# Treating rust on my SL 500 arches..



## conor

Hi guys,

So anybody familiar with the R230 SL 500, will know the wheel arches have a flawed design that encourages rust over time.

I need to treat mine. They are at the stage where there is significant surface rust but nothing that requires cutting/welding imho.

My plan for treatment is:


Physical removal of rust - Grinder + wire wheel.
Chemical rust remover (Bilt Hamber Deox Gel)
Chemical rust converter for remaining rust (Bilt Hamber Hydrate 80)
Seal with epoxy primer
Fill the inner arch lip with something like seam sealer or silicone
Paint + Clear
Waxoyl or similar

First post is bumper removal - if any body needs further instruction/help on how to remove the bumper DM me. It's complicated and time consuming. It took me 3.5 Hours to get the bumper and both arch liners out.


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## conor

Following the removal of the bumper - I cleaned out the inner lip of the arch so there was no grime/grease. I used very soapy water and a piece of cloth to do this.

I discovered that there is a rubber treatment on the inside that is to prevent rust. The problem is the edge wasn't protected properly and when the paint got damaged, I the moisture/rust crept in under the treatment. Now it all has to go.

I discovered that it will be difficult to get a machine into the lip so I will need to hand sand.

*I will also need your help with whether or not it is a good idea to grind back a bit of the lip to aid access and also prevent further build up? You can see what I mean in the first diagram.
*

Please don't be alarmed by the rust photos.. I don't think the rust is as bad as it appears.. it is very much just surface rust still and I will be able to remove it all.


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## grunty-motor

that looks nasty - gonna be hard to totally eradicate. The rubber sealant is just panel seal i think where the inner/outer arch come together.

If its only surface rust, you have a fighting chance, and i wouldnt cut the lip in that case.


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## conor

grunty-motor said:


> that looks nasty - gonna be hard to totally eradicate. The rubber sealant is just panel seal i think where the inner/outer arch come together.
> 
> If its only surface rust, you have a fighting chance, and i wouldnt cut the lip in that case.


Hi,

What do you mean, inner/outer? Do you mean double skin? Because I am lead to believe there is no double skinning from the MB experts on another forum.

The rust looks bad alright but I am. Confident I can treat it.

Why would you not grind back the arch?


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## AndyN01

Wow! What a huge amount of work to get at something most folks wouldn't be bothered about or would just give to someone else - fair play to you :thumb:

I'd clean/sand/grind off just enough to get to clean, bare metal. I wouldn't be grinding the original lip away unless absolutely necessary. Whatever is taken off will need to be "replaced" in some form or other so you may be making way more work than is needed.

Treatment is spot on with BH products.

Not too sure about the use of silicone to fill the inner lip. I totally understand the reasoning - if there's no gap to get full of crud then the chances of rust coming back is much reduced. However, if rust starts again behind the silicone or creeps under it then it'll be an absolute pain to get out to attack. That's what's happened with the "rubber treatment" from the factory.

How big is the lip? Might you be able to fill it with a Waxoyl based underseal that will move about as the metal flexes with car movement or temperature?

Just a thought to add to the mix.

Beautiful colour by the way and I love the garden chair......

All the very best with it.

Andy.


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## Starbuck88

Looking good. Just remove as much surface rust as is possible using your products, then use the hydrate 80 and then cover over the inside of the wing/over the hydrate 80 with Bilt Hamber UB. That is designed to be under the car and in places where protective coating is needed.

Then the front/visible part of the arch lip, coat with hydrate 80 once you've done your rust removal then finish over it when a compatible primer and then your coloured top coats.


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## grunty-motor

conor said:


> Hi,
> 
> What do you mean, inner/outer? Do you mean double skin? Because I am lead to believe there is no double skinning from the MB experts on another forum.
> 
> The rust looks bad alright but I am. Confident I can treat it.
> 
> Why would you not grind back the arch?


No, not double skin - outer arch is the outer painted blue part & the inner is where the wheel tub is - the sealant will be where the join of the two bits of metal is. But i will admit I dont know that car (some cars have a inner/outer arches join at the lip and these are rust disasters!)

This is an E-type, but gives the general construction method. http://www.monocoque-metalworks.com/main/2013/11/ge-rear-wheel-arch/

yours doesnt look like it needs cut back, so that is good as all the sealant looks sound from what i can see

I would not CUT the lip off - by all means grind/wire brush as much rust off, but it wont look right without a lip

As mentioned above, the BH products will do a good job of slowing further spreading and short of completely cutting out, is going to be the best economic route. Even then you are going to have to filler/paint.

Not trying to put you off.........even though it might sound like it:thumb:


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## 11alan111

rust starts on the inside,there is no cure for rust,except cut it off and replace with good metal,all the rust treatments only slow the process down


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## conor

AndyN01 said:


> Wow! What a huge amount of work to get at something most folks wouldn't be bothered about or would just give to someone else - fair play to you :thumb:
> 
> I'd clean/sand/grind off just enough to get to clean, bare metal. I wouldn't be grinding the original lip away unless absolutely necessary. Whatever is taken off will need to be "replaced" in some form or other so you may be making way more work than is needed.
> 
> Treatment is spot on with BH products.
> 
> Not too sure about the use of silicone to fill the inner lip. I totally understand the reasoning - if there's no gap to get full of crud then the chances of rust coming back is much reduced. However, if rust starts again behind the silicone or creeps under it then it'll be an absolute pain to get out to attack. That's what's happened with the "rubber treatment" from the factory.
> 
> How big is the lip? Might you be able to fill it with a Waxoyl based underseal that will move about as the metal flexes with car movement or temperature?
> 
> Just a thought to add to the mix.
> 
> Beautiful colour by the way and I love the garden chair......
> 
> All the very best with it.
> 
> Andy.


Hi Andy,

Thanks for your message.

My feeling is that for a body shop to treat this rust properly would be super expensive, if possible even, given the labour involved.

I agree that silicon might not be best, I was thinking I could fill/build up with seam sealer.

If you look at my diagram above you will see the part of the lip I propose to remove. It's only the inner most part and I don't see what it is needed for.

My E Class doesn't have this kind of lip on it at all. As well as the other treatments, I am thinking of using some kind of rubber "U Channel" to place over the lip, in conjunction with something like Waxoyl.



Starbuck88 said:


> Looking good. Just remove as much surface rust as is possible using your products, then use the hydrate 80 and then cover over the inside of the wing/over the hydrate 80 with Bilt Hamber UB. That is designed to be under the car and in places where protective coating is needed.
> 
> Then the front/visible part of the arch lip, coat with hydrate 80 once you've done your rust removal then finish over it when a compatible primer and then your coloured top coats.


Ok, sounds like a couple nice additions to my plan. Is the Hydrate 80 sandable by the way?



grunty-motor said:


> No, not double skin - outer arch is the outer painted blue part & the inner is where the wheel tub is - the sealant will be where the join of the two bits of metal is. But i will admit I dont know that car (some cars have a inner/outer arches join at the lip and these are rust disasters!)
> 
> This is an E-type, but gives the general construction method. http://www.monocoque-metalworks.com/main/2013/11/ge-rear-wheel-arch/
> 
> yours doesnt look like it needs cut back, so that is good as all the sealant looks sound from what i can see
> 
> I would not CUT the lip off - by all means grind/wire brush as much rust off, but it wont look right without a lip
> 
> As mentioned above, the BH products will do a good job of slowing further spreading and short of completely cutting out, is going to be the best economic route. Even then you are going to have to filler/paint.
> 
> Not trying to put you off.........even though it might sound like it:thumb:


When you say it wouldn't look right without the lip, what do you mean? From an aesthetics perspective when looking at the car? Because the lip part I am talking about won't be visible from outside.. and I'm not talking about removing all the lip, just about 70% of the vertical piece so I can get better access.

The horizontal piece coming from the outside will remain in tact. You would only notice what I plan on doing if you had your head inside the arch or felt it with your hand (and had another car to compare to).



11alan111 said:


> rust starts on the inside,there is no cure for rust,except cut it off and replace with good metal,all the rust treatments only slow the process down


I'm not sure this is true. Surface rust can be removed completely.

It seems to be controversial but I have come across cases of successful jobs, where rust didn't return, but also ones where bubbling re-occurred after 6 months.

It would appear that it is all down to the extend of the process and/or treatment.


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## grunty-motor

conor said:


> When you say it wouldn't look right without the lip, what do you mean? From an aesthetics perspective when looking at the car? Because the lip part I am talking about won't be visible from outside.. and I'm not talking about removing all the lip, just about 70% of the vertical piece so I can get better access.
> 
> The horizontal piece coming from the outside will remain in tact. You would only notice what I plan on doing if you had your head inside the arch or felt it with your hand (and had another car to compare to).


Gotcha! dont see too much of an issue with that


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## Starbuck88

conor said:


> Ok, sounds like a couple nice additions to my plan. Is the Hydrate 80 sandable by the way?


Yes. I would however make sure that a full layer of it still exists over the rust, don't sand back down enough that you see bare metal again.

You can use their Electrox primer over it.


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## Barbel330

11alan111 said:


> rust starts on the inside,there is no cure for rust,except cut it off and replace with good metal,all the rust treatments only slow the process down


This is the truth.


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## conor

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.


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## conor




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## conor




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## conor




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## grunty-motor

keep em coming :thumb:


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## Nick-ST

Wow kudos to you sir and you definitely have bigger balls than me! 

Good luck and keep us updated :thumb:


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## James_R

Good work conor

Looking forward to seeing how this progresses.
Nice work


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## AndyN01

Hi Conor,

Fair play to you mate. I don't think I'd have had the erm.... guts, that's the word, sort of  to do what you've done.

Anyway, just another thought....

Maybe some BH Electrox zinc coating (https://www.bilthamber.com/corrosion-protection-and-rust-treatments/electrox) might be worth a look after the Hydrate 80 and before the epoxy primer. I've never used 2K epoxy primer so I may be talking out of my backside but there you go :lol:.

I'll be watching with interest.

Good Luck.

Andy.


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## SamD

Great read, keep us updated! It seems like you have some big man sacks to take it on.


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## conor

Hi everybody,

Thanks for the positive encouragement and yes it seems like a ballsy move. I certainly had to get myself together after cutting the chunks of metal off, but I feel good about it now, with all the clean metal in sight.

Cleared off the Deox Gel today and looking good. A few spots I will ream out with the Dremel and also some black spots I need to understand. But I will do another lash of Deox gel and then get into a bit of filing/priming, which will be the next test.

By the way.. what do people think of these products select? We have:


CarPlan fine surface filler (spec filler) - Note this is just to fill specs not overall.
Stevens Body Filler (2 Pak)
Tetrosyl brushable seam sealer
Spray Max 2K Epoxy-Primer Filler


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## conor

AndyN01 said:


> Hi Conor,
> 
> Fair play to you mate. I don't think I'd have had the erm.... guts, that's the word, sort of  to do what you've done.
> 
> Anyway, just another thought....
> 
> Maybe some BH Electrox zinc coating (https://www.bilthamber.com/corrosion-protection-and-rust-treatments/electrox) might be worth a look after the Hydrate 80 and before the epoxy primer. I've never used 2K epoxy primer so I may be talking out of my backside but there you go :lol:.
> 
> I'll be watching with interest.
> 
> Good Luck.
> 
> Andy.


Hi Andy,

Thanks for this.

I had seen all that product but figured I probably don't need it considering what I already have in the plan. It looks like that product is geared towards more extreme applications?


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## Starbuck88

Products look good, are you using hydrate 80 once you've done the Deox gel? Then primering over the Hydrate 80?


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## uruk hai

What a great thread, I'll be following this.


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## conor

Starbuck88 said:


> Products look good, are you using hydrate 80 once you've done the Deox gel? Then primering over the Hydrate 80?


That was the original plan but I think once the Hydrate 80 is dry I will go straight to filler and then prime.

Honestly I don't know though.. I'm a bit stuck. because I will need to key the steel with 80 grit to get the filler to bite and that would surely just negate the effect of any added Hydrate 80.

I honestly don't know yet.

With that in mind, might be better to Hydrate 80 -> Prime -> Filler -> Prime again?

- Unsure -


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## Starbuck88

conor said:


> That was the original plan but I think once the Hydrate 80 is dry I will go straight to filler and then prime.
> 
> Honestly I don't know though.. I'm a bit stuck. because I will need to key the steel with 80 grit to get the filler to bite and that would surely just negate the effect of any added Hydrate 80.
> 
> I honestly don't know yet.
> 
> With that in mind, might be better to Hydrate 80 -> Prime -> Filler -> Prime again?
> 
> - Unsure -


I intend to just fill over the hydrate 80, then prime, then paint. A very very thin coat of filler to make it all smooth won't need 80 grit. Thats very harsh.


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## conor

Starbuck88 said:


> I intend to just fill over the hydrate 80, then prime, then paint. A very very thin coat of filler to make it all smooth won't need 80 grit. Thats very harsh.


Ok thanks for clarifying I can fill over Hydrate 80.

I guess I ultimately don't need 80 grit for bite, because I am effectively only using the filler to fill in the pitting from grinder/wire wheel/rust, so it's very superficial.


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## conor

Ok guys,

So an update from me. On Sunday and today I took off the rust remover, which did a great job of cleaning up. Got plenty of clean metal now.

I then spent a nice amount of time, slowly inspecting and cleaning back the areas/corners/angles where the arch meets the front skit area and the rear bumper area. Kind of complex areas but I was sure to give them attention as they could easily be fobbed off.. and would be a total shame if they bubbled in 6, 12 months time after all this work. Clean metal there now too.

There are some bits of the original sealant there in places, but most importantly it is clean to metal around the edges of both arch time to ensure no rust. I am wondering now if I need to remove all of it, or if the final bits will be safe there as they seem pretty stuck on.

For cleaning the intricate areas I used my Dremel with 90 degree adaptor which worked great. Jury is out on the bits I used, especially the wire wheels / cups. They weren't OEM Dremel though only cheapo bits. I suspect Dremel bits would be ace. In fact any of the bits I have used are good. I am very dubious about using cheap bits because of the fear of a bit exploding at 20k RPM. I'll probably be only going Dremel from now, but they are expensive and somewhat consumable for this kind of work. -- I guess a die grinder tool is what I should really be using. Next time 

You will see in the pics, that I needed to use the cutting disc on Dremel to nob off a bit of this black plate that is used to mount the side skirt. The plate was fixed with a rivet and wouldn't come off. The piece I remove however, shouldn't affect it's function - I will have to eat my shirt if it does. :shrugs.

Pics, words and all that.......

To finish today, I put on more Bilt Hamer Deox Gel all over any exposed metal (just because) and the newly cleaned bits as described above.

Next up I am trying to figure out how I am going seal up the inner lip. I am in a situation where the inner arch steel and quarter panel come together and are both exposed (with a slight gap in between) due to the cutting. I think I will be using U Channel rubber to cover over along with some combination of seam sealer and filler. I will draw a diagram to show my proposal for critique, shortly.


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## conor




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## conor

By the way, whats the black stuff on the metal after the rust remover was washed off?

---

So here is something I was planning to do with the inner arch.

I forgot to add that on the internal (hidden from view) areas, there will be some kind of topical treatment such as waxoyl / dinitrol too.

Very much belt and braces, but I think it looks like a decent enough solution - I feel like the U channel is key to protected the absolute edge, because in my opinion is the ultimate flat in the original design and the most sensitive part.

Anything I can use instead of seam sealer as I don't fancy opening a tin for just than (will return it) as it seems I don't need it anywhere else.


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## grunty-motor

I personally wouldn't do the big red blob of filler incase it cracks and creates a water trap at some point.....I've seen that on arch repairs in the past but that could be poor prep work.

black stuff? Dunno? chemically converted rust? try rust convertor on it and see if it it changes

I've no experience of the rubber u clamp idea - but for sure your biggest risk of rust coming back is where the inner/out arches join (from your earlier pics, i thought that was up where the seam sealer was. If you go that route, i would certainly want plenty seem sealer in there.

its coming along nicely


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## Starbuck88

I suspect the black is converted rust from the deox gel. Still Hydrate 80 over it all. You'll find Hydrate 80 in 2 coats by brush as required will fill a lot of stuff anyway, it forms a really nice protective coating, I was surprised at how thick it dried as I have only ever used Kurust before and you can tell this is a totally different animal.

I wouldn't bother with the rubber. 

The bits where the 2 metals create that sharp edge, again hydrate 80 them and really really work it in, do many many coats if you have to, get it to creep right in every nook and cranny.

Then I'd be using Bilt Hambers epoxy mastic then Bilt Hamber UB over that, which is a protective permanent dry wax spray and then keep my eye on it over the coming years. However with the Hydrate 80, Epoxy and UB as long as the rust has been converted, should be good for some time to come!

The rubber clamp idea to me will just introduce more issues down the line.


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## SadlyDistracted

I would not put the (2k?) Epoxy over filler, it should be done the other way round, the epoxy needs to be on the metal as primer sealer (2k epoxy is impermeable) then you fill over the epoxy primer if/where needed.

As has been said wouldn't put filler in the lip, would be better with over paint-able seam sealer or stone chip. Dinitrol do a zinc stone chip, which would be worth a try.

You need to be sure there's no rust lurking in pits etc. as even though you'll covering it in epoxy, which slows it down, rust is damn cancerous unfortunately. 

Great job, stick at it and get rid of as much rust as possible, but bear in mind, epoxy, sealers, stone chip etc only slow down / bury the evil weevil when present, and help stop new damage creating more rust opportunities


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## Starbuck88

How's this coming on?


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## conor

Holy thread revival, batman!

Well, I came back here as I have new project which I will post soon. It's a full Clio 172 Cup track car rebuild.. and I fancy coming on here to share the painting side of the project.

The full build, thus far is available on the MIG Welding forum.

UPDATE ON TH SL...

So, following my last update, I ended up bringing the car to the professional I said I would. He finished off the treatment / prep work, before painting.. I am happy with the result.

Bit of a shameless photo dump, with no real explanation..


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## Andyblue

Looks like a nice job done there on the arches - hopefully will last a good time :thumb:


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## ridders66

I love these old SLs, having worked on a great many I can concur that they are terrible for corrosion around the arches, and on the bottom corner of the folding hard top, that was a weak spot too. Did you not try to get it done under warranty? We had all of ours done under the anti corrosion warranty, if my memory serves me well, and it's 12 years since I worked at that place, Mercedes had a 30 year warranty on the paintwork.


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