Paint - Tri-Coat Repair: Overview
88cad09Bulletin No. T-88-168
File in Group 10
Number 136
Corp. Ref. No. 811703
Date Aug. '88
SUBJECT: TRI-COAT PAINT REPAIR
MODELS AFFECTED: 1987-1989 ALLANTES 1988-1989 SEVILLE TOURING SEDANS 1989 SEVILLE 1989 ELDORADOS
The Allante, Seville, and Eldorado are currently available in WHITE PEARL TRI-COAT COLORS which are unique from other Cadillac colors. Unlike the current basecoat/clearcoat finishes, these colors are applied in a three-stage process, therefore, the repair will require additional attention.
Although these colors may appear to be identical, they are two different colors. The Allante uses code 55 White Metallic WA# 9069, where the Seville and Eldorado use code 93 White Diamond WA# 8933. These colors also use different base coat whites. The Seville and Eldorado use code 40 White WA# 8554, without the clear coat as the base coat white, while the Allante uses a base coat white unique to the WA# 9096.
NOTE: A Tri-Coat Paint Repair training program, course number 22001.41, is available through General Motors Product Service Training.
FIGURE 1 - BASECOAT/CLEARCOAT:
The Ultimate Basecoat/Clearcoat Color Shade (Figure 1):
Light that penetrates the surface of the cured paint film, reflects off the aluminum flakes, then passes around the pigment of varying densities which will produce the ultimate color shade.
FIGURE 2 - TRI-COAT:
The Ultimate Pearl Luster Effect (Figure 2):
Light striking the applied film of titanium dioxide on the flakes of mica creates the pearl luster effect by allowing the light to deflect at different angles. The light deflection determines the ultimate pearl luster effect you see.
The repair of these white pearl colors will require different techniques and a different application process. Many of the conventional application techniques used on non-clearcoat and basecoat/clearcoat metallic colors do not apply when repairing a tri-coat finish.
Non-clearcoat or basecoat/clearcoat metallic colors can be adjusted by the following variables:
1. Reduction (amount and choice of solvent)
2. Air pressure
3. Gun distance
4. Fluid adjustment
5. Fluid tip size
The color is affected as follows:
^ Higher air pressure/increased reduction will cause a metallic color to shift to the light side on the face and dark on the flop.
^ Lower air pressure/decreased reduction will cause a metallic color to shift to the dark side and go light on the flop.
Theoretically, when a metallic paint film is applied wet as it would be at lower air pressure and lower reduction, the aluminum flake will settle deeper in the paint film and be surrounded by the color pigment causing a darker appearance. The color will react in the opposite when the variables are reversed.
This theory does not apply to the white pearl tri-coat system. The white basecoat is a solid material, therefore, will not be sensitive to the same variables that affect metallic colors. On the other hand, the pearl coat (or mid-coat) is very sensitive to film build. With tri-coat pearl colors, film build is the primary means of a color match, NOT gun technique. For this reason a let-down panel should be used to determine the number of pearl coats required to match the OEM finish. This tool should be made prior to starting a repair. The let-down panel will be used to match paint on the repair vehicle and should be retained for future repairs.
NOTE: Separate let-down panels will have to be made for the STS Seville and the Allante because of the different colors involved.
FIGURE 3 - LET-DOWN PANEL:
"The Let-Down Panel":
The let-down panel should be used as an aid to determine the approximate number of pearl coats (mid-coats) that will be necessary to achieve a proper color match. This is done by comparing the various pearl coat film build areas on the let-down panel to a panel adjacent to the repair area prior to starting the repair. It can be made in the following manner, refer to Figure 3:
1. Apply the white base to hiding.
2. Mask the panel in five sections leaving the first section exposed.
3. Apply a single medium wet coat of the pearl material.
4. Remove the masking paper from the second section.
5. Apply a medium wet coat over the entire uncovered area of the panel.
6. Repeat the above steps until the five sections are completed, leaving only one coat on the last section.
NOTE: The let-down panel should illustrate five different film builds of pearl coat.
7. Once the panel is dry, mask off one half of the panel dividing it lengthwise. Apply two coats of clear on the unmasked half of the panel. Remove the masking paper and let the panel dry.