Paint Repair - Topcoating Preparation
1. Topcoating Preparation
Scuffing is done to increase adhesion of the old paint layer to the new topcoat.

When Block Painting or Overall Painting (Overall Recoloring):
Sand the topcoated area using a double action sander with P400 sandpaper.
Manually sand with P600 to P800 sandpaper where the sander cannot access. Be careful not to miss any spots.
Sand only in one direction so that sanding scratches are not as noticeable.
When Gradation Painting:
Scuff off the old paint layer of the primer-surfacer coating area with some extra margin so that scuffed area is a little wider than the gradation border.
For a light solid colored surface, sand with an intermediate compound, or with P1500 wet-or-dry sandpaper.
For a metallic, pearl, or deep solid colored surface, sand with a fine compound or with P1500 wet-or-dry sandpaper.
After scuffing the old paint layer, mask it for topcoating.
1.
Transfer and Cleaning of Vehicle:
Clean any dust and dirt in the paint both first and wet the floor with water. Then transfer the vehicle into the paint booth.
2.
Air Blow Cleaning and Degreasing of Coating Surface:
Degrease and clean the surface, check the masking paper and coating surface for any lifting or peeling. Use a compressed air blow gun to thoroughly remove all dust and dirt from the gaps between parts and panels.
Just before topcoating, wipe the entire coating surface with a tack cloth. Be careful not to apply too much pressure against the surface or the cloth may leave varnish residue on the surface.
NOTE: Do not touch the degreased surface with your bare hands.
3.
Wear safety protection and clean work wear to avoid dust and dirt adhering to the surfaces being painted.
4.
Paint Mixing:
Mixing Hardener and Additive.
NOTE: Follow the manufacturers' instructions for correctly mixing paint.
Mixing Paint:
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Mix the paint, hardener, and paint reducer/thinner to the correct ratio according to the paint manufacturer’s instructions using a microcomputer scale. The amount of hardener must absolutely be correct or it will cause defects after topcoating. The use of a digital measuring instrument is widely used for color mixing.
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It is important to select the appropriate paint reducer/thinner depending upon the ambient conditions.
Example: Use of Paint Reducer/Thinner by Temperature
Type of Paint Thinner
Temperature (reference)
Ultra quick drying type (very cold season)
50 °F (10 °C) or lower
Quick drying type (cold season)
50?59 °F (10?15 °C)
Normal type (warm/cool season)
About 68 °F (20 °C)
Slow drying type (hot season)
77?95 °F (25?35 °C)
Ultra slow drying type (very hot season)
95 °F or higher (35 °C) or higher
5.
Mix the hardener and paint reducer/thinner thoroughly with the paint, filter it with a strainer, and pour it into the spray gun.