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Rust is the enemy of everyone restoring an older car. This is especially true for cars that spent significant time in areas where the roads are salted in the winter. If you’re lucky, it’s only surface rust. The rust you’re most likely to encounter on cars from the Seventies and earlier is more than that, though. This is where you’re going to have to decide whether you’re going to treat the rust or replace the section that’s rotted too badly to treat. I’m going to look at how to see how bad the rust is and then getting the body panel/floorpan/etc.to where it’s not going to rust anymore.
You’ve got to remove the surface scale and road grime before you can see what type of rust you have and decide what restoration options you have available. This wire wheel rust chipper is an excellent tool for this purpose.
There are three basic types of rust: flash or surface rust, rust which goes beyond the surface and rust that’s eaten clear through the metal. Surface rust can be removed with either a wire brush or sandpaper. Rust that’s eaten clear through can be obvious due to holes in the metal, or not so obvious until you test it.
If you can push a finger or a screw through the rusted section, it’s been eaten clear through and will need to be replaced. If you only scratch the metal with a tool, you can treat it to return it to a condition where you can paint it and know it won’t continue to rust.
Panels which are rusted clear through come in two flavors. Really bad panels will have holes that are obviously rusted through. Even if the rust is obvious, only testing it will tell you if it’s rusted clear through or if there’s still enough of the base metal to work with to treat the panel.
Obviously, if you can push your finger through a supposedly solid metal panel, rust has destroyed the metal. However, if the panel is questionable, I like to use a screwdriver or nail. You can have a panel that’s really rusted clear through but doesn’t break when you push at it with your fingers. It only breaks when you use a tool. You’re going to need to figure out where the rust ends and weld in a new piece to fix the panel.
You’ve got two options for dealing with rust that’s more than surface rust but isn’t rusted through. Rust that’s just a bit worse than surface rust but hasn’t started to really weaken the whole panel’s integrity can be encapsulated.
As an example, you’ve already gone from front to rear on the rear quarter panel once or twice with a wire wheel, and there’s still a sizable chunk that’s rusty but still solid. This is a perfect example of when you’d want to use a rust encapsulator, because the panel isn’t completely rusted through. The encapsulator will deprive the rust of oxygen and stop the process of oxidation.
Rust conversion is used when the rusted panel still has some rigidity but is rusted clear through. It’s not going to be show quality, but a good rust converter will at least give you a surface that can be primed and sanded smooth and is then ready to accept paint and look decent. Unless you plan to abuse the vehicle, panels and frame rails where a rust converter has been used should stand up to regular use for years.
Rust conversion and encapsulation are quite similar in usage and application (which we’ll cover in a bit), but they’re not interchangeable. A rust converter is for when the panel’s rust has almost reached the point you can punch through it. It doesn’t matter how bad the panel is - as long as it isn’t weakened to the point you can punch through it, it can be treated with a high quality rust converter.
On the other hand, rust encapsulator can only be used when surface rust can’t be removed with a couple quick swipes with a wire wheel. Rust encapsulation works best for surface rust that’s spread over a large area.
It may sound obvious that rust encapsulation doesn’t work on metal this isn’t rusted, but it goes further than that. You’d think that un-rusted sections would be protected against rust encroachment if rust converter gets on them. That’s not the case. In fact, it’s usually recommended to apply the rust converter twice and allow it to cure, then apply encapsulator over the whole panel to protect it from rusting in the future. The panel can then be sanded smooth and have a rust-preventing primer and paint applied.
Check out the picture above. Current logic has this frame section being rusted beyond hope. Not true. This is exactly what rust converter was designed to tackle. Get rid of the biggest pieces of surface rust and liberally coat it a couple times with a good rust converter. You can then sand the section, apply encapsulator over the whole area, sand it again and then paint it as usual. To convert every bit of the rust to something that’s not going to rust anymore, you may need to apply three or four coats to really badly rusted pieces.
Rust converter needing basically pure rust to work means that it’s actually more difficult to apply than rust encapsulator. Rust conversion products require that you remove every bit of paint from rusted surfaces. You’ve also got to treat bare metal that’s been exposed to it, or flash rusting might occur. Encapsulator can be applied to bare metal and paint without worry.
If you’re working on a car that’s going to end up like this one, you should probably only worry about using the rust encapsulator, and even then only when the rust is difficult to remove completely, quickly and easily. Otherwise it should be cut out and replaced.
Image credit: Wikimedia Commons
I spoke with a number of different restoration specialists and their opinion is divided. A few of them don’t believe in conversion. These guys feel that if the piece, especially a frame, is beyond encapsulating, it needs to be replaced. Most of these are guys who can point to trophies on the walls and shelves of their offices, showing their work has received many types of awards. Two of these guys convert older cars for NASCAR and NHRA racing and feel that converted rust also doesn’t give enough strength to the metal structurally.
Everyone was in agreement that if you’re simply performing repairs to give you something reliable to get around town and enjoy, encapsulation and conversion are viable options for overcoming even fairly serious rust on frames and subframes. It’s not going to cut it if you’re looking to win shows or race near pro levels. Rust encapsulation and conversion are great for the classic muscle restoration where you’ll be taking it out to cruises and maybe for meet-and-greets.
Rust encapsulation and conversion are great, but sometimes you just have to bite the bullet and replace the body panel or section. The rust may not look all that bad; it may not even be extensive. Where it’s located might be the problem.
I would think twice if you’ve got bad rust where windows are located. This is just asking for structural weakness and water leaks. Areas around bolt and screw holes where the panels or body trim attach are also prime candidates for either welding in replacement sections from junkyard pieces or complete panel replacement with something like New Old Stock (NOS) components.
Most rust converters and encapsulator products give you three options to apply them. You can buy a spray can and apply it like spray paint. This is great when you’ve got a whole panel to treat and don’t care that much about overspray.
Most rust converters and encapsulator products give you three options to apply them. You can buy a spray can and apply it like spray paint. This is great when you’ve got a whole panel to treat and don’t care that much about overspray.
