(D) Cracking

Identification:

Macroscopic cracks are formed all along the coating applied on metallic or wooden substrate. 

Description:

The following are the major reasons for developing of the cracks.

• Aging of the coating

• Weathering of the coating

• Developing of stresses in the coating between the film and the substrate which exceeds the strength of the coating

• Use of excessive coating thickness when using waterborne epoxy coatings on inorganic Zinc coatings

• The expansion and contraction of the surface in harsh environment leading to the development of stresses.

• Wetting and drying cycles and adsorption and desorption of humidity. These cycles also contribute to stresses and de-adhesion of the coating

• The application of a hard drying coating over the surface of an underlying soft coating

Prevention:

• Apply thin coatings

• Use film reinforcing pigments of fibrous type to relieve stresses

• Use addivites to soften the coating

• Mechanically remove all paint and re-coat