Finish Analysis and Correction For the New Car Prep Technician
FIGURE 1 - THE SURFACE:
When we refer to the "surface", we're talking about the entire finish
- topcoats and undercoats - everything short of the bare body metal (Figure 1).
The immediate problem involved with breaking through the surface is that when the surface is broken (by sanding or by some other means) the bare metal is exposed to air and moisture - and the possibility of future corrosion.
A second reason to avoid breaking through the surface is that there is always the possibility of a color mismatch in areas that are repainted.
Factory Painting Materials and Methods
There are two assembly line painting methods used, each with its own set of properties. One method uses thermo-flow acrylic lacquer finishes, while the other uses thermo-set enamel finishes.
FIGURE 2 - ACRYLIC LACQUER CURING PROCESS:
Acrylic Lacquer
A thermo-flow acrylic lacquer finish is applied and reflowed in ovens at temperatures of approximately 325 degrees Fahrenheit, so the paint surface flows together. The paint cures by solvent evaporation and the result is a level, glossy coat that requires little or no compounding (Figure 2). Because of the heat involved, the acrylic lacquer cannot be reflowed after any plastic, rubber or glass is mounted on the car.
FIGURE 3 - ACRYLIC ENAMEL CURING PROCESS:
Acrylic Enamel
Heat is also used to cure thermo-set acrylic enamel finishes. However, unlike acrylic lacquers which only undergo a process of solvent evaporation when curing, enamels undergo an additional process of absorption of oxygen from the air (Figure 3). Enamel provides a durable, lustrous finish that cannot be reflowed once it is cured.
When you're called upon to correct a paint imperfection, don't break the surface unless it's absolutely necessary!
Simple Finish Repairs
Depending on the nature of the imperfection, you may be able to correct it using measures that won't disturb the color coat or undercoat. When possible, attempt to rub out and polish the imperfection. If necessary, wet sand the imperfection with ultra-fine or equivalent sandpaper, then rub out and polish the area. To correct dirt in paint conditions use a dirt-nib file to remove dirt speck (nibs) without disturbing surrounding surface. But whatever the case, always use the simplest possible method to repair an imperfection.
Identifying Acrylic Enamel Finishes
Because of the different paint properties discussed in Section 1, there are slightly different steps to be followed when repairing over acrylic enamel finishes.
FIGURE 4 - BODY IDENTIFICATION PLATE:
Before you begin making repairs, you must determine whether the factory finish is acrylic lacquer or acrylic enamel. To do this, check the body identification plate or the service parts label on the vehicle (Figure 4).
For identification of acrylic lacquer paint, the letter "L" or the word "Lacquer" will be used. For the acrylic enamels, the letter "W" or the word "Water" will designate water-borne acrylic enamel. Also, the letter "E" or the word "Enamel" can be used to designate the paint type as acrylic enamel, solvent reduced.
DIRT-NIB FABRICATION:
Fabrication of Dirt-Nib File
1. Break vixen file into 1-1/2 inch long lengths. See Figure 5.
2. Dress of sharp ends off.
3. Place 400 to 500 grit sandpaper on flat surface and draw file in fore-aft motions until file teeth are smooth (a light machine oil hastens the operation). Check file on a painted surface. It should remove the nib and leave no scratches.