Best repair of rust bubble

[JHZR2]

This isnt my car but it is an old MB diesel that I have interest in seeing survive.

Bubbles through the paint mean worse on the on the backside I assume, but is an item like this (front fender so can be removed) worth repairing versus just replacing with a good used one?

If removed and repaired, I assume the best bet is to figure out how to blend the paint, but paint and bake off car to get the best paint cure (versus baking an entire 30 year old car)?

Thanks!

 

[maxdustington]

100% rust removal involves sand blasting and acid treatment, I did the same on a set of fenders on my car and it's held up for two years now without coming back in the rust belt.

Take the fender off, blast that area to remove scale, acid treatment to remove the rust from the pits and then maybe another blasting session until all you see is metal. I had to wet sand the clear on my fenders because it was way easier than blending the clear. If the area is just dirty and not hiding a previous repair, that's a small rust spot that can be fixed easily by a DIY without any special tools (I used rattle cans, a hand held sandblaster with crushed glass and Ospho for acid).

 

[Warstud]

Originally Posted by maxdustington
100% rust removal involves sand blasting and acid treatment..


Not necessarily those ways but rust removal however you do it. And I don't think fender removal is required for that job.

 

[maxdustington]

Originally Posted by Warstud
And I don't think fender removal is required for that job.
I'd rather just remove the fender than mask the entire car and wheel off personally, with the additional bonus of being easier to work on. Because it is close to the edge of the panel, there could be hidden corrosion around the edge under the paint. If that blemish that is seperate on the fender flare is rust, the problem is probably worse than it appears on the surface.

 

[MasterSolenoid]

Take the Fender OFF ? - I don't have that much ambition.

If the rust does NOT go thru the metal:
I would scrap the rusted area very carefully using a scrapper with a sharp corner.
Keep scraping until you get 99% of rust off.
Use some type of rust neutralizer and self-etching primer.
Then a small paint brush with a matching color.

Hole rusted thru:
I would cut a metal patch 10 times bigger than the hole (4" x 6" min) and
rivet it on. If you use two rows of rivets and stagger them,
it will look like a Bus or Airplane.
Sit back and wait for the compliments

 

[Nick1994]

Id think you can just grind/sand it down to bare metal, use some filler, sand it smooth and have it paint matche d any competent body shop can match it close enough.

But some people freak out when they hear of filler being used. Oh the horror!

It really isn't a big deal.

Then afterwards use some good paint and undercoating on the back sides of the fenders to prevent more from happening.

 

[SatinSilver]

Looks like it's been repaired at least one other time and bubbled up again. I'd remove fender as others have mentioned and start the repair from there. I'm sure Trav would know how to properly fix it since he's talked about the issue before.

 

[Andrew1972]

Originally Posted by SatinSilver
Looks like it's been repaired at least one other time and bubbled up again. I'd remove fender as others have mentioned and start the repair from there. I'm sure Trav would know how to properly fix it since he's talked about the issue before.



Yep no matter how "good" the repair work in past the areas bubble.

 

[Ducked]

Originally Posted by maxdustington
If the area is just dirty and not hiding a previous repair, that's a small rust spot that can be fixed easily by a DIY without any special tools (I used rattle cans, a hand held sandblaster with crushed glass and Ospho for acid).


Not heard of a "hand held sandblaster" before. Do tell. Sounds...er...handy.

I saw industrial sandblasters in use when I worked in a shipyard, but I'd probably have to class them as special tools, plus you'd need a big hoover to clear your MB remains up after use.

OP, perfection is nice but it can get in the way of actually doing something. The good news is that you've got a silvery paint finish so aluminium won't be too big a contrast.

I'd abrade with aluminium, using sunflower oil or alkyd resin as a binder. For that I'd use a bit of arrow shaft packed with aluminium foil in a drill chuck, finishing with foil by hand. If I was somewhere I knew where to get them I'd use an aluminium roofing nail.

If you don't like the look of it you can finish it "properly" later. Meanwhile you've slowed the rust right down.

 

[HowAboutThis]

What results so you want? Like new? Or stop the rust? Grind it, sand it, use the acid stuff you can find to remove rust you can't see, go to Napa or some place with paint code to get spray paint of the color, tape off headlights and spray with primer, color, clearcoat. It'll look decent. Or once you start your might realize a new fender is the way to go.

 

[JHZR2]

Originally Posted by Warstud
Originally Posted by maxdustington
100% rust removal involves sand blasting and acid treatment..


Not necessarily those ways but rust removal however you do it. And I don't think fender removal is required for that job.


Thought process with removal is that the part can be fully repaired, coated inside and out, and baked at higher temperature than a car in a booth. Maybe I'm wrong though?

Originally Posted by HowAboutThis
What results so you want? Like new? Or stop the rust? Grind it, sand it, use the acid stuff you can find to remove rust you can't see, go to Napa or some place with paint code to get spray paint of the color, tape off headlights and spray with primer, color, clearcoat. It'll look decent. Or once you start your might realize a new fender is the way to go.


Per above. Baked, matched high quality refinish. It's a nice, very low mileage w126 so has another 250-300k miles left based upon the reality of these cars.

 

[rinkevichjm]

That sounds like you'd see it and it would be more noticeable than Bondo. Like this: https://www.youtube.com/watch?v=fRPEDZ7Q3vM

 

[spasm3]

If you are going to spend the money to have a shop paint it, i'd pull the fender and see how much rust is really there( there is always more).

If the car is pretty nice, like you say it would be worth derusting the panel and rust inhibiting the back side. How much is a new fender btw?

 

[maxdustington]

Originally Posted by Ducked
Not heard of a "hand held sandblaster" before. Do tell. Sounds...er...handy.
https://www.princessauto.com/en/det...ed-abrasive-spot-blaster-gun/A-p8140709e It's on sale right now in case you want to pick one up

. 30 gal compressor and an inline desiccant dryer: https://www.princessauto.com/en/detail/in-line-desiccant-air-dryer/A-p8105470e That's all you need other than PPE for small projects like this.
Originally Posted by JHZR2
Per above. Baked, matched high quality refinish. It's a nice, very low mileage w126 so has another 250-300k miles left based upon the reality of these cars.
Do they bake paint anymore? I thought it was just enamel that had to be baked and then cured. If that's the case, find a rust free fender and get it painted if necessary. I'm not sure what the value of these cars are, but I'm sure you can find an original paint matching fender for cheaper than a professional repair of the existing. You could probably just let it rust for a while longer without any concerns while you wait for a suitable fender to become available. No point wasting money on a rust repair of an area for a second time.

 

[Ducked]

Originally Posted by maxdustington
Originally Posted by Ducked
Not heard of a "hand held sandblaster" before. Do tell. Sounds...er...handy.
https://www.princessauto.com/en/det...ed-abrasive-spot-blaster-gun/A-p8140709e It's on sale right now in case you want to pick one up

. 30 gal compressor and an inline desiccant dryer: https://www.princessauto.com/en/detail/in-line-desiccant-air-dryer/A-p8105470e That's all you need other than PPE for small projects like this.



Don't have a use for one, nifty though it looks to be.

Don't have a compressor or anywhere to put one.

I need a shed (not the car, an actual shed, for pottering about in.)

 

[Schmoe]

Something that small....drill it out and get to clean metal. Primer spray it. Touch up bondo, then use touch up paint. I'd be more concerned it this was the tell-tale sign of things to come in the future. Most rust would start in the bottom of doors or behind wheel wells and with that car being in N.J. may start getting worse pretty soon.

 

[Gasbuggy]

Speaking of old, that tire...

 

[Trav]

Originally Posted by JHZR2
This isnt my car but it is an old MB diesel that I have interest in seeing survive.

Bubbles through the paint mean worse on the on the backside I assume, but is an item like this (front fender so can be removed) worth repairing versus just replacing with a good used one?

If removed and repaired, I assume the best bet is to figure out how to blend the paint, but paint and bake off car to get the best paint cure (versus baking an entire 30 year old car)?

Thanks!


I do a lot of that sort of work, depending on the car and the $$ determines how much gets done but that spot possibly can be repaired properly without removing the fender although you may want to pull it because there is probably some rust lurking in the lower section by the rocker inside.

A few comment need to be addressed.
Baking (usually by infrared these days on single panels) is not always necessary and will not prevent further rusting, it adds a little durability that's all, a good quality acrylic enamel on this single stage paint car works well.

Bondo of any type over repaired sheet metal is guaranteed to cause the paint to bubble again regardless if its baked or not in most areas of the country. Filler is talc based and absorbs moisture like a sponge, even the smallest pin hole in a weld is more than enough to allow moisture from the air in. So how do you fix this? There are a couple of ways to do this properly one obviously more expensive and difficult.

Grind that area down to bare metal and give it good prodding, if it goes through remove the fender, if not remove the light and drop the bumper down and cover it with a welders blanket or other thick moving blanket to protect it and cover the rest of the car.

Blast the area and if no pin holes appear give it a 5 min acid wash (5% vinegar works well) rinse and blow dry.
Prime it with 2K epoxy primer, if any filler is needed for pitting now is the time to apply it, finish smooth and apply 2K again if filler was used then a 2K poly primer.
Block wet sand and paint.

If its a high end or collectable or you just want to do it 100% remove the fender and strip it front and back, do not blast the whole fender as it can distort.
Probe any pitting and blast those areas front and back, if any holes are found they will need to have sheet metal welding in which is a process in it self.
Once its been welded it can be filled with real lead front and back and the front filed (good luck finding someone to do this, I learned it from an old timer 35 years ago and really don't like doing it because of the lead) this will outlast you and the car.

It can also be filled with conventional filler after 2K priming, I usually cover any weld seams with JB weld then grind if off to insure there is no tiny pin holes before using the epoxy. Refinish with 2K epoxy, poly etc.

 

[maxdustington]

Wow Trav, so bondo absorbs moisture and welds are more susceptible to rust and need to be sealed?

Used fender time! OEM paint is more desirable than perfect colour match.

 

[Trav]

Yes it sure does, fillers even the so called metal ones are talcum based with a polyester carrier and sometimes other fillers like fiberglass stands or aluminum powder.
Sometimes when you pop those bubbles in unbroken paint water comes out. It got in there from behind and filler absorbed it. Regular primer is also talcum based and will absorb moisture.

Prime bare steel with primer and don't top coat it and you will see the metal begin to rust in a couple of months depending on the conditions, that's the reason for the E coat under the primer.
When you weld a patch in you must cut all the rust out so the rust is gone but welding patches can be tricky and that's where the problems can arise especially when dealing with newer cars that have thin sheet metal.

You start by holding the panel to the body with pins or tack welds (back in the day when the metal was thick and heavy we just had someone hold it with a screwdriver while we tack welded it) then weld in short sections as not to warp the metal around the patch.
A pin hole or two is inevitable, you probably wont see them without a light from behind, these are the culprit and a guaranteed failure, this is the reason people say you cant fix rust it will always come back.

After grinding the weld if you use JB weld on the weld seal only (does not absorb moisture) you just cured it, grind off the excess and prime it with 2K epoxy primer and let it cure, the rust will not come back and if you can protect it from the rear all the better. If you have access JB weld the inside of the patch seams as well if not a high quality protective coating applied with a wand will suffice.

Put the filler over the 2K epoxy and apply 2K epoxy over the filler, now you have sealed it. You don't have to block sand the 2K epoxy you apply a 2K polyurethane primer over it and block sand that then paint. In the USA there are primers labeled 2K poly which is spray filler and 2K Urethane the one I use is the 2K Urethane which is polyurethane.
The filler I like best is the Evercoat Rage Ultra if I don't feel like pick, dolly and file with skim coat of lead, the last car I did that way was a 66 Jag XKE nose and rear quarters for a restorer.
Pick and file with lead doesn't work well on thin sheet metal, its more for very old cars being restored these days, it is very time consuming and can be hazardous for you health so its not an OJT thing, you need someone to teach you.