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Rust treatment: How to neutralize car corrosion

Mechanic examining rust on vehicle partCar rust starts with a benign-looking bubble and grows, like the malignancy it is, into a metallic carnivore with the potential to consume a Hummer and then go looking for dessert. It's rust, the bane of anything metal and one of the greatest challenges for auto restorers.

No one is truly safe from car rust. It first rears its bumpy head in regions with high rainfall and urban areas where salt is used on icy streets. But even high humidity or beach communities in relatively arid Southern California feel the sting of rust.

To most vehicle owners, rust is annoying at best, and at worst it's a total automotive meltdown. For those hearty souls in the midst of restoring a classic that's suffering from long years of neglect, the bubble patch on the surface may be the symptom of terminal problems ­­– like the proverbial tip of the boat-sinking iceberg.

The science behind rust

In any discussion of car corrosion, it's important to understand exactly what it is, in scientific terms. The vehicle's steel is a combination of iron, metal impurities and negatively charged free electrons that are attracted to the iron atoms under normal conditions. All that changes when moisture is introduced – moisture in the form of actual water or simple humidity. Through electrolysis, the electrons abandon the iron and head straight for the metal impurities, forming rust.

When you encounter car rust, the conventional approach is to keep poking at it until you hit uncontaminated metal. But in the most serious cases, that just doesn't happen. You scrape and sand and finally see the daylight through the metal. That's when it may be time to call on companies that specialize in providing replacement sheet metal for body panels and floor pans. That's the extreme case. For now, we're going to take a more optimistic approach: car rust can be stopped, despite Neil Young's declaration that "Rust Never Sleeps."

Different types of rust treatment

Sanding rust off the surface of a car

Car rust treatments generally start with elbow grease, removing the bubbles and pock marks with grinders, wire brushes, sandpaper or sand blasting, and taking the infected area down to bare metal. The more deep-seated the rust, the more aggressive the tools. Fortunately, there are some helpful methods that can reduce the amount of physical labor involved when fighting rust.

Working with rust converters

Rust converters represent an excellent do-it-yourself option for rust removal. For modern automotive applications, rust converters come in the form of primers designed for use directly on the rusty surface, with no scraping, grinding, sanding or blasting. In fact, the product has to be applied to rust in order to work. The two components of converters are tannin and an organic polymer. Tannin, a water-soluble natural product derived from a variety of plants, reacts with iron oxide and changes it to iron tannate, a stable blue/black corrosion product. The polymers provide a protective primer layer.

Broad selection of rust converting products

Like anything else, proper application with the best rust converters is key to a rust-free future. While you can toss your grinder and sandpaper, you still have to start with a clean, dust-free surface. A soft wire brush is the best tool to remove any errant particles, followed by a thorough vacuuming of the impacted surface. Soluble salts, like those used to de-ice winter roads, should be rinsed with water, and road grease also needs to be removed.

Converters can be either brushed or sprayed on the surface in an environment where the metal's surface temperature is between 50 and 90 degrees. Check your weather forecast before starting, choosing a day where there's no chance of rain for a full 24 hours after application. Even if the procedure is done in a closed garage, avoid days that threaten any form of moisture.

Once the converter is applied, it takes about 20 minutes for the rust to turn coal black. The reaction is completely cured after 24 hours, but it may take longer if the humidity is higher than 75 to 80 percent.

Rust converters should not be sanded. Instead, the treated surface should be covered with a compatible topcoat. It's vitally important to fully read and understand the manufacturer's directions and recommendations. Like any creeping disease, the best time to deal with rust is immediately. It won't heal itself, and the longer the bubbly patch is allowed to feed on your vehicle, the more radical the procedure that’s required to neutralize it. Catch rust early so your car doesn’t slowly corrode while you're sleeping.

Trying rust paints, acid rust removal and more

Mechanic using tools to restore a metal car panel

There are also rust paints available that seal or encapsulate the rust. These products are highly flammable and include toxic chemicals that require professional application. Acids can also dissolve rust, leaving a thin oxide coating on the surface. Like the paints, acid rust removal necessitates special breathing equipment.

For high-end restorations, metal panels (or the whole car) can be submerged in a hot bath of caustic soda, stripping all the paint down to the metal. The panel is then treated in a tank of alkaline solution and the rust is removed electrolytically. Again, a professional will need to apply these methods, but they’re still great options if you’re short on time or don’t feel confident enough to take on rust removal by yourself.

Understanding the origins of rust treatment

Prior to these modern methods, the first "professional applicators" of the oldest method of rust treatment were probably blacksmiths. To protect their tools, the smithies would coat them with oil and heat them in their forges, not unlike the method of seasoning a cast-iron skillet.

This treatment process creates a hard coating, called magnetite, on the metal surface. The coating is chemically inert and will not react to oxygen or moisture. The path from the blacksmith shop to auto parts counter ran through the mining, construction and agricultural industries as scientists attempted to solve the problem of preserving metals exposed to the elements.

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