PCS Coating Failure Analysis and Remediation 3

Question 1

White powdery deposits on the surface of a zinc-rich primer before topcoat application most likely indicate what condition?

Accepted Answer

Zinc corrosion salts (white rust) from normal weathering

Answer

White powdery deposits on zinc-rich primers are zinc corrosion salts (white rust) that form during normal atmospheric exposure and must be removed before topcoat application.

Question 2

Mudcracking (also called mud cracking) in a coating film is most often caused by which application error?

Accepted Answer

Applying an excessively thick wet film in a single coat

Answer

Applying too thick a wet film causes the outer surface to skin over while the interior is still wet; as the interior shrinks during drying, it cracks the surface in a mud-crack pattern.

Question 3

Which instrument can detect corrosion beneath an intact coating without removing the coating?

Accepted Answer

Ultrasonic thickness gauge

Answer

An ultrasonic thickness gauge can measure remaining substrate thickness through intact coatings, revealing metal loss caused by corrosion occurring beneath the film.

Question 4

What does the pull-off adhesion test (ASTM D4541) specifically measure in a coating failure investigation?

Accepted Answer

Tensile strength of adhesion between coating and substrate

Answer

ASTM D4541 measures the tensile stress required to pull a coating free from the substrate, quantifying the adhesive bond strength in pounds per square inch (psi) or MPa.

Question 5

Sagging or runs in a freshly applied coating film are most commonly attributed to which cause?

Accepted Answer

Over-thinning of the coating or applying an excessive wet film thickness

Answer

Over-thinning reduces viscosity too much, and excessive wet film thickness adds too much material, both of which cause the coating to flow downward under gravity before it can cure.

PCS - Protective Coatings Specialist Certification Practice Test

PCS - Protective Coatings Specialist Certification Practice Test

PCS Coating Failure Analysis and Remediation 3