Coating Strength

Definition - What does Coating Strength mean?

Coating strength refers to the ability of a coating to stick to a surface or substrate. Coating strength allows the engineer to estimate the life of a structure and durability of a coat, and similarly, occurrence of corrosion.

Factors affecting coating strength:

  • Chemistry and physics of surface
  • Chemistry and physics of coating materials
  • Stresses in coating or substrate
  • Application and service environment

Corrosionpedia explains Coating Strength

Coating strength is the measure of adhesion of paint or coating to a surface or substrate. A coated surface is viewed as a three-component system consisting of:

  • Paint
  • Substrate
  • Paint/substrate interface
Coating is useless unless it has good adhesion. While the coating remains on the substrate, it can protect against:
  • Weather
  • Chemicals
  • Scratches
  • Impact
  • Stress

The durability and performance of coatings depend on two basic properties: cohesion and adhesion. Cohesion is the inner strength of a material, and it is determined by the strength of molecular forces in the bulk. Adhesion is the strength of the bonds forming between one material and another. The adhesion of a coating is improved by surface roughness. Failures related to adhesion determine the life of the coating.

In the paint and coating industries, paint adhesion testing is often used to determine if the paint or coating will adhere properly to the substrates to which they are applied. There are three different tests to measure the resistance of paints and coatings from substrates:

  • Cross-cut testing measures the resistance of paints and coatings to separate from substrates by utilizing a tool to cut a right-angle lattice pattern into the coating, penetrating all the way to the substrate.
  • Scrape adhesion testing measures the tenacity of the adhesion of organic coatings when applied to smooth, flat panel surfaces.
  • Pull-off adhesion testing is a measure of the resistance of a coating to separation from a substrate when a perpendicular tensile force is applied.
Where coating strength is low, coating failure is likely. Causes of coating failure include:
  • Overheating
  • Blistering
  • Cracking
  • Hardening
  • Softening
  • Peeling
  • Staining
  • Burning
  • Undercutting

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