Collision Repair Training | United States
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Current Events/News: Advantage Online: 2002 Archives
GM APPLICATION OF ANTI-CORROSION MATERIALS March 25, 2002 -Most vehicle maker recommendations for applying anti-corrosion materials are either vague or nonexistent. In contrast, General Motors released a service bulletin late last year (GM Bulletin No. 01-08-51-003) that lists specific procedures for applying corrosion protection materials to enclosed areas and exterior surfaces. The procedures are to be used during collision repairs on all 2002 and prior passenger cars and light duty trucks. Specific materials and application equipment are included in the bulletin, but a disclaimer leaves the door open for other suppliers: "We believe these sources and their products to be reliable. There may be additional manufacturers of such materials. General Motors does not endorse, indicate any preference for, or assume any responsibility for the products from these firms for or for any such items which may be available from other sources." Accelerated Corrosion Test GM subjected 16 different products to an accelerated corrosion test (GMP9540P corrosion specification). The products were applied, following the product maker instructions, to a total of 135 test panels. A test period of 40, 16-hour days, or 40 cycles, in a salt-spray corrosion chamber was designed to simulate 20 years of on-the-road environmental conditions. From that testing came the specific product recommendations. Enclosed Areas
The application process is similar to most enclosed areas using anti-corrosion material applications. Start by thoroughly mixing the material by shaking the can. Pour as much material as will be used for one application into the applicator gun cup (see Figure 2). Then screw on the spray gun head and set the inlet air pressure. The service bulletin lists some specific guidelines for use:
Access is generally through existing holes at the end (see Figure 3) or in the middle of the part (see Figure 4). After inserting the wand to the end of the rail or panel, trigger the gun and slowly withdraw the wand, about 25 mm (1") per second. See the Video for actual application of the material to an enclosed rail on a 2002 Saturn Vue.
Exterior Areas There are two recommended anti-corrosion materials for exterior use. The aerosol material shown in Figure 5 (Nox Rust X-121B) is specifically for repair areas on full frames, such as welded areas where the original coating has been removed. The original anti-corrosion coating on most frames is a wax. The entire frame is dipped in hot wax, leaving an average 4 mil thick coating that's highly resistant to salt and moisture. Hot wax is favored over electrodeposition coating (E-coat) on frames for several reasons. The E-coat process requires the metal to be extremely clean, and the cleaning process is not easy on a full size frame part. Also, the heated wax flows into the many enclosed areas and corners of a frame easier than E-coat, which only adheres to areas that are electrically charged. Finally, the hot wax process is four times less expensive than the E-coat process.
The product shown in Figure 5 is that same wax material, only with a solvent added to allow it to be applied as an aerosol. The procedure is to apply several light, even coats. The coating looks and performs just like the original coating, because it is.
The other material is for underbody exterior areas. The specific material recommended in the bulletin is a waterborne, rubberized undercoating that's applied with an applicator gun that attaches directly to the container (see Figure 6). It’s not only for use on underbodies, but also door skins, wheel wells, trunks, and floor pan interiors. Conclusion If there was confusion before about the type of anti-corrosion protection to apply during collision repairs, there shouldn't be now, at least on GM vehicles. For enclosed area protection, this involves the use of an applicator gun with high inlet pressure, stiff wand, and a 180° applicator tip.
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