Sand scratches

Visible lines or marks in the paint film that follow the direction of the sanding process.

Cause:

1. Sanding the substrate with too coarse grit sandpaper.
   
2. Insufficient dry/cure of undercoats before sanding and topcoating.
   
3. Refinishing over soft, soluble substrates (e.g., lacquers, uncured OEM).
   
4. Using a poor grade and/or too fast evaporating thinners/reducers for spray conditions causing:
   A. Primer surfacer to 'bridge' over sand scratches.
   B. Topcoat to 'skin over,' trapping solvent which swells sensitive substrates.
   
5. Using a solvent cleaner that is too strong for the substrate or using thinner/reducer as a surface cleaner after sanding.

Repair:

1. Allow finish to dry/cure, sand smooth, compound or polish to restore gloss.
2. Or sand and refinish.

Prevention:

1. Sand with recommended grit sandpaper.
   
2. Allow undercoats to thoroughly dry/cure before sanding and topcoating.
   
3. Rub a small area of the old finish with a shop towel saturated with lacquer thinner. If the old finish is soluble or undercured, apply appropriate sealer.
   
4. Select recommended thinner/reducer based on temperature, humidity, air movement, and size of repair. Avoid 'bridging' existing scratches by applying primer surfacer in thin wet coats, allowing adequate flash time between each coat.
   
5. Use solvent cleaner designated for either lacquer (soluble) or cured enamel/urethane (insoluble) substrates.