Seam Rust

[hotrod1]

I have been pulling apart seems by cutting out the spot welds. Once you do this and separate the seam, they all appear to be rusty. Every one. I am sure that this is common with this type of construction. They are filled with rust. Thought about trying to get POR 15 in there.

What have you done with seams that you have not pulled apart?

[Virginian]

Nothing, other than seal them off from moisture, but mine is not going to be a show truck,it's a driver.

[OrrieG]

Grind them out with wire wheel and 1/16" disc, use rust converter on both sides, prime and seal exterior; prime, seal and undercoating on the inside if I can reach it.

[hotrod1]

Thanks OrrieG. I am referring to the seams that are spot welded together but you know there is rust in between them. There is no room to get a disc in between the seams. I just know that my truck was painted quite some time ago and those seams are seeping rust. My truck is from California and has spent most of its life indoors and there is still rust seeping out.

[Foot Stomper]

Which seams are you talking about? Can you post some pictures?
To over simplify, rust needs oxygen and moisture to continue. Stop both of these and you have your solution.
Cavity wax has a fantastic ability to creep into impossible to reach places and will displace moisture and seal off oxygen and its easy to apply. It's a bit messy, drippy and doesn't dry and will attract dust and dirt. Even axle/bearing grease could be your remedy. Both of these options would be a far better solution and much easier to use than POR 15.

[msaintg]

I tried to eliminate all metal to metal spot welded seams where possible. for the stake pockets I cut the old mating surface off, undercoated the backside, and welded back on. For the tailgate, I just completely built a new one. I have seen guys weld up the cab seam, but you cant get in there to clean and seal it.... usually not that rusted anyway.

[1project2many]

Here's another thought that catches most people. Rust is the end result of iron being exposed to oxygen. Bare steel rusts very quickly but steel with a coating of rust continues to rust much more slowly. The reason we remove surface rust in many cases is so a coating will stick, either for appearance or more often for protection against moisture and oxygen. If you find a method to seal the seam and if you can determine the seam doesn't need mechanical repair, then you can seal the rust in and it will not progress.

I have used acid to clean many rusty surfaces. Phosphoric acid is used in most rust converters. It will change rust into a form of iron oxide that is more stable and better as a protective coating. It doesn't work with with deep rust but it works very well with surface rust. Hydrochloric acid strips steel down and leaves it bare. Because they are liquids they can sometimes be used where mechanical rust removal will not work. Before using acid you shoud obtain hand, eye, and skin protection, and learn the precautions needed to use acid safely. You should not use a base to neutralize the acid after treatment as the base will tend to oxidize steel and start rust.

Paints that dry but do not cure can be used with some success inside panels and in hard to get to places. Single stage urethane paint, often sold quarts and gallons to be applied with brush or roller, is more durable and allows considerable work time before it cures. These paints can be thinned and worked into seams or other areas. Waxes, greases, and oils as mentioned above work well but they cannot be painted over. Most of these products soften with heat and some have quite an odor when they are warm. Commercial sprays sold as "interior panel rustproofing" are the same wax mentioned previously. Seam sealers are great for high traffic or high exposure areas. I will use urethane sealer available to the building construction trades. It's cheap, can be painted over, and it's dang tough stuff. Use gloves because it adheres to surfaces very well.

Finally, if you really want to learn about rust prevention, spend some time reading forums populated with people where it really rains. This is one of my favorite threads to link to: Rust prevention in India. Even if you don't use any of their suggestions (multiple baths in diesel fuel???) the job ahead of you will seem much more manageable by the time you're done.

[Foot Stomper]

When two panels are being welded together, it's imperative to use zinc or copper weld thru primer. These products will prevent rust better than anything else and are the easiest to weld. Most folks will put too much on, won't wait for it to dry or buy the cheapest product and use it once or twice and then refuse to use it again, then go back to welding bare steel because it welds far easier than steel coated with zinc or copper. These products will help to keep your spot welds smaller too but the main thing is they don't burn off leaving a large area of unprotected metal between the panels.

If you're butt welding, this product has zero purpose. It's only meant for welded overlap.

[hotrod1]

Here are a couple of pics.

An overlapping seam was taken apart to find rust. You are right that it needs oxygen to really start rusting but I have seen rust creeping out of these overlaps causing rust discoloration of paint. I would like to stop this from occurring. Also see a cut apart overlap to see what is really happening.

[BlueJeep]

That's what made my project take way longer than I wanted it to.....

On mine I made a judgement call. If the rust was swelling the seam I cut it apart and cleaned it and put it back together. Some of the seams I used weld through primer, some I used POR 15 and then ground clean where the spot welds went, and some I left bare and relied on my seam sealing and epoxy primer to take care of. In my opinion, you have to decide how deep you want to go and stop there.