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Rust Never Sleeps

Neutralizing metal corrosion

It 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.

The Creep

No one is truly safe from 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.

No More Metal

The conventional approach to rust is to keep poking at it until you hit uncontaminated metal. 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's time to turn to companies like Year One that specialize in providing replacement sheetmetal for body panels and floor pans. That's the extreme case, and we'll deal with installing panel replacements in a following article. For now, we're going to take a more optimistic approach: rust can be stopped, despite Neil Young's baleful song that "Rust Never Sleeps."

In any discussion of 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.

Treatments

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.

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 removed electrolytically.

Prior to these 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 process creates a hard coating, called magnetite, on the metal surface. This 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.

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 changing it to iron tannate, a stable blue/black corrosion product. The polymers provide the protective primer layer.

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 needs to be removed as well.

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, longer if the humidity is higher than 75 to 80 percent.

Rust converters should not be sanded, but should be followed by 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 required to neutralize it. So catch it early so it can't neutralize your vehicle while you're sleeping.