Should you undercoat or rust proof your vehicle?

It’s back. Let’s just call it rust. Beginning in the 1980’s Auto Manufacturers launched a focused effort to reduce the warranty costs of corrosion and to build a marketing story around those efforts. Using improved processes, technologies and components they made great advances. The use of zinc coated steels and electrostatic primers and the expanded use of seam sealers greatly reduced corrosion concerns. We also saw an evolution of the metals used, from mild steel to high strength steel, ultra high strength and now boron steel. This evolution in materials has continued and is forecast to continue in future generations of new vehicles.

undercoatThese improvements emboldened vehicle manufacturers to extend their anti corrosion warranties from one year to three, five and even ten years against corrosion due to a defect in materials or manufacture. Perversely, successes brought about by these changes have led to the reemergence of the old auto nemesis, rust. Advertising has indoctrinated us with the belief that modern vehicles don’t rust so fewer vehicles are being protected in the aftermarket. Couple that with the fact that owners are now keeping their vehicles longer than ever before and the introduction of new snow and ice control chemicals, and you have a misinformed public operating in a corrosion risk rich environment.

Road salt? Old news. Liquid calcium chloride and magnesium chloride are now the de-icing chemicals of choice. They are more effective but far, far more corrosive. In fact, the federal Highway Administration estimates that corrosion now costs the nation’s transportation industry and it’s infrastructure $30 Billion per year! Many states are even using magnesium chloride for dust control on unpaved roads, so just because it might not snow where you live doesn’t mean your customer’s vehicles aren’t exposed to rust causing chemicals. Corrosion protection is important regardless of geography!

During the manufacturing / assembly process, vehicle manufacturers use specialized processes to install corrosion barrier products on the vehicle frame and body panels. Metal fatigue, paint refinishing, welding, and time can cause these barriers to break down. So, now this vehicle is in your shop for repairs, how are you going to protect the repairs against failure due to corrosion?

While you can’t duplicate the manufacturer’s processes in your shop, you can install corrosion protection, in fact, it would be irresponsible to not do so!

Many paint and primer type applications promise to provide a corrosion barrier and do, to a point. However, they lack the flexibility to move when the body or frame flexes and can’t stop all moisture from reaching the metal. This is why hem flanges and overlap flanges will often exhibit corrosion in as little as a year following a repair. Cavity Wax and Undercoating products provide an inexpensive and effective corrosion barrier. Simple to install, these products can protect your repair and your reputation.

Ford Motor Company and Chrysler LLC recognized this fact, and in 2007, introduced their own brands of Cavity Wax and non-rubberized Undercoating, (Motorcraft and Mopar respectively) and now specify their use in both sheet metal and structural repairs. These were products that withstood rigorous engineering review. You should consider only those products that have been tested to ASTM B-117 or SAE-J2334 when choosing corrosion barrier replacement material. All brands of cavity wax and undercoating type products are not created equally. In addition to Ford and Chrysler, other vehicle manufacturers are preparing to alter their collision repair procedures to include a stronger focus on rust protection. Some insurers, as well, are paying closer attention during inspections to the corrosion protection that they are being billed for.

Now, let’s sort out some misunderstanding about terms. The term “Under Coat” has been incorrectly used as a blanket term to refer to corrosion barrier coatings. In fact, we have a couple of options: Under Coat and Cavity Wax or Rust Inhibitor. There are two areas that are typically treated, exposed areas and those areas that are enclosed or cavities. Under Coat is used in areas that are easily accessible and exposed directly to the road; in other words, the underbody and wheel wells of the vehicle. Under Coat not only protects against corrosion, it also has a sound deadening and cosmetic function. It must be able to withstand abrasion and impact from road debris. The material that is used in the vehicle cavities needs different characteristics than Under Coat. Since the cavities are enclosed, abrasion is not an issue, but enclosed cavities tend to hold moisture. A quality cavity wax will displace moisture and seek unprotected metal. Because we are often treating seams, crevice penetration or “creep” is a key feature for cavity protection fluids. Since we often can’t see the surfaces we’re treating in a cavity, a product that is spray atomized is preferable to ensure a quality application.

This requires specialized equipment that the supplier of the Cavity Wax should also have available for you. This equipment may cost under $100.00 to over $500.00. It is important to use the equipment recommended by the manufacturer of the cavity wax. Typically, the product is matched to the equipment to ensure proper application and good economy of use. Air pressure requirements specified in the product usage directions are often specific to the recommended equipment and should be followed. Most quality application equipment will offer a selection of application wands, sometimes called lances. A fan spray wand producing a 360 degree pattern is useful in frame sections. A direct spray pattern wand is helpful when treating flanges and seams. Finally, a rigid wand can be useful in some applications. These types of tools make it possible to treat doors, rocker panels, fenders, hoods, trunks, hatches and quarter panels on a fully assembled vehicle. All paint work should be completed before application of the cavity wax as the final corrosion barrier.

When it comes to installing undercoating, the areas to be treated are typically in plain sight. As a result the equipment used to install undercoating is somewhat less sophisticated and also less expensive. Siphon or “Schutz” style guns are available from many sources at many prices. Bear in mind though that the air pressure recommended by the undercoat’s manufacturer is a recommendation for their specified equipment. Undercoating should not be used as a substitute for cavity wax! When spraying undercoat, take care to stay at least 6 inches away from any exhaust components, transmissions and other areas that generate a lot of heat. Disc brakes components, other than brake lines, should also be avoided.

Rubberized undercoating products have been with us for years but have some weaknesses when it comes to corrosion protection. Often when the coating is cut by road debris water will work its way under the coating forming a “pocket.” This water may contain some of the corrosive chemicals we discussed earlier thus forming a corrosion cell against the underbody of the vehicle. Rubberized coatings typically require greater surface preparation than do asphalt based coatings and may not adhere to PVC and other factory installed underbody coatings.

Undercoating is in evolution due to increased costs of components. Asphalt and solvent prices have increased wildly over the past two years. Water based coatings are widely available and many coating manufacturers are experimenting with different solvents and different bases. For now though, nothing has been shown to perform better than an asphalt / wax solvent dispersed coating. No major vehicle manufacturer of which we are aware has tested and approved the “experimental” products. The water based products are intriguing and certainly remove any compliance concerns. However, dry time is typically much longer, shelf life is shorter and freezing is a problem. As the cost issue continues to drive innovation in the chemistry expect to see some varieties of coatings that will address these issues as well as performance concerns.

A careful application of cavity wax or undercoating will leave little overspray; however, there will be some clean up of the vehicle and of the equipment. Inexpensive Mineral Spirits is the clean up solvent of choice. It can be poured into the pressure pot of the cavity wax gun and sprayed through the gun and wands for a quick and effective clean up. You can attach your undercoating gun to a used bottle containing some Mineral Spirits and spray it clean very quickly.

So, rust is back with a vengeance. You know it, the vehicle manufacturers know it, and the insurers know it. You can protect your repairs and your reputation by making sure to follow the vehicle manufacturer’s recommendations when it comes to replacement of the factory installed corrosion barriers. It’s the right thing to do!

Brandon Lee is a freelance writer and blogger. He enjoys traveling, cooking, and working on automobiles in his spare time. 

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