Fighting rust, need help!

[katana]

Hi everybody,
I bought a 280SE 4.5 yesterday and started to take a very close look, poking around at some spots, and guess what: Found bondo at the back of the rear fender. I guess originating from spare tire well. Well, it's fixable...

Now, how do I get the old undercoat off? That stuff's tough...

Thanks,
Fritz

[Nate]

Well on my ford i'm using plasti kote's rust out (rust converter) which is paintable, sandable, and primable... only downside is its about $12 for a can...

For the undercoating, i've never delt with it on a mercedes, but try a putty knife (very slow and tedious)

For using the rust converter, do NOT grind down to bare metal, just wirebrush it, and then paint it... If you go down to bare metal, it WILL NOT stick.

Get the stuff thats in a black bottle, that you paint on... the spray on isnt as good

~Nate

[Tom Drew]

Having stripped both fenders on my 108, I'm well aquainted with the toughness of the MB undercoating. The best method I found was to use a heat gun and a putty knife to scrape it once the heat softened it up. This method assumes you are stripping the panel front & back and not trying to save the exterior finish opposite of where you are heating and scraping.

The other method that worked for me was to use a high speed rotary grinder or sander, but the problem with this method is that you have to be extremely careful not to remove metal along with the undercoating.

Suffice to say that even at best it is not a fun or quick job.

[katana]

Tom,
Nate,
Thanks for your input. I was kinda afraid you might say something like that. Elbowgrease time for me I guess. Have you ever worked with the por15 rust repair kit? $120 is substantial price for just trying something...
Thanks,
Fritz

[Nate]

I've only used por-15 once to clean out the motorcycle tank (been sitting 7+years)... and it worked exelent...
And I can safely say that you could do it in an hour, two hours max...
Another way is to spray it with wd-40 UNTILL you can take two hours to really deal with it... It stems the rust, but the first time it rains u gotta respray it or deal with it... Got any younger family members that are into cars? Its labor intensive but not thought critical... just tell them NOT to go down to bare metal...
Heat/scrape the undercoating with a putty knife
wirebrush/wheel the rust untill its surface rust only
paint with "rust out" (or was it rust away... forgot)
then after that drys hit it with some more undercoating

Real simple, just takes time... One hour of rust prevention prevents two hours of rust prevention in two years (say that 5 times fast )...

~Nate

[katana]

No kids... ? ??
If I had any, I probably couldn't afford to play around with a car, for several reasons...
I'll have to add a few hours for patching that hole, too. So, I know what I'm doing next weekend.
In the meantime, I still have some rustoleum primer. That should last until then.
Thanks,
Fritz

[Nate]

its a hole? I thought it was just rusted but not all the way through... For holes that dont support alot of load, use a fiberglassing kit (resin and a glass sheet). Just get all the air out, and let it sit...
~Nate

[katana]

Nate,
Just ordered the por15 complete kit with everything for $120.
Should be able to tackle most problems, including small holes...

Do you think it's worth it to dismount the fender to do the rust above the headlights? I am thinking I might get into the inside better.

Thanks,
Fritz

[Tom Drew]

Check out this post for how I repaired my 108 front fenders:

Proper Chassis Paint. Any ideas???

[katana]

Hi Tom,
Sounds like the right way to do the job. Now I'm no welder, so I'll try the por15 rust remover kit and see what that comes out like. I am pretty confident that the holes are not so big to require welding. We'll see once I have the paint off. I am not so naive to not expect surprises...
Fritz

[Tom Drew]

I believe the POR-15 kit will work if you follow the directions. The most important thing is to pay attention to the preparation details as that will determine the bonding strength of the repair to the metal. If your repair does not bond properly to the metal it won't last, regardless if your material is POR-15, fiberglass, etc.

Keep us posted as the project progresses!

[katana]

The bonding, or rather the lack thereof, is the reason I have a hole in my trunk. A previous repair didn't stick because someone tried to stick fiberglass to undercoat, with the effect that the epoxy didn't cure where it touched the undercoat. But that's not something you want to find out by poking around with a screwdriver in front of the guy you want to buy the car from. So you try to make estimated guesses...
Thanks for now.
Fritz