How to Best Prepare the Rolled Fender Skin

[cary]

I'm looking for the best practice for preventing rust from coming thru the crimped skin lip on my 914.
Here's where I'm at.



I opened that area up with my air die grinder. The folded over material (backside) seems fairly solid. It cleaned up real nice with a wire wheel. The outer skin itself seems to be the issue.

[Dpmulvan]

I use ppg metal cleaner followed by metal conditioner which forms a phosphate coating.

[cary]

That's plan a.
The top portion is new. I might just open up the rest and treat it. Then weld it back up.

[rich]

Cary,

What your seeing is caused by moisture intrusion behind the seam sealer that is on the back side of the fender in that area. Over time it will crack and fail in one place or another allowing moisture to get trapped in there and eventually rust from the inside out. The best thing to do is remove the seam sealer, get in the tight space and neutralize the rust, epoxy coat it and re-seam seal it.

[cary]

Rick,

The seam sealer is gone. I've already opened up the rust section in the picture with the edge of my die grinder. I'm planning to treat the opened area with OSPHO. Then treat the backside with more OSPHO. But will that be enough?

I just hate to do all this work and have the rust come back .................

My master plan is to use brush on 3M seam sealer in most welded areas and seams. Then two coats of epoxy primer. Then spray on Fusor seam sealer.

[rich]

Sounds like your on track.

[cary]

I cut the outside edge to the bottom of the fender. Gave both side a good spray down with OSPHO.
All the flat metal looks pretty good. I didn't see much of a reaction after 3 hours or so.

On to seam sealing.

[962porsche]

can I ask as to why you did not just sandblast the rusted areas with a hand held spot blaster .
rust treatment products have there uses but when you can get to both side it's not at all the time you would want to use it .
if you needed to get down inside a boxed area it's one thing.
most people over use rust products like ospho .

you have what looks like a crap load of holes in the edge and because you cut the edge and hammered back that now you have a ever uneven (straight ) fender edge .
put a straight edge up to it and see how far off it is now .
what is your fix going to be for that ?
you treat the rust then you have to weld in the holes and then add metal back to the edge you hammered in . you will burn off any treatment you go on there and then from welding the fumes of the burning ospho is far from healthy for you .

if that job was in my shop I would have simply cut out the rusted area made a simple patch welded in the patch so the edge would be as it was when VW made the 914 .
you would not have any rust to ever deal with your fender edge would be straight so the door to fender gap would be good also .
the way it's getting done now you have many more hours your spending on one little area and you still have rust and a gap your going to have to deal with .

as for seam sealers use a two part seam sealer . this way it will not shrink crack and dry out later on down the road .
there should be no reason for a sprayable seam sealer that is a product for seams on things like floors were you have over lapping panel seams . lift up the trunk mat in your newer car and you will see where it's used .

[cary]

cutting a patch was Plan A. but on the 914 that fender edge isn't straight. so I couldn't figure out how to bend/cut the edge after I create the patch with the folded over double edge.

the backside was blasted with the spot blaster. but I was paranoid of what could be hiding under the folded edge. and yes I made a mess of the sheet metal. overworked it.

[962porsche]

you would make a oak buck to form the shape .
if you can't do it out of all one piece because you may not have all the tools to do so you would do it in two parts . the out side skin then the inner part and weld them together then weld the patch piece on the fender .
if you sand blasted the inner fender then using a product like the ospho would do nothing to good clean bare metal . it would be best to use a etch primer on the inner fenders . it will give the bare metal etch you need and also be better to stop any rust year later down the road .
I'm one that doesn't like to use any type of product that the auto makers them selfs don't use or is not made by the paint manufacture . I have seen to many times after market rust products fail many years later and make a bigger mess then if the person just use the right products from the start . last year I had to strip a hole car back down to bare metal after the owner though it would be a good idea to coat the hole car with one of the rust treatment products right after he had the hole car blasted down to bare metal 3 years before I had to redo the hole car for him .
he was not a happy camper after spending 4 years restoring his car to find out 3 years later the primer is coming off in sheets because of a metal product that the co that makes it said it's good to use it but the paint CO said you shouldn't use it under our products .

[cary]

lets just say this is my test/training mule. I have 4 more 914's to restore.
we bought this car for $1100 for my oldest son to drive thru high school in Montana. it got used pretty hard for 4 years. I'm rebuilding it to be my forever daily driver. living here in Portland i'm working real hard to protect it from moisture and rust. somewhere in its childhood it had a front clip repair. so we're not working on a virgin here. its more about function.

thank you for taking your time to help us DIY'rs do our best work. because of the rust on this car i'm going with a epoxy primer that has proven to be compatible with OSPHO.
Southern Polyuerthanes, Inc.
I spent lots of hours scouring over the hotrod and autobody boards to make my choice.
I feel good with the compatibility of OSPHO and SPI. Using them under Deltron 2000 is a roll of the dice. I know your feelings on mixing product lines.

I'll do some reading up on making and using a buck.

[cary]

So I watched the Fusor door skin install video. So I assume on new cars there's no welding at all on the hemmed edge. That would be nice.

When I get back out to the car. Next Week. I'll make plans to cut out the fender edge where the hem has been compromised by rust. Anything short of that will leave me vulnerable. It seems about every other 914 that is a daily driver starts to rust on the hemmed fender edge.

[cary]