Rust at interior seam in trunk - 91 MB

[JHZR2]

I got a great deal on my 91 MB 300D knowing it had a surface rust spot on the trunk, and some clearcoat failure.

It rained a lot recently, got some water in the cabin, and looked around the car quite a bit. Also had to swap an amplifier (the car really has great sound now that both front channels are playing - very impressed).

But when I pulled the trunk liner to check for moisture and change the amp, I saw this:

I think water gets down under the taillight gasket, and sat along that pinch weld seam, seeping in over time and causing it to crumble. The second and third photos show a pile of rusty bits that are actually the crumbling of the punch weld in those photos. I don’t believe the spot they’re sitting is actually rusty.

Obviously I need to pull the taillight and replace the seal. Who knows what I’ll see there. The question really becomes:

How do I stabilize surface rusty metal assuming it doesn’t have perforation?

How do I deal with that pinch weld that is decomposing, to at minumum stabilize the metal and prevent any additional rust?

I’ve had decent luck in certain applications with ospho and POR patch. I don’t weld thin (or any) metal, though I’d be willing to learn. I’m not sure this is the location to learn though…

The car runs absolutely beautiful, has a perfect blue interior, AC works well, etc. It’s a driver, not a collector car though, so I’ll spend money and time, learning opportunities too.

So… recommendations to stabilize and fix?

Thanks!

 

[xgmad]

1. Sand down areas affected with rust

2. clean rust with wire brush/wheel , or chemical (rinse off)

3. stick weld and then grind, what matters more is that integrity is held up rather than looks.

 

[xgmad]

naval jelly might help you with this too.

 

[supton]

How good do you want it, and how much work are you willing to put in?

Me, I would probably wire wheel a bit and splash Rustoleum Rusty Metal primer over it, mostly because that is what I’ve been doing lately.

 

[spasm3]

I would remove all I could wire brush/scaler down to bright metal. Clean it down with denatured alcohol. Then when dry, I'd mig weld to add metal, does not look structural, so welding it a bit cold should work, you just want to add metal. Grind that smooth and coat with a rust converting primer or por 15. Then paint.

 

[DuckRyder]

Need to see what the other side looks like.

Also need to vacuums up the lose flakes and any other detritus and see what we really have.

Provided no openings Id go with clean and descale, prime and paint or POR15.

 

[SC Maintenance]

I have had good luck so far with 1) clean off rust with wire wheel or sanding or whatever, 2) convert rust with jenolite rust converter, and 3) topcoat with rust bullet topcoat.

To be fair we don't have salt here and its only been a couple years on one spot I did in my drip channels (fix for bad nissan paint). I am about to do another spot that is just starting to bubble. I found these 3 from much internet research so who knows.

The only real cure once it starts is to cut it out, but if you neutralize it and seal it, and keep whatever is causing it off - you might get many more years out of it.

 

[joegreen]

You can neutralize the rust. Maybe clean everything up with a wire wheel. Coat it and then fiberglass over any thin spots.

 

[MrGraybeard]

You can neutralize the rust. Maybe clean everything up with a wire wheel. Coat it and then fiberglass over any thin spots.

That's what I'd do. The car may be distinctive, but it isn't all that valuable and the rust spot isn't in a structurally important place. The important thing is to seal out the water. I'd get some POR-15 and, if necessary, some fiberglass cloth for patching thin spots/holes. The cloth with half a dozen coats of POR develops a very firm surface.

 

[mattd]

See how far that rust has penetrated and go from there. You need clear margins, just like cancer.