Coating corrosion, degradation, and cracking

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Cracking is a form of coating failure that is related to the shrinkage during the aging process of the coating film. When the contraction stress of the film exceeds its cohesion, the difference in expansion promotes the rupture of the coating film. Generally, hard and brittle membranes are more prone to cracking than flexible membranes. An overly thick film will exacerbate cracking. Coating cracking can also be caused by the release of inappropriate solvents from the film. Cracking of the coating can be prevented by using flexible coatings or by adding toughening agents; such coatings should be capable of withstanding the shrinkage stresses acting on the surface under specific operating conditions. In the event of cracks, it is also possible to choose primer, topcoat, or intermediate coat formulations whose expansion and contraction rates are identical. If the cracking failure is not caused by bonding defects, an appropriate coating can be reapplied to bridge the cracks, directly covering the old coating. If the cracking damage is related to poor adhesion, the old coating should be completely removed and repainted.