Frequently referred to as galvanic corrosion, rust costs American businesses an estimated $276 billion annually to repair the damage it causes. Of that, $50 billion is spent by the transportation industry on vehicle repair/replacement and infrastructure.*
“It’s all about economics,” says Scott Colvin, PPG brand manager, commercial transport. “A working truck generates revenue and profits. A truck sidelined for rust repairs produces nothing.
Once rust starts, it can’t be completely eliminated without replacing the parts it’s affected. The trick is to prevent it in the first place.”
Rust occurs when dissimilar metals are in contact with each other and exposed to an electrolyte. Here’s how rust comes about:
1. Using dissimilar metals. . .
Every metal has corrosion potential, or anodic index rating. The further apart the two different metals are indexed, the faster the rate of rust.
2. That are in contact . . .
The two metals must be touching for corrosion to occur. With trucks, its hinges, steps, doorframes, mounting brackets and fasteners often have different metals in contact.
3. And exposed to an electrolyte.
The electrolyte (water or road salt) serves as an electrically conductive material that transfers corrosion from the more resistant metal to the weaker one. The most destructive electrolytes are road deicers because they’re excellent conductors and readily attack truck undercarriages and bodies.
Modern manufacturing all but dictates the use of different metals; however, conditions that promote corrosion can still be reduced. A liquid or solid barrier, e.g., polyethylene tape, synthetic fasteners, nylon washers and other inserts, can eliminate or insulate metal-to-metal contact. The barrier also prevents electrolytes from reaching metals and slows corrosion.
The corrosion process develops slowly, sometimes unseen and unnoticed until it’s too late. According to Colvin, prevention is critical. Corrosion damage can’t be reversed; you need to stop it before it starts.
Rust protection begins with the selection of primers and topcoats used in truck assembly.
“Truck protection should begin with the build,” Colvin explains. “Top quality paints provide the fundamentals of corrosion resistance. Advanced coatings can also help prepare a truck for the working world. Most quality-focused truck body builders apply a heavy-duty protective coat during the assembly process. That primary layer provides a cost-effective barrier between substrate metals and electrolytes and against road debris, abrasives, chemicals and other types of abuse.”
When ordering a truck body, a variety of primer options is available; the chemistry of each affects its anticorrosion strength. Zinc-rich epoxies offer premium protection as part of a three-coat system that includes epoxy or urethane primers and topcoats. Epoxy primers present adhesion and corrosion properties that frequently make them the leading option for the mid-coat application in a three-coat system. Polyurethane primers are used in some applications for fast cure speed and smooth appearance. Climate, humidity, rain, snow and expected service life can influence primer choice. Coatings manufacturers, including PPG, recommend selecting primers on the basis of performance expectations (versus cost), since performance is critical to longevity.
While topcoats are generally linked to color, gloss and vibrancy, they play an essential role in corrosion protection by guarding primers from deterioration. They serve as the first line of corrosion defense by slowing down the impact of water and road salts.
“Technologies are always advancing,” adds Colvin. “At PPG, we have new DTM (direct to metal) topcoats that provide protection with just one layer and robust universal primers that are appropriate for multiple substrates — steel, aluminum, stainless steel.”
Colvin notes that some of today’s post-assembly premium coatings are based on advanced aliphatic polyurea technology that provides an increased level of protection over previous formulas. Coatings of this type offer ideal protection for a truck’s exterior high-use work areas such as running boards, steps, truck beds and storage cabinets. “Aliphatic polyurea is the best in polyurea coatings,” he explains. “The coating is sprayed on and gives a truck body and chassis exceptional resistance to corrosive elements. There are several products on the market using this technology. The PPG product, DURABULL® Extreme Duty Protective Coating, is a particularly robust application. The coating is also extremely color stable and displays excellent UV weathering characteristics.”
An aliphatic polyurea layer dries in minutes after application, provides superhard impact and crack resistance and can last up to 10 years. It can also be tinted to match a company’s color scheme. Mainly applied at the assembly stage, aliphatic polyurea coatings can also be sprayed onto vehicles already in use.
ECK® compound, a corrosion resistant coating from Van Nay LLC is another effective option. This compound is intended for use in a broad range of body-building and manufacturing applications in which dissimilar metals may come in contact with each other. ECK is based on electrolysis corrosion control, serving as a barrier against galvanic corrosion. It resists all types of corrosion, including those resulting from magnesium-chloride and calcium-chloride salt residue on roadways. These compounds are generally safe for painted and unpainted surfaces, can withstand temperatures to 1,000 degrees Fahrenheit and suitable for use on rubber and plastic. The coating replaces anti-seize, dielectric-grease and Mylar tape products. Petroleum-based, it contains no silicone and won’t dry or wash off. When protected from rust, bolts and fasteners function properly.
Protection doesn’t stop with the body. Shielding the undercarriage is a lso critical. For that, a heavy-duty, water-based layer, such as PPG’s CORASHIELD® anti-chip coating or other similar product, can be highly effective. The product can be sprayed, rolled or brushed under wheel wells and on adjacent areas during assembly or after a truck has been in service. A heavy coating guards against the constant threat of damage that road debris poses, weakened parts and deterioration.
Blistering paint, rough spots, cracking or lifting and peeling of a truck’s finish may indicate corrosion. Colvin recommends a comprehensive approach that covers almost the entire vehicle with a variety of coatings. “PPG’s commercial coatings, for example, fight corrosion on all surfaces,” he says. “Since individual trucks and fleets have different requirements, the best way to determine what you need is to ask your coating representative for a corrosion audit. The audit will help you find your most cost-effective solution.”
Colvin offers one other important piece of advice: Wash your truck—frequently. The best protective measures can be compromised if a truck isn’t washed regularly. Washing often, including spraying the undercarriage, helps remove salt and dirt, and reduces the chances of corrosion.
“We understand that truck owners want greater durability and productivity from their trucks.” summarizes Colvin. “The cost of protective coatings depends on the products, but that cost is always going to be less expensive than a replacement truck or major repairs. Don’t think of protective coatings as an expense; they’re an important investment in your business.”
*Source: Federal Highway Administration [FHWA-RD-01-156].