Socrates said, “The secret of change is to focus all of your energy, not on fighting the old, but on building the new." Change is inevitable in our industry. Enamel gave way to lacquer, which gave way to multiple versions of urethane-based paints and now of course waterborne paints. Resistance is not the answer to the destiny you must endure; embrace it and learn to move forward.
Aluminum vehicles have been around for decades with exotic and race vehicles and also in production vehicles. Since 1995, aluminum has been used by many European OEMs to construct their vehicles either with closure panels, hybrid construction or intensively. Now the US market is finally starting to catch on and the masses are realizing there is going to be change. Aluminum repair is only difficult, or in some cases, impossible, because it is different from repairs performed on steel and plastics. For some reason, no one in the industry argues that a steel part can be repaired like a plastic or composite component, or vice versa. Therefore, why it is it that all these so-called experts try to say aluminum can be repaired like steel, when obviously it cannot? There are similar procedures, but very different techniques; this is why aluminum repair will be extremely difficult, if not impossible, for most. This brings us to the topic of this article — refinishing differences for aluminum components. Please keep in mind that this article is directed at damage assessors or estimators and not refinish technicians, as they will get training from their specific paint manufacturer.
Procedures for new replacement aluminum components and repaired components does differ slightly because of the need to prevent cross contamination, which could cause contact corrosion and eventually lead to galvanic corrosion, which in some cases could be catastrophic. You will always need to follow what your paint manufacturer states in their manual on product use and preparation procedures; but in some cases, you may need to refer to the OEM repair manual, as they may have specific refinish procedures for their vehicles. Here is a general example from multiple paint manufacturers on aluminum refinishing procedures.
Aluminum refinishing procedures
**Note – It is required that separate tools and sandpaper are used on aluminum components to avoid cross contamination and potential galvanic corrosion issues.
Clean the repair area prior to any sanding or grinding. Use the recommended product to remove wax, grease and other contaminants. Soak a cloth with cleaner and wipe the area thoroughly. Use a clean, dry cloth to dry the area. Do not allow cleaner to dry on surface prior to wiping with dry cloth.
**Note: We used a steel vehicle in the photos below as an example, but this is the same procedure that would be performed on a aluminum vehicle. This BMW is red and the inner panels will be refinished in red and clear coated after installation.
General repair requiring body filler procedures
Remove paint using a DA sander with 80 grit to bare metal. Vacuum dust and clean area with a dry cloth. Featheredge the area stepping from 80 to 180 grit DA paper.
Re-wipe the area with the recommended cleaner. Apply with a soaked cloth and dry with a clean, dry cloth. Do not allow cleaner to dry on surface prior to wiping with dry cloth.
Most recommend an epoxy primer-sealer, and generally require a medium wet coat over the bare metal area. Bake the primer-sealer at 140°F metal temperature for 20 minutes using IR or conventional booth or allow to air dry for 16 hours and allow to cool. Once again, this is just a general explanation, please check with you paint manufacturer for specific procedures.
Apply body filler over primed area to fill the imperfection. After body filler has hardened, sand with 80 grit followed by 100, 120, 150 and 180 grits until damaged area is leveled.
When body filler process is finished, featheredge the repaired area working from 80, 100, 120, 150, 180, 220 to 240 grit DA sandpaper to ensure a proper featheredge.
Prime bare metal areas with an epoxy primer-sealer. Apply one medium wet coat and allow to flash 30-45 minutes prior to applying primer-filler.
Apply a urethane primer-filler per label directions. Allow primer to dry and sand as necessary.
Proceed with balance of refinishing process.
BMW rear body panel, E-Coat primed grey
General repair without body filler procedures
Featheredge repair area stepping down from 80, 100, 120, 150, 180, 220, 240 to 320 grit DA sandpaper, dependent on the depth of repair. Use finest grit possible. Vacuum dust and wipe with a clean cloth. If bare aluminum is present, a pre-treatment type primer is generally required. Wipe the area with the required cleaner. Apply with a soaked cloth and dry with a clean, dry cloth. Do not allow cleaner to dry on surface prior to wiping with dry cloth.
Most paint manufacturers require a self-etching primer and to apply one medium coat over the bare metal area and allow to flash dull. After the self etch has flashed 30 minutes, apply a urethane-fill primer.
A urethane primer-filler is generally applied using an outside-in technique. Allow each coat to flash before applying the next coat. Allow primer to dry thoroughly and sand as necessary and then proceed with balance of refinishing process.
Additional Procedures
Like with steel panels, time must be added for the masking and application of chip guard. Many times you will have to check with the OEM repair information on where chip guard is applied. Most applications are smooth and you either need the OEM location of applications, or you will need to measure the film thickness. Generally the database providers allow for 0.5 hrs refinish for the first panel and 0.3 hrs refinish for each additional panel, and texture matching set up is not included. Typically, chip guard is found on the leading edge of the hood panel, around the windshield posts, leading edge of the roof panel and to the lower areas of the fenders, doors, rocker panels and quarter panel dog-leg areas.
Many OEMs and paint manufacturers require full backside refinishing to help protect the backsides from debris buildup that can cause contact corrosion and eventually lead to galvanic corrosion and panel failure, such as refinishing and clear coating the backside of fenders and door assemblies. Additionally, much like steel quarter panels, the backsides of aluminum quarter panels must be refinished. Backside refinishing is not included in any of the three major database providers and must be manually added to the estimate. Time must be added for the preparation and application of primers, base coats and clear coats.
Another important procedure that is not included is the feather edge, prime, and block sand (FPB) procedure. This must be calculated by the damage assessor and is based on a percentage of the repair time to the component. Contrary to some articles we have read, some paint manufacturers do require self-etch primer on aluminum components. Some OEMs require epoxy primer be applied to the panel prior to applications of body filler. Additionally, there are some paint manufacturers that may require higher grades of sandpaper grit to finish off the bare aluminum to prevent sand scratches. It is imperative that the refinish technician reads the paint manufacturer and OEM repair protocols prior to any applications of material. There are many articles on calculations for the FPB process. Both Mike Anderson, another ABRN contributor, and myself have written articles on the process and calculations.
Lastly, although not common with OEM steel components, many new OEM aluminum components come with either a shipping primer or no primer at all. You will need to refer to the OEM repair procedures and/or paint manufacturers’ procedures for the preparation to refinish those types of components.
One important thing to remember is that aluminum repair is somewhat similar to steel repair, but there are some very different procedures, equipment and techniques. Please feel free to contact me if you have any questions.
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