R230 rear arch rust repair - grind back the lip?

[conor1n]

Hello guys,

Just a quick question. I have started work on repairing the rust on my rear arches and hit a bit of a conundrum. Wondering if you guys can help?

You will see in the drawing below, a rough outline of the rear arch and internal lip. I need to remove all the rubber sealant in the lip along with the rust. The problem is that it is all quite difficult to get at with grinder/sandpaper and possibly fill up with dirt again after repair. This has led me to consider grinding back the lip a bit, as highlighted with bright green line.

Is this advised against? I am trying to figure out any possibly downsides to this.

The plan is to bring back to metal with sandpaper + wire wheel, then use Bilt Hamber rust remover + converter after, followed by some epoxy primer/sealer to seal and fill the lip/protect edge.

There is no going back after I grind the lip down a bit.. good or bad?

 

[R129mine]

If you grind it down it will make did a very sharp body panel. I would not grind it down.

sand down as much as you can. Remove as much of the rubber sealant and perhaps inspect with a small camera

I would then apply dinitrol rc900 (rust converter) or Bilt Hamber deox gel to convert remainder of the rust.
If using dinitrol use something like underbody wax 4941 or bolt Hamber mastic epoxy to protect.
I have never understood the water and dirt trap that is created by this lip.

perhaps considering using something to seal off th lip so no new dirt and water can get in there.
Good luck

 

[ChipChop]

Some gentle heat will soften up that sealent (looks like brush on seam sealer in your photo) and then you should be able to just peel it off.

A paint stripper gun on low heat would do the job. Obviously be mindful of the exterior paintwork and if there are any fuel fillers in the area.

Saying all that your arch inner lip does look pretty well corroded and pitted so the only real way to stop that is to cut it out and replace with new metal.

Drastic and costly, unless you can weld, but it is an SL so long term will be worth it.

 

[KillerHERTZ]

No point in sandpapering it will never get rid of old rust. Need an angle grinder with a wire attachment on that.

 

[219]

Hello guys,

Just a quick question. I have started work on repairing the rust on my rear arches and hit a bit of a conundrum. Wondering if you guys can help?

You will see in the drawing below, a rough outline of the rear arch and internal lip. I need to remove all the rubber sealant in the lip along with the rust. The problem is that it is all quite difficult to get at with grinder/sandpaper and possibly fill up with dirt again after repair. This has led me to consider grinding back the lip a bit, as highlighted with bright green line.

Is this advised against? I am trying to figure out any possibly downsides to this.

The plan is to bring back to metal with sandpaper + wire wheel, then use Bilt Hamber rust remover + converter after, followed by some epoxy primer/sealer to seal and fill the lip/protect edge.

There is no going back after I grind the lip down a bit.. good or bad?


View attachment 98541
View attachment 98542

Once you’ve ground back and got rid of all the rust / treated and repainted all the surfaces , why not mix up some kind of filler , perhaps even fibreglass resin to fill that channel so that dirt and water can’t get back in to cause problems?

 

[exvolvoman]

I've just done the rear n/s arch on mine and managed to remove the rust from the inner lip using a wire brush like this in my cordless drill and using a mirror & torch to check progress.
Then applied liberal coat of Kurust, followed by underseal

 

[R129mine]

I have used these on my angle grinder. Works really well only on flattish surfaces

 

[horatio]

My tactic has been: get back to metal as much as possible - treat with metal prep, a few coats of POR15 then touch up paint to finish. It has lasted years on the W211 I did and it hardly notices.

 

[amazighman]

The way I have done it in the past , with great success.

Remove as much rust with a wire wheel

Apply deox gel and cover with cling film

Reapply the gel and cover maybe 1 week or more as needed untill clean metal is showing and no signs of remaining rust.

Apply Epoxy Mastic to the area and leave to dry properly.

Paint with your choice of top coat.

Use bilt hamber Deox gel which is a rust remover , rust converters dont really work , they convert top layer but the corrosion remains underneath eating away the steel.

 

[mercman111]

there is only one way to remove rust as it comes from the inside to the outside, thats to remove it

 

[Petrol Pete]

Rust never sleeps.....

 

[amazighman]

I did a W210 and W208 rear arches before, the rust wasn't inside out , it started from the lip inner edge .
Due to poor thin factory paint which lifts from the edges and allows moisture in ,

On mercs of that era None can stop them rotting.... Unless full strip , acid dip and proper paint .

Usually the rust You see on these is the tip of iceberg.

 

[mercman111]

you just critisized yourself amazinghman,you said the rust wasnt inside out,then you said it was the inner lip of the wheelarch,what i said was right

 

[amazighman]

you just critisized yourself amazinghman,you said the rust wasnt inside out,then you said it was the inner lip of the wheelarch,what i said was right

I meant the arch lip as it folds towards the well.
Inside out rot means panel is rotting from behind.
End of the day I did few cars this way and repair lasted , If You are one of them that think they know it most , then just be happy , you are right and everyone else is wrong.

 

[mercman111]

im not one of those

 

[amazighman]

Apologies....

 

[mercman111]

apology accepted

 

[conor1n]

Hey guys,

Good feedback thanks. As pointed out where the rust begins.. agreed, that's where mine started. I actually ended up cutting off that inner upper lip part. About 15mm that runs perpendicular to the road. The inner bit running parallel to the road is still there. It's coming together nicely and I have eliminated all the rust.

There is currently one belt and braces application of Deox Gel on there now and then I move to the next stage.

Here is a cross post, update from elsewhere, if you guys are interested:

Busy week everybody.....

And for my next trick: A post that is certainly not for the squeamish / faint of heart when it comes to chopping lumps off your prized automobile..

I did plenty more inspection and just couldn't figure out how I was going to confidently get at / remove "all" the rust without removing the inner lip of the arch. It just had to go :/

I cut off most of the vertical piece of that inner lip, as shown in various photos below. I will be first to admit the job I ended up doing certainly won't win any prizes. And some might argue it should never be done, for risk of splitting the arches.

With that said, after getting over the fact that I butchered my car, I took some solace in finding rust inside where the inner arch/wheel well and quarter panel meet. This would have been impossible to get to, but now it's gone.

-- Slide aside--
Once the fix is done I am going to get some U channel (Thanks @television for the tip!) and run it along where I chopped off. I am not sure if I would fill the U channel with seam sealer or wax oyl..and if I would covert the U channel with Seam sealer after. I need to get advice on how to approach that and not do a shotgun approach while missing the target....
-----------------

Now that I have put away grinder, before I could do any more damage preparation. I moved onto treatment. Cleaned up with BH Surfex and ensured it was dry with heat gun.

Next up was Bilt Hamber Deox Gel (Rust Remover) all over the exposed metal and covered with Cling Film and covered with carrier bag to protect from the rain.

Tomorrow I will be washing all the Deox Gel off with Surfex was and Methylated spirits and inspecting. I may apply more Deox gel or get the Dremel out with grinder to clean up some missed spots before more gel. This is a very tricky job and there are many intricate places to get to, primarily down around the rear bumper join area and the side skirt join area. I think I will remove the skirts tomorrow as they are kind of in the way and I want to ensure I have no small bits of rust hiding.

Progressing from the rust remover to following stage is time sensitive as I don't want the metal to be exposed for any length, as even the humidity in the air can start the rust process again.. With that in mind, I have my BH Hydrate 80 rust converter to apply to the metal to pick up any missed rust and then I will apply some 2K epoxy primer I picked up. Beware that anything 2K is extremely hazardous to your body. I need to get some proper respiratory PPE before applying that.

I think that's it for the moment.

This thread has some high level photos and I will share more in depth ones after. I have tried to take some decent photos/angles of the arch lip that I chopped off so that you can see how the pieces have rusted etc.

Below you have the arch: Before, the removed piece and after removal.

 

[conor1n]

 

[conor1n]