(C) Alligatoring

Identification:

Very large checks several inches across, visible to the eye are formed. The large checks resemble the skin of alligators, hence the name "alligatoring".

Description:

This defect is very common amongst coal tar coatings. If a thick coal tar coating is applied, there is a tendency for the outer surface area of the coating to shrink at a faster rate than the body of the coating, resulting in formation of macro checks which cause the coating to become brittle. The macrochecks maintain a minimum thickness so that the damage does not penetrate into the substrate.

Prevention:

• Avoid applying a soft primer under a hardcoat.

• do not apply a coating which has a tendency to oxidize on a soft surface.

• Use reinforcing pigments.

• Monitor the coatings periodically.