Idunno

Your statement about any of the above coatings being allies of rust lacks qualification. The preparation for employing them all is 90% of the work and that is where the pay-off comes from. If people were to believe your claim then anyone who knows about aircraft (literally all currently flying of all types) construction would never fly again, the word would get around and a new urban myth would arise.

If you apply any of the coatings over rust they will enhance the propagation because they trap the entrained moisture that's causing the electrolytic action. You have to remove the rust completely, get down to the base metal and then scarify it to give it the tooth the coatings need to grab into the metal and form a moisture-free bond. Just before applying fiberglass I heat the prepared repair area with a heat-shrink gun to ensure it's moisture free. Then I lay up the initial glass pre-preg and wait for the cure before applying additional laminations. With moisture removed from the repair area, there's no chance of corrosion to begin galvanic action.

Metal must be exposed to moisture and contamination to have the properties necessary for corrosion to start. If one were to believe that coatings were friends of rust, paint (coating) would not deter galvanic events and the metal would corrode beneath it. The only time that occurs is when a bare metal area (chip in paint) begins to rust and the rust creeps under the adjacent paint radially outward in a spiderweb fashion.

The only thing I will never use is Bondo. That stuff is hygroscopic, meaning it absorbs the moisture from the relative humidity in the surrounding air as it cures. Once cured, that moisture is entrained and remains there with no place to go, being sealed in by the paint topcoat, and ultimately begin corroding the metal surface it's bonded to. Once the bond has been completely compromised the Bondo repair will be held in place by the paint topcoat only and appear as a discontinuity in the surface (bump), because the corrosion beneath it has grown and expanded it away from the metal surface.

Rust must be completely removed before any repair can be expected to be durable, and that includes welding.

BlueRidgeMark

I'm not talking about applying over rust. Rust eventually happens to ferrous metals, no matter how well prepared. When it does, you have two choices; fix it or ignore it. The three coatings mentioned are very strong, and they hide rust until it has progressed far beyond where paint would have failed and allowed the rust to show through. Thus the inevitable rust will do more damage before it is discovered; often fatal structural damage. Thus the vaunted strengths of powder coating are actually a weakness.

I'd rather clean up and repaint a rusted surface than replace structurally unsound parts that got that way because rust was allowed to progress unnoticed.

caged

you both have good points.

yes the metal has to be absolutely clean of rust and moisture, for either fiberglass or bondo to work. yes bondo is very hygroscopic, but used in the right application (dents, not rust repair) can be very effective.

i agree with the powdercoat argument, it works great at first, till you get a chip in the coating, then rust forms underneath, doing it's dirty work before you get a chance to see it. and if you do, and decide to fix it, it is very difficult to grind that shiite off. i prefer coating my newly fabbed parts with simple tremclad (or rustoleum, for my friends south of the border). easy to spot rust corrosion, and easy to grind/repaint the effected area.

it's all in the prep. if you don't get all the rust, it will show up sooner than later. rust never sleeps.

boxburn

I like that, it's so true. It means my Jeep is... going to rust more.

BlackXJay

Sorry to stop the discussion but here is the finished product before the seam sealer

BlackXJay

Good thing I got practice bc looky what I found

BlueRidgeMark

Not long ago I looked into what it would take to remove it chemically. Pretty ugly for a DIY operation. Expensive, very nasty chemicals, and then what do you do with the waste?


Exactly.

And it's never lonely.

lawsoncl

My first thought is that you need a nice autodarkening helmet so you can see where you're welding, and a little practice on some scrap sheet metal to get the voltage/feedrate dialed it a bit better..

BlackXJay

I have a quality helmet and when practicing I did a bit better. It was just the awkward positioning and not really being able to clamp the patch down (and me not having a clue how to weld) that led to the welds being what they are. I was also trying to prevent blowing a hole through the pan. I have my lincoln 140 set all the way down with a very slow feed rate, when I turned up the speed alittle it seemed to help. Also I am using flux core for now. But hopefully it holds until I weld in a whole new pan next year, better then nothing.

country2

When I welding mine I used self tapping screws to hold in down then weld and remove screws weld hole shut.

boxburn

X2 on using screws to help but only if you can weld small holes back up.

I do that on panels where there is no access to push from behind.

BlueRidgeMark

Magnets.

boxburn

Magnets when you can, screws when you can't.

1 like to anyone who can guess the car I was welding.

BlackXJay

Well on this section I decided to use steel rivets bc of my crappy welds on the first section, then spot weld inbetween. In my opinion my spot welds were much better then the first attempt, that's the good news. Bad news is my lincoln 140 that I have only used a hand full of times will not feed wire, and I didnt get as my welds as I wanted. I'm going to have to find a repair shop to take a look at it.

caged

check to make sure your wing nut holding your wire spool isn't too tight. or that your drive wheel has the correct amount of tension.