PCS Coating Failure Analysis and Remediation 2 — Questions and Answers
Question 1: Which type of coating failure is characterized by fine, shallow cracks that do not penetrate through the entire coating film thickness?
- Checking (Correct answer)
- Crazing
- Splitting
- Delamination
Correct answer: Checking
Checking refers to fine, shallow cracks confined to the upper layers of the coating film that do not penetrate through to the substrate.
Question 2: Rust staining on a coating surface in the absence of visible coating failure most likely indicates which underlying condition?
- Cathodic disbondment
- Mill scale or embedded iron remaining on the substrate (Correct answer)
- Contamination introduced in the coating material
- Moisture vapor transmission through the film
Correct answer: Mill scale or embedded iron remaining on the substrate
Residual mill scale or iron particles embedded in the surface during improper preparation will corrode under or through the coating, causing rust staining without obvious delamination.
Question 3: When investigating a coating failure, what must be the first step before any remediation work begins?
- Remove all failed coating immediately
- Apply new coating over the failed area
- Document and photograph the failure in detail (Correct answer)
- Test the dry film thickness of the failed coating
Correct answer: Document and photograph the failure in detail
Thorough documentation and photography before any remediation preserves evidence needed to diagnose the root cause and prevent recurrence.
Question 4: Cathodic disbondment of a protective coating is most commonly associated with which system?
- Solvent-based alkyd coatings
- Cathodic protection systems (Correct answer)
- Excessively thick epoxy coatings
- High-temperature silicone coatings
Correct answer: Cathodic protection systems
Cathodic protection systems generate hydroxyl ions at cathodic sites beneath the coating, raising pH and breaking down adhesion, causing cathodic disbondment.
Question 5: When a coating failure extends through the entire coating system down to bare substrate, which remediation approach is required?
- Spot repair with a compatible topcoat only
- Power tool cleaning and spot prime only
- Complete removal to bare substrate and full recoating (Correct answer)
- Overcoating with a penetrating sealer
Correct answer: Complete removal to bare substrate and full recoating
When failure extends to the substrate, complete removal to bare metal and full system recoating is required to ensure a sound, adherent new system.
Question 6: Osmotic blistering beneath a coating is primarily caused by which condition?
- Excessive dry film thickness applied in one coat
- Water-soluble salts trapped beneath the coating film (Correct answer)
- UV exposure degrading the coating binder
- Application at ambient temperatures above 90°F
Correct answer: Water-soluble salts trapped beneath the coating film
Water-soluble salts (such as chlorides or sulfates) beneath the coating create osmotic pressure by drawing moisture through the film, forming blisters.
Question 7: Which test is most appropriate for determining whether an existing coating is compatible with a proposed overcoat system?
- Cross-cut adhesion test
- Solvent rub test (Correct answer)
- Holiday detection test
- Wet film thickness measurement
Correct answer: Solvent rub test
The solvent rub test (MEK rub test, ASTM D5402) helps identify the coating type and degree of cure, which determines compatibility with proposed overcoats.
PCS Coating Failure Analysis and Remediation 2
Which type of coating failure is characterized by fine, shallow cracks that do not penetrate through the entire coating film thickness?