Swelling, Sinking

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

CAUSE

Sanding the substrate with too coarse grit sandpaper.

Insufficient dry/cure of undercoats before sanding and topcoating.

Refinishing over soft, soluble substrates (e.g., lacquers, uncured OEM).

Using a poor grade and/or too fast evaporating thinners/reducers for spray conditions causing:

Primer surfacer to "bridge" over sand scratches;

Topcoat to "skin over," trapping solvent which swells sensitive substrates.

Using a solvent cleaner that is too strong for the substrate or using thinner/reducer as a surface cleaner after sanding.

REPAIR

Allow finish to dry/cure, sand smooth, compound or polish to restore gloss.

Or, sand and refinish.

PREVENTION

Sand with recommended grit sandpaper.

Allow undercoats to thoroughly dry/cure before sanding and topcoating.

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.

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.*

Use solvent cleaner designated for either lacquer (soluble) or cured enamel/urethane (insoluble) substrates.

*For best results, use the premium two component undercoat system.