it wouldn't be visible but would definitely want to stop it from spreading.

Oh and I'm 3000 miles away from the car even though it's right next door to my home. So this is all based on memory.

Any thoughts oh wise and wonderful mechanics who worship Weissach?

[Rich76_911s]

I'm guessing the rust is half way up the fender? If so this is a fairly common spot. The lines for the gas expansion tank and or the windshield washer tank hold dirt and grime up there that gets wet and stays that way then. Which leads to rust. I'm an expert at finding rust but not repairing it. If it were me though I would probably take the fender off to do the repair properly. You might also find some rust on the inner fender wall when the bumper shocks moint to the car.

[porwolf]

Originally Posted by Rich76_911s

I'm guessing the rust is half way up the fender? If so this is a fairly common spot. The lines for the gas expansion tank and or the windshield washer tank hold dirt and grime up there that gets wet and stays that way then. Which leads to rust. I'm an expert at finding rust but not repairing it. If it were me though I would probably take the fender off to do the repair properly. You might also find some rust on the inner fender wall when the bumper shocks moint to the car.

Yup. Surface rust on Porsche, especially if it is not smooth but more rough, could be the tip of a rust-berg underneath. Especially if the rust spot is on the surface of an interior hollow space. Ask me how I know.

[DGriz]

I suggest removing all rust scale with a wire wheel, wiping well with solvent, and painting with Eastwood's rust encapsulating paint. It does not need a tie coat like POR 15. Then fill, sand, and paint to disguise the repair.

If done correctly, the rust will not come back. Good luck. Dickson

[redstack]

Right, PPI tomorrow, we'll see if the Mechanic has any thoughts.

I will look up under the lip when I get the chance, to see if it's just surface rust or continues on the inside.

[javadog]

It's just about guaranteed that the inner fender joint is rusted. Porsche hung the fenders on the tub before much rust proofing was done and the result isn't pretty.

You will need to pull the fender off to do any serious remediation.

JR

[redstack]

Well the PPI shows that it hasn't gone beyond the lip area. So I'm hoping that once I get my hands on the car I can follow my plan.

Thanks guys, I will look under the lip when I get it so that I can make a final plan to stop the rust.

[Bob Kontak]

Originally Posted by javadog

It's just about guaranteed that the inner fender joint is rusted. Porsche hung the fenders on the tub before much rust proofing was done and the result isn't pretty.

You will need to pull the fender off to do any serious remediation.

JR

Bingo!

Mine was pitted where the inner fenders was welded to the tub - only on passenger side.

[bpu699]

Originally Posted by DGriz

I suggest removing all rust scale with a wire wheel, wiping well with solvent, and painting with Eastwood's rust encapsulating paint. It does not need a tie coat like POR 15. Then fill, sand, and paint to disguise the repair.

If done correctly, the rust will not come back. Good luck. Dickson

I had a 76 911s. Had a bit of rust around the head light. I sanded it, used a rust converter, primer, and paint.

2 weeks later, rust was bubbling up again.

Years later. Same issue, different car. Sandblasted the spot, metal- preped with phspho equivilant, epoxy primed, painted. Within 6 months, rust was coming back through.

Perhaps you guys have better luck, but what I have learned is that the only real treatment for rust, is cutting it out big time...

Bo