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If you were asked for a short description for anti-corrosion compound, the material that is sprayed onto the backside of panels and inside rails after repairs, it is likely that "thin film" and "fine mist" would not be included in the wording. However, that is exactly the description given to a new type of anti-corrosion compound now available that uses what is collectively called thin-film technology.
Thin-film technology products are polymer resin-based, anything more descriptive than that is proprietary. They're a completely aerosol system being distributed by at least two product makers, Bonding Solutions with their Like90 Corrosion Protection System, and Sherwin Williams with their Shield Corrosion Protection System (see Figure 1). The two systems actually come from the same source that has its origins in the aerospace industry. The same material that's being recommended for spraying inside rails and panel cavities has been used for years on aluminum welds and sealing joints on aircraft. Besides an anti-corrosion compound, the line also includes a weld-through primer, also polymer resin-based, and a solvent-based cleaner.
Thin-Film Anti-Corrosion Compound
Figure 2 - The dedicated spray wand for the anti-corrosion compound is stiff, but flexible to allow a 360° spray pattern to reach all areas of a cavity.Most anti-corrosion compounds are wax-based, and even though applied as a fog spray, can quickly build up a heavy coating with the consistency of honey. The thin-film technology products start out thin, and the resulting coating is thin. This allows the material to not only coat the interior surfaces, but also wick out between the welded flanges from the inside. There is a dedicated wand that fits onto the aerosol spray can nozzle with a 360° fan pattern tip on the other end (see Figure 2). Like other anti-corrosion compound systems, the wand is for inserting into existing holes or into rails to apply the material onto areas that cannot be easily reached.
The thin-film nature of the material, combined with its creeping capability, allows applying it to joint edges after welding. On panel applications where there are no cavities, such as a welded radiator core support, the same cavity compound can be applied to the outside of the joints (see Figure 3). Just like it does from the inside, the thin film penetrates between the flanges from the outside, wicking around the welds to replace the weld-through primer that burned away. Excess material is cleaned off with the solvent-based remover, since it is not a good base for painting.
Figure 3 - On welded joints, the anti-corrosion compound can be sprayed on the outside of the joint after welding to allow it to wick into the joint.
There are two anti-corrosion compounds in each system. With the Shield system, there is a clear and a black compound, both identical except for the color. With the Like90 system, there's a dry film compound for sealing the joints after welding. The compound for cavity protection is a wet film that's self healing, similar to conventional anti-corrosion compounds.
Product specialists say it's perfectly OK to apply more coats of the cavity compound inside cavities, and even apply another brand of conventional wax-based anti-corrosion compound over the thin-film technology product, but it's not necessary.
Weldable Weld-Through Primer
The thin-film technology weld-through primer differs from other weld-through primers available in that it is not zinc- or copper-based, so it's not conductive. This allows the thin-film technology weld-through primer to be welded through. Our experience showed no problems with porosity when welding GMA plug welds without cleaning the material.
The instructions say to apply a very light coating on both mating surfaces and wait ten minutes before welding. The primer is still tacky at that point. Any weld-through primer on surfaces that will be refinished is cleaned off with the solvent remover.
Future Collision Repair Applications
Thin-film technology is also being considered for spraybooth masking and liquid masking applications. Liquid masking was actually the first collision repair application for the technology some years ago. The new plans are to improve that product. The product makers are also showcasing the benefits of thin-film technology to vehicle makers, though there are no specific recommendations or endorsements as of yet.
Conclusion
Thin-film technology products are one of the new offerings for automotive corrosion protection. The polymer resin-based aerosols are being offered as a thin anti-corrosion compound and weld-through primer with some unique qualities.
This article first appeared in the April 28, 2011 edition of the I-CAR Advantage Online.
