PCS Coating Failure Analysis and Remediation 1 — Questions and Answers
Question 1: What is the most common root cause of coating delamination from a steel substrate?
- Excessive dry film thickness
- Inadequate surface preparation (Correct answer)
- High ambient humidity during application
- Insufficient mixing of coating components
Correct answer: Inadequate surface preparation
Inadequate surface preparation is the leading cause of coating failures because contaminants and poor anchor profile prevent proper adhesion.
Question 2: Which type of coating failure is characterized by dome-shaped hollow projections rising from the coating surface?
- Chalking
- Cratering
- Blistering (Correct answer)
- Alligatoring
Correct answer: Blistering
Blistering appears as dome-shaped hollow projections caused by moisture, soluble salts, or osmotic pressure beneath the coating film.
Question 3: Which coating defect results from UV degradation of the organic binder, leaving loose pigment particles on the surface?
- Checking
- Chalking (Correct answer)
- Sagging
- Pinholing
Correct answer: Chalking
Chalking is caused by UV degradation of the binder, which releases pigment particles that remain loosely on the surface and can be wiped away.
Question 4: Which condition most commonly causes pinholes (holidays) to form in an applied coating?
- Over-application of coating
- Low substrate temperature
- Solvent entrapment during curing (Correct answer)
- Excessive dry film thickness
Correct answer: Solvent entrapment during curing
Solvent entrapment during curing creates small voids or pinholes as trapped solvents escape through the drying film, leaving holiday defects.
Question 5: What is the term for a coating failure in which paint separates from the substrate or underlying coat in large continuous sheets?
- Flaking
- Erosion
- Delamination (Correct answer)
- Spalling
Correct answer: Delamination
Delamination refers to the separation of a coating film in large sheets from the substrate or between coats, often exposing bare metal.
Question 6: Which standardized test method is used to evaluate coating adhesion by making a crosshatch cut and applying tape per ASTM D3359?
- Dry film thickness measurement
- Cross-cut adhesion test (Correct answer)
- Holiday detection test
- Pull-off adhesion test
Correct answer: Cross-cut adhesion test
ASTM D3359 cross-cut adhesion test involves scribing a grid pattern through the film, applying tape, and rating how much coating is removed to assess adhesion.
Question 7: Alligatoring (crocodile cracking) of a coating surface is typically caused by which condition?
- Application of a hard topcoat over a soft, incompletely cured primer (Correct answer)
- Excessive surface profile roughness
- Application in cold weather below 50°F
- Insufficient pigment-to-binder ratio
Correct answer: Application of a hard topcoat over a soft, incompletely cured primer
Alligatoring occurs when a rigid topcoat is applied over a softer, incompletely cured undercoat that continues to move, causing the hard film to crack in a pattern resembling alligator skin.
PCS Coating Failure Analysis and Remediation 1
What is the most common root cause of coating delamination from a steel substrate?