During coating inspection, most people focus on thickness, gloss, or adhesion. Few realize that a small factor – porosity in coatings – determines the coating’s lifetime. Tiny voids can act as channels for moisture, chemicals, or metal ions to penetrate. This weakens the film from within. When left uncontrolled, porosity becomes the reason coatings lose protection even if they look flawless outside.
WHAT IS POROSITY IN COATINGS
Definition of porosity
Porosity is the volume fraction of air or microscopic voids inside the coating structure after curing. These pores may appear as capillary tunnels or closed bubbles. They are invisible to the naked eye but strongly affect moisture resistance, insulation, and chemical durability.
Causes of porosity formation
Several factors create porosity in coatings. When solvents evaporate too fast, the surface cures before bubbles escape, forming micro-voids. Inconsistent pigment or filler sizes create gaps between particles. Incomplete crosslinking or wrong mixing speed can trap gases inside. Application conditions such as humidity, temperature, or spray pressure can also increase porosity.
IMPACT OF POROSITY ON COATING QUALITY
Effect on corrosion resistance
Pores act as “pathways” for water, oxygen, and salt ions to reach the metal surface. Corrosion then starts beneath the coating, causing blistering or rust from inside. For protective coatings on tanks, pipelines, or outdoor steel, even small porosity levels can lead to early coating failure.
Effect on adhesion and mechanical strength
When coatings contain many pores, layer bonding becomes weak. The film may peel, crack, or delaminate under stress. Vibrations, impacts, or thermal expansion reduce flexibility. In PU or epoxy systems, high porosity can break the polymer network, lowering overall strength.
Effect on appearance and coverage
Porosity affects not only performance but also visual quality. Trapped bubbles cause pinholes, dull spots, or uneven gloss. High porosity reduces surface smoothness and reflectivity. For high-finish products like automotive parts, electronics, or home appliances, such defects are unacceptable.
METHODS TO MEASURE AND EVALUATE POROSITY
Electrochemical test
This method measures insulation performance of coatings. An electrode touches the coating surface to detect leakage current. If porosity exists, current passes through. It reveals weak points in the film. This technique suits corrosion-resistant coatings.
Microscopy and image analysis
Optical microscopes or SEM devices observe pore density and size directly. Cross-section images provide quantitative data. Users can compare different samples or aging stages. Despite longer testing time, this method gives the highest accuracy.
SOLUTIONS TO CONTROL AND REDUCE POROSITY
Optimize formulation and solvent ratio
Solvent evaporation rate affects film formation. If too fast, the surface seals early and traps gas. Choosing proper solvents and adjusting viscosity and pigment/binder ratio helps reduce porosity in coatings.
Use defoamers and dispersing agents
Defoamers break bubbles during mixing or spraying. Good dispersants keep pigments uniform and prevent voids. Together, these additives create dense and smooth coatings with lower porosity.
Use high-quality resins and hardeners
Base materials define polymer structure after curing. Systems like Desmophen or Bayhydur from Covestro and Uralac from Allnex form dense networks. They reduce micro-voids while maintaining gloss and durability.
VICHEM – OFFICIAL DISTRIBUTOR OF CHEMICAL ADDITIVES FROM COVESTRO, SINOPEC, BUHLER, AND MORE
Vichem is the official distributor of additives and chemical materials from brands such as Covestro, Sinopec, and Buhler in Vietnam. We supply high-quality products and global-standard after-sales service.
- Technical consulting: Support customers in selecting suitable materials.
- Color testing: Vichem experts run matching tests to meet design standards.
- Application support: Assist customers during production integration for optimal results.
For more information, please contact:
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