need education in rust
 

In general, when a late 80s or early 90s MB has a rust spot as shown in the attached photo, how bad can I expect the rest of the car to be? Is rust like this caused by an accumulation of salt on the inside of the panel or did a stone chip go unattended for too long? Should I fear the worst if I were to pull the plastic cladding to address that spot?

This picture is off a W124 in eBay.

Thanks,
Sixto
87 300SDL

an isolated rust
 

spot could be from an accident repair. it is impossible to duplicate the factory prep and so often rust results from repairs. they will particularly show up at edges and ridges where the power sanders will concentrate the sanding and take it down to bare metal.

tom w

I can sure relate to this. I've done some cheap rust repairs on the van. Sanded down to bare metal, light fill the surfact pitting with Bondo, prime and paint. Not for show........simply to stop the rust.

Two years later, rust appears in the exact same area. My feeling is that the rust remained inside the steel and it's impossible to completely remove it once the pitting has occurred.

If there are any tricks that I'm missing, please advise. I constantly chase rust on this van..........and I'm losing the battle.

I just placed an order for a kit from por-15 ...I'm going to give that a go. I've always operated under the "the more affected metal you can remove the better your chancers are" assumption....

Rust, like cancer, will return if you don't remove all of it.
There are some metal treatments that may work. Claims they turn rust into primer. I've no long term experience with them.
Anyone with POR experience?

I firmly believe that the rust preventative/undercoating on a Benz is excellent. The rust on my MB is happening in different places for different reasons, but almost always from moisture trapped against a surface, not salt. Plastic side panel mounting holes, rear quarter and floorpan rust from leaky rear window, spots behind plastic inner front fender panel, spots near front cowl where leaves blocked draining, road sand in jack points (probably aided by salt here), etc. In testament to the metallurgy of the affected metal, my rust is highly localized, unlike the huge sprawling blooms typical of domestic iron, such as my 80 Chevy pickup! :eek:

The lower cladding on my 126 is attached by metal clips. The clips scratch the paint off on the body and the body and the clip itself rusts.
It is good that most of the rust is under the cladding where a cheap repair is not visible :) but bad that the rust can't be easily seen to stop it early. :(

I have a little rust issue as well on a 95 W124.

The pic shows the roof just above the windshield seal.

http://i10.photobucket.com/albums/a1...d/000_0498.jpg


I tired resizing the pic but it didnt go too well, sorry.

Today I will go to a body shop to see what they can do about it. :(

Don't use Bondo. It absorbs moisture.

right about now I'd appreciate if someone would post something like "I used POR-15 and it reversed corrosion, improved mileage, and solved all kinds of other problems"... :D I figure in a week or so I'll have my own experience to share....

recently i repaired a significant amount of rust damage on my 90 300 te 4 matic.most of the damage was located under the lower plastic trim panels.the front of the rocker panels seems to be a bad place for dirt and leaves to accumulate.i removed with no exageration about 5lbs of crap from this area.definately recommend checking this on a yearly basis.to acheive success with any rust repair you must sand or media blast the affected area to remove any trace of corrosion getting down to clean metal.next step is an epoxy 2 part primer to seal permanently followed by several applications of a "high build" primer with fine sanding between coats.i finnish with basecoat/clearcoat to blend using a small airbrush perfect for small spot repair.this technique will give a longlasting repair that will look good from the curb. :)

Rust & POR15
 

I've been involved in restoration/maintenance of older cars for some years. I usually figure that what I see on the surface is 15% of what is going on underneath. Rust is like an iceburg. You only see a little of it from the top side.

I used POR15 on the floor pans of a car after it developed some rust due to heat/moisture over the exhaust system. It flaked off after a while. I tried applying it after wire brushing surface rust off, and I tried it directly over the rust. No significant difference. It dried thick and hard, but it had poor adhesion. I've read the testimonials, just like you have, but my experience was not consistent with their ads.

I have found exactly one solution to rust: cut it all out and replace with new metal. Grind the metal clean and clean it carefully with a tack rag. Do not let it sit before priming and prime with a self-etching primer/surfacer. As long as you do not expose any metal while blocking the surfaces, you can take your time from there on.

We would all like to think there is some majic elixer that will stop rust dead in its tracks. Again---not in my experience. After replacing most of the bottom half of a car that looked pretty good from the surface, my reaction to rust in any prospective purchase is to RUN AWAY.
Mark
93 300D 2.5 turbo
99 Crown Vic Police Interceptor
61 R-R Silver Cloud
66 Mustang restomod

I've used POR15 on one small spot and it seems to be holding up well. I was unable to get it deep under the window seals where the rust seemed to extend, so it is not a thorough job. On the other side of the car is the biggest rust patch, which I sanded with a dremel and slapped on one coat of POR15, but never got the chance to put on the second coat. The first coat is no good now because it's been exposed to sun too long, so I just need to start over. Couple things with POR15 ... leave a small amount of rust because the stuff adheres to the uneven surface better. Use Marine Clean first, then Metal Ready, then POR15 and do two or three layers. I've only had it on that one spot since about March (April maybe? I'd have to check my records), and it's done well so far.

The best way to stop it is to replace the area, as several people have pointed out. That said, I would think an uneven or lousy job could create a situation even more prone to rust.

If you're looking to slow or temporarily stop the problem, I recommend POR15 ... it doens't look great but it buys time.

I'm taking my 124 to a trusted body shop this week. I simply do not have the means to do the POR15 job I want to do (no garage, bad weather, little time), and I can't just let the car get worse and worse while I wait for the right conditions to do the work myself. The guy I'm taking it to is very good, and also will be cool about helping me attack it in the most affordable yet functional way. Hopefully the price tag won't be out of my range. :( I can't let the situation get any worse.

bondo and moisture
 

I agree with Mr. Delano from a few posts back. You cut out old rust, put in bondo, it gets wet and traps water. Then contact point of the bondo and metal rusts out in a ring.

A friend of mine put himself through college in the 70's doing rust repaints in Buffalo. I was the "works for beer" guy who hung around trying to learn his tricks. His technique was to cut out the rust and form a new panel of galvanized sheet metal as a patch. He would overlap the good metal by about 1-2". He would then use a brick behind the metal as a form and hammer to make a small divet or indentation in the overlap area along the seam. The rivets went in divet so they did not show. Bondo in the small overlap area / divet only to cover the seam / rivets. Roofing tar or undercoating behind it to prevent moisture from getting in. A gallon of Dulux enamel and the car looked great for a couple of years.

Chuck

I have used a product called Rust Bullet to hit a small rust spot in the rear wheelwell. It's supposed to be just like POR only with much better adhesion. It's best to get both sides of the affected areas also. Otherwise the rust keeps right on truckin'.

Rust changed to primer.....
 

There is a product to change rust to a primer type surface. I did this repair to my 56 Nomad wagon back in the 70's. Really poured the stuff on after removing all loose surface rust. Then did it again 2 more times. Back side covered with a fiberglass/roofing material.....allowed to harden and then painted with a flexible epoxy paint on the backside at the last of the repair sequence (as best I could...not being the best contortionist in the world). Then, on the outside, stepped the metal down and welded in home made pannels of galvanized metal. Then on outside, just as little bondo (ALL STEEL -type or brand name if I remember correctly) as possible. Again, an epoxy primer and paint. Has been 30 some odd years. Seems to be holding, but for how much longer????????

Regards

Run-em

theres no doubt if the metal is perforated it must be replaced.cut out the area carefully with a dremel.use the removed piece as a template to fabricate a new one.if you trace around the old piece with a pencil and cut out with the dremel the new piece should be a close fit.the best and most rust resistant welds are butt welds.avoid overlapping the patch as this creates moisture "traps".a hobby size wire feed welder is perfect for creating the small spot welds required.a series of numerous small spot welds will hold the patch in place securely and require little grinding.finish with a super thin coat of bondo,sand and paint accordingly.Sounds easy doesnt it?a little practice will make you an expert. :)

After seeing some amazing rust on my 300SD I have come to the conclusion to avoid it all together. So any MB I buy next that I plan on keeping for awhile I will buy from a rust free area of the country. Then I will just not drive them in the winter.

Rust is like a cancer if you see a little spot that is only part of it.

Brian your mistake is using Bondo, you need to treat the rust with some sort of rust converter. Then use a filler that doesn't absorb water like Dura Glass.

If the Bondo is primed properly and a finish coat is added properly, how does the Bondo absorb water?

I think the constant bashing of Bondo might be erroneous. Water can't get beneath the paint and above the steel panel. The rust must be returning from within the steel. This is where a proper converter might be of assistance, if it works.

Sure water can get below paint in the marine world this is quite common.

Bondo is made out of a type of epoxy that absorbes water, people who fair their keels and outdrives with it get nasty surprises in the fall.

Dura Glass is a body filler made for cars with fiberglass body's. But it doesn't abosorb water and can be used underwater.

How does it get below the paint on an automobile, unless the topcoat(s) are compromised?

I'm sure it gets through paint isn't water proof like it appears.

Actually I know of a boat that had Petit Easypoxy applied to dry lockers a year ago. The owner placed a little wet gear in their but nothing that wet. Guess what under neath that stuff the paint is lifting and is wet.

You perpetually refer to boats........wooden structures that are surrounded by water and gratefully absorb it.

I'm betting that the paint on an automobile is waterproof. If it was porous, every steel vehicle out there would have rust all over the body.

Too bad there does not seem to be a corrosion engineer on our site. Most short hair and long hair auto body filler is waterproof to the best of my knowledge. Normal bondo just absorbs water (hydroscopic I believe) if given the opportunity. Plus remember that laquer based primers let moisture through although I believe top coats or two part primer are waterproof. The iron rule though is not to bury rust. For if you do it will cause problems sooner or later. There is a specific surface rust rhat occurs on mercedes products that should respond to sand or media blast and metal prep before finishing area quite well. Also rust seems to be somewhat different depending on your geographic location. Same thing but just develops differently and to greater or lesser extent. I consulted a corrosion engineer years ago for a business. He said basically nothing really stops the oxidation process other than removal or true conversion to iron oxide with things like phosphoric acid. He was full of ideals on how to slow it up though. So unfortunatly the comparison of rust\cancer does bear some truth it seems.

Rust and bondo
 

The problem with bondo is that IF there is any moisture around, it WILL absorb it, then trap it next to any bare metal. Often the moisture is present before the paint is applied. Sometimes, filler (bondo) is used in places where moisture can enter it from the back side. I have a car that has parking lamps set into the tops of the front fender. The housing for them was originally leaded on to the fender (another story), but a restorer welded them and filled around the edges to smooth. The wire lead for the bulb came through the back of the fender into the housing--protected by a rubber grommet. It leaked. Moisture entered from the back and was absorbed by the filler. It turned the metal beneath it into rusty lace. From the top, the only visible evidence was bubbling at the edges.

Filler, used very sparingly, is OK--even necessary sometimes. Some shops use tons of it to cover all sorts of demons--including old rusty areas they did not want to take the time to fix.

Also: Paint is not an impermeable barrier. It breathes and moves with changes in temperature/humidity. When it gets old and has been exposed to years of UV, it cracks. Moisture creeps into amazingly remote places. Trapped there, the inevitable happens.

i realize this is not a restoration forum, but the principles apply to rust repair, generally.
Mark
93 300D 2.5
99 Crown Vic Police Interceptor
66 Mustang Coupe (restomod)
61 Rolls-Royce Silver Cloud II

i agree totally with the above post
 

and to emphasize, it is ok to use bondo on the surface of sound metal. as noted above any perforations will allow moisture to come in from behind.

for any areas with perf. you must use the fiberglass filler or metallic.

if i have rust to repair, i sand it and cut out as much as possible, rust bind it and sand again, and rust bind again, then prime and paint. as much of the rust must be removed as possible for a good job.

tom w

http://ptcl.chem.ox.ac.uk/MSDS/glossary/hygroscopic.html

Newly sandblasted steel in a humid warm climate will show rust 10 minutes after being blasted. Before painting one must be sure the dust is off a piece...which usually means using the air nozzle... one must be sure that the air coming from the air source is as dry as possible... this needed to be the case for use with painting equipment and air tools anyway.... so care should be taken to really get it dry.
An extra cooling/drying tube arrangement is often worth the price... the little air filters coming off the air compressor are just the starting point.
Sandblasting is the ideal surface for the application of Bondo since this is a physical bond process compared to chemical. If you do it in a temp/humidity controlled space and apply it immediately.. then work it as soon as possible and apply primer you are in pretty good shape.
Primer is hyGroscopic. I laugh everytime I see cars driving around with primer on them.... the people did a great job of sanding.... but failed to read any books about Auto Painting...
I do think that properly applied Top Coats of automotive paint are water proof. Those long chain linking molecules are amazing....
The problem when painting a car is that primer ( which includes what is called ' spot putty ' .. paint with little carrier which is applied with a rubber squeegy ) absorbs THINNER, REDUCER, ( whatever you want to call the carrier liquid ) ... so IT EXPANDS with each primer coat sprayed ( and when the top coat is applied )....
so you really want to let the primer dry for weeks before applying the top coat.(also wait on top coat sanding) But that way you are leaving it exposed to the weather even inside unless your paint stall is temp/humidity controlled.
If you sand TOO EARLY then that expanded area which is slightly thicker than other areas will be LOW when it DOES get rid of the carrier.
I have tried and read about the rust converters... I do not trust them. Some may convert but still leave less than solid gripping surfances for the next coat. I don't know of many places on a car where butt welding is the best replacement choice. Too many places won't allow welding at all due to the insulation and bad stuff behind it or close enough that you can't really use big heat. Cutting out , flanging the sheetmetal with an air flanger, putting holes for both plug welds and rivets ( applied first ). In most intances the rivets done alone will be great ... and it means you can apply something like POR15 to the area after you have drilled your rivet holes...and put the thing together using the POR15 as a sealer between the old metal and your patch.
Before someone says something about rivets... remember that they put Airplanes together with them.... there are no doubt more kinds of rivets and more instructions about choosing and placing them than you are aware of.

great post greg
 

yeah, i have used rivets many times. usually when done you can't see them, but if the car is just a driver for a new teen driver i have left them exposed on occasion as a neatly painted patch with matching paint is a lot better looking than a gaping rusty hole.

knowing that the odds of a new driver having a wreck are exceedingly high i never put too much work in the body til they had a year or two wreck free.

tom w