The automotive-paint industry is an ever-changing world. When the first cars rolled off the assembly line, they were painted with a brush. The first Corvettes, meanwhile, were finished with lacquer paint. This paint was easy to spray and match, and the results were stunning. Unfortunately, lacquers were also highly toxic, a trait that led the EPA to ban their use in most applications.
Today, many collision shops are transitioning from solvent-based to waterborne basecoat systems in anticipation of new air-quality regulations scheduled to go into effect in January 2009. Manufacturers are also expected to develop automotive coatings that meet California's strict regulations for VOC (volatile organic compound) emissions.
Although we had hoped to use a waterborne system for this phase of our project, none were available in our area at the time of the repair. Accordingly, we resorted to a traditional solvent-based finish to make our color dreams a reality.
When it comes to applying paint, remember this simple, three-word mantra: Practice, practice, practice. It's one thing to read about painting a car, quite another to successfully perform the job. Hone your technique by spraying every junk panel you can find. Eventually you'll build up the confidence to move on to the real thing.
3M Product List
* Trizact Hookit Clearcoat Sanding Disc - P1500 (PN 02088) or Trizact Hookit II Clearcoat Sanding Disc - P1500 (PN 02069)
* Trizact Hookit Foam Disc - P3000 (PN 02085) or Trizact Hookit II Foam Disc - P3000 (PN 02075)
* Perfect-It Rubbing Compound (PN 06085/06086)
* Perfect-It Machine Polish (PN 06064/06065)
* Perfect-It Ultrafine Machine Polish (PN 06068/06069)
The next stage of preparation begins with wet-sanding by hand using 600- or 800-grit sandpaper. Alternatively, you may use a dual-action sander with a 3M interface pad and a 1,000-grit sanding disk. It is strongly recommended that you sand the entire panel so that the application of paint and clearcoat forms a seamless repair.
Tape and paper off any areas where you don't want overspray. Be sure to "back tape"-that is, apply the tape to the masking paper and then fold it back so that half of the sticky side is on the car and the other half is folded back and facing up. Once this is done, use plastic sheeting to cover any areas that remain exposed.
The final step before painting is to wipe the area with a tack cloth and use unoiled compressed air to remove any particles that may have settled on the car.
Apply a coat of Polyolefin Adhesion Promoter and allow five minutes to dry. The adhesion promoter will help the paint stick to the surface.
On the first application of basecoat, spray only enough product to just overlap the repaired area (#1 in photo). Continue to spray single coats until opacity (dullness) is achieved. Extend each coat slightly beyond the previous one (#2 in photo), allowing the basecoat to flash between coats. You can accelerate the flash time by blowing air at a 45-degree angle on the spot repair with your spray gun. You may tack off between coats only if there are foreign objects in the basecoat that will not blow out. Most paints can be reduced by as much as 50 percent on the last coat. This will help make the color more transparent, facilitating a more uniform blend (#3 in photo). Be sure to check with your paint manufacturer for the proper procedure.
To help illustrate the technique used, we painted the repaired area with white basecoat. Normally the basecoat color would be applied at this stage.
Our paint technician applies the first application of basecoat. Notice that he is spraying only enough product to just overlap the repaired area.
We decided to paint our bumper off of the car to ensure that there were no unpainted edges.
When replacing or repairing a panel that is adjacent to another panel, blend the basecoat into both sections to achieve a seamless match. Spray the first application of basecoat approximately three inches onto the car body wherever it meets the panel. Extend the next coat slightly beyond the previous one, allowing the basecoat to flash between coats. Again, you should be able to reduce the paint by as much as 50 percent to help make the color more transparent and form a more uniform blend.
Two to three coats of clearcoat should be sprayed onto the entire panel wherever the basecoat was applied. This should make the transition between the original finish and the spot repair invisible.
After drying, carefully remove the plastic sheeting, paper, and tape.
If you need to remove nibs or sags, you can wet-sand the finished product with very fine high-grit sandpaper. A 1,500-grit sandpaper is a good choice for hand- or pad-sanding. You can also use a dual-action sander with a 3M interface pad and a 1,500 clearcoat sanding disk.
To refine sanding scratches even further and cut buffing time in half, switch to 3,000-grit on your interface pad. Use discretion and move slowly. If you start seeing color, you've gone too far. Some imperfections may be too deep to remove with this process. When sanding, remember to match the finish on the rest of the car.
Buffing and reassembly are the final steps in the paint repair. To remove sand scratches from wet-sanding, we used the 3M Perfect-It Paint Finishing System. The first step is to use a wool pad with a buffing compound at a buffer speed of 1,200-2,000 rpm. To eliminate the swirl marks left from the compound, use the black foam compounding pad with a machine polish. It's best to work a single 2x2-foot area at a time. Lastly, to remove the remaining swirl marks, change to the blue foam compounding pad with an ultrafine machine polish. In this step, a light pressure should be used. Do not buff dry; leave a wet film on the surface while using the buffer.