Home Projects News and info Contact About me

Mercedes Benz 320cdi

Restoring the rear fenders and painting them

Part 1: The left fender.

At first glance only the wheel arches needed work, as you probably suspect it didn't stop at that! This car keeps on having surprises which were not expected. Again, this is a Mercedes built at the end of 2001! I just can't get over how bad it really was.

Anyway, to get some more working space to do the wheel arches I decided to take the rear bumper off. Look and see, or should I say look and shiver?

This chapter will be split up in different parts because it is going to be the longest to this date. So here we go,

*Note: Use the "hamburger" icon at the right to open the page navigation menu.


Well, yes, this was the visible part of the problem. Not rusted through so it seemed to be an easy job.

Grinded the rust as far out as possible and treated it with POR15. POR15 is like Hammerite but then specially designed for cars. (POR is an abbreviation meaning Paint Over Rust).

Actually, this doesn't look bad at all.

So I wanted more freedom of movement to get those arches done, took the rear bumper off and this is what I found at the drivers side!

I'll give you a look from the inside as well.

There is just nothing left! Let's have a look at the other side.

Nice huh? NOT! Everywhere you see a rusty color the metal is in fact totally gone. We'll come to this side in part 2, in this first part I'm concentrating on the drivers side.

Where do I start? There is rusted metal everywhere.

Well, I had to start somewhere and I decided to fix the bottom first. Took my grinder out and cut away everything till I had healty metal to weld to.

I had some .75 millimeter steel laying around which happened to be the same thickness as the original steel. Started to shape it in form.

Had to test-fit it like a million times but eventually I got it right.

Imagine I don't have all those sophisticated tools to stretch, shrink and bend the steel, Just a set of body hammers and some dolly's, an anvil, a vice and a piece of 2.5" scaffolding pipe. Oh, I got a flangetool as well.

Before I even thought about welding it in place I treated the steel with zinc-primer.

As you probably noticed there is a big hole in the new piece, that's where the drain goes but I can't put it in as it is, it needs to be at an angle. More fabricating to do.

This is the raw version, in the next photo you see the finished product. Welded it in place and called it a day.

Although the first piece is in there is a lot more to do. Cut out the next section and hammered away to get the new steel in shape.

It left me with a big hole. I did go through some rattle cans of zinc primer, about 12 of them in this total project. The big advantage is you can weld through it while it's conductive.

The second piece ready to be welded in. Hand formed mind you.

Welded it is! here you have a look at the inside.

And this is how it looks on the outside.

This piece had to be replaced and re-fabricated as well. It looked fine but once I tried to weld to it all I created were holes. No way around it but making yet another piece.

And here it is, held in place by a vice-grip.

Yep, that corner had to go as well.

Leaving me with yet another job of fabricating.

Making a perfect fit is mandatory, it makes the whole structure stronger and it helps to prevent water from entering. I will finish it off with seam sealer but that is not designed to keep those pieces together.

I do it right or not at all, that's my motto.

We're almost there!

Welded this last piece in place.

Sealed up all the seams after cleaning up the welds. Finally it looks like it should have done in the first place.

Sealed from the inside just as well.

And then, in the end, it looks like this. I used some satin black paint because the inside is never high gloss. Now I can finally start on the wheel arches on this side.

Taking the grinder to the arch was one thing, being lost in a large cloud of dust is another one.

Somebody thought it was a good idea to put like half a gallon of filler on the arch! I tell you, I was not amused to say the least!

Took the wheel off and did it the right way. Just a skim of filler is doing just as well, actually a great deal better. Things like professional carpainters call "shrink back" is less likely to happen this way.

Uhhh, yes, in case you wondered, this all is just a hobby! I'm not a professional at all in this line of work. I studied electronics but was a born car fanatic. I just can't let anybody else do things on my cars for me, I just have to know and do it all myself. So there you go, now you know something about me.

For this moment we'll leave this side alone just to discover the horrors at the other side.

Part 2: The right fender

The passenger side turned out to be even more work, I will skip details in this part otherwise it gets far to long. First, let's see what was behind the bumper on that side.


Well, what can I say? Let's take the vent out and start tapping to see what's left of it.

You're looking at the bottom from the inside. In the picture below is what's left of this part of the car after gently tapping it with the hammer.

I just took the grinder and removed it all.

There is even a part against the chassis rail that's rusted through.

It's just the same old routine to produce new pieces, this is the first one.

Welded in.

Made the opening for the ventilation grid.

Re-produced the lower part.

Now there is still a huge gaping hole it's better to do the part that's against the chassis rail first. This side sure doesn't look good.

On the other side, under the car is the tow-bracket.

This steel is 1.5mill thick, so I reproduced it using the same gauge of steel.

Zinc-primed and welded, this is the underside of the car.

The inside, I could grind those welds flat but this part of the car is never to be seen again so I didn't bother.


The other pieces primed and welded.

This is how it looks at the outside. Yes, I still have to make that corner.

Of course I made a piece for the bottom against the chassis-rail.

Only this hole at the back left to be filled in, I thought!

And there it is.

And this is how it looks from the inside.

Then I discovered rotten steel at the back end of the wheel arch.

And rust behind the rear mudguard.

And a substantial hole in the inner fender. It just doesn't stop!

Cut out all of the rotten steel and once more started to fabricate panels.

But first I wanted to treat the surface rust behind the rear wheel. Brushed it up with a wire wheel.

And then treated it with this stuff.


It contains some nasty chemicals although it is water based.

After the process was completed I sprayed it with good old zinc-primer. This part will get a new undercoating rather than just paint.

Now the new pieces of steel were made, I test-fitted the first one. Beautifull!

As well as the one that goes at the inside of the fender.

Yes, this piece. Trimmed, shaped and primed.

Welded in yet another piece, it's never ending!

Sealed all the seam up.

After welding the inside I sealed that bit up as well. It doesn't look as tidy as the rest but I had to get in a very awkward position to get to it.

And finally the fabricating and welding stages are done! Hurray!!

Looking at the right rear corner of the car. Once this receives a new undercoating you'll never be able to tell it's been repaired.

A last look at the inside before it gets covered up by the sound isolation and plastic panels that go there.

Now I can concentrate on the wheel arch and some minor scratches and dents in the fender.

Scratches like these.


With this picture part 2 has come to an end.

I'm very proud to say there is absolutely no fiberglass used throughout this restauration. Fiberglass is fine for boats but cars are made of steel and it has to stay that way! Unless you own a Corvette that is.
Don't fill holes with fiberglass, if you can't do it the proper way yourself then spend some money and have it done by a professional!

Next up is 2K primer, basecoat and clearcoat.

Part 3: Painting the fenders.

Now all fabricating and work to the arches is done it's time to put some paint on it. Of course I will put 2 layers of 2-component primer over the repaired area's, those 2 layers will be blocksanded to get a super smooth finish. Although I liberately used zinc-primer on all treated and fabricated parts I have to be absolutely sure there is a strong, resistant base before I'll put any color on it. If there would be a problem putting this primer on it's far better to solve it now as doing it to the real paint-job.

How to spray-paint a car, using a spraygun, which products to use and which ones you absolutely should avoid, as wel as problems that can arise in compatibility of different sorts of paints. All those subjects will be discussed in a separate page which will be found in the How-To section.  May not be for tomorrow but be sure it's coming!

So it's primer time but first of all I have to mask off the rest of the car. Even before I started I sanded everything that has to receive primer using P180 dry sandpaper. That primer has to have something to hold on to which is not going to happen if you don't prepair the surface.

Took the taillights out and started to mask it up.


Yes, I love to use plastic because it's very easy to handle and it's static, it will "stick" to the car. Don't use just any plastic, this is specially designed for painting cars. It's got it's disadvantages as well but again, I'll make a chapter about spray-painting a car covering all of that as well.

Ready to go!

Note I didn't use plastic to block up the vent opening but a piece of old newspaper. Or oldnews paper? Why? Because it absorbs the paint while plastic won't. If there is a solid background or the space to cover is small enough you can use plastic, in all other cases use paper. Again, details will be in the How To section soon.

And there is the first layer of primer.

Yep, other side as well.

I'm using a DeVilbiss FLG5 spraygun with the 1.8mill needle for primer. Hooked up to an 200 liter, 4HP  compressor with an airdryer inline. The compressor delivers 8 cfm which is more than enough for this spraygun.

The second layer, applied 20 minutes after the first one. This already looks nice!

Detail on the other side, results like this are all in the prepwork.

After like 24 hours I started to blocksand the primer using P400 dry sandpaper. Pay special attention to how I feathered the primer out to the exsisting paint.

Then two layers of basecoat.

After half an hour followed by 2 coats of clear. In the upcoming How To I will also explain how peeling clearcoat can be avoided.

On the D-pillar I created a blending area, this has to be wetsanded and buffed / polished to get a flawless transition.

And yes, I got a run. Nobody is perfect and since my name isn't Nobody I did make a mistake. My own stupid fault, when it occured I knew I did it wrong. Not to worry though, this run is only in the clearcoat and can be sanded out. I used a very hard (wooden) sanding block starting with P800 wet and dry sandpaper.

Sanded down somewhat further with P1000 wet and dry.

Switched to P1500 at this stage. The trick in this is you have to have a very hard sanding block so you'll only sand down the run, not the clearcoat around it because you have a very big risk to sand through it. That will eventually ruin your paintjob and you have to sand the whole panel down to give it a new coat of clear.

Yet another step up, switched to P2000 sandpaper and got the run completely out! Sanded the rest of the panel as well so I can buff and polish it.

After buffing and polishing it looks like this. I did not go through the 3 stages of polishing yet, just the first one.

After that I put the taillights back in as well as the ventilation grids.

Sure enough the sound isolation had to go back at the inside, along with some control modules for the telephone and navigation system.

The rest of the interior will be discussed in another chapter.

This is the finished product, it sure took long enough to get a result like this.

How nice is this?

Be sure the paintjob is just the icing on the cake, if the preparation is no good the result won't be either.

This concludes this chapter, like I predicted it's the longest one on this site up to this date. Hope you enjoyed it! If you want to leave any comment about whatever please contact me at Carfiles@mail.com.

Last update : August 22st, 2017
× Go to top Left fender Right fender Paint

Page navigation