Patterned cracking results when the top coat is not bonding properly with the base coat. Alligatoring occurs most frequently with multiple applications of solvent-based paint (oil or alkyd)–in fact, such cracking may simply be a sign of aging, as time and prolonged exposure to the elements ultimately sap solvent-based coatings of their elasticity and turn them brittle.

Causes:

• A solvent-based top coat, which dries hard, was applied over a more flexible latex primer or base coat.
• The top coat was applied before the undercoat was fully dry.
• The top coat dried too fast and shrank as a result of exposure to direct sunlight.

What to do:

• Completely remove the failed paint down to bare wood and sand the surface. Feather-sand any remaining paint so there is a smooth transition to the bare wood, and remove the dust with a tack cloth. Use an exterior latex primer and repaint with exterior latex paint.