7. Coating Failures

7.4 Types of Failures

(D) Cracking


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




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



  • 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