C33 Paint and Coating Types 5 — Questions and Answers
Question 1: Which coating is most appropriate for painting a galvanized metal roof that has been weathered for two years?
- Vinyl acrylic latex
- Direct-to-metal (DTM) acrylic or a galvanized metal primer (Correct answer)
- Interior alkyd enamel
- Flat latex ceiling paint
Correct answer: Direct-to-metal (DTM) acrylic or a galvanized metal primer
Weathered galvanized metal should be coated with a DTM acrylic or a primer specifically formulated for galvanized surfaces to ensure adhesion without saponification.
Question 2: A 'two-component' (2K) polyurethane topcoat differs from a single-component product mainly because:
- It is applied with a brush only
- It requires mixing a base and an isocyanate hardener before use and provides a chemically crosslinked film (Correct answer)
- It dries through solvent evaporation alone
- It cannot be tinted
Correct answer: It requires mixing a base and an isocyanate hardener before use and provides a chemically crosslinked film
Two-component polyurethanes mix a polyol base with an isocyanate hardener that crosslink into an extremely hard, chemical-resistant film far superior to single-component versions.
Question 3: When a specification calls for a 'vapor barrier' coating on interior concrete walls, the contractor should select:
- Flat latex paint
- High-build epoxy or bituminous coating with very low moisture vapor transmission (Correct answer)
- Alkyd semi-gloss enamel
- Shellac-based primer
Correct answer: High-build epoxy or bituminous coating with very low moisture vapor transmission
Vapor barrier coatings like high-build epoxies or bituminous products have extremely low moisture vapor transmission rates (MVTR) sufficient to retard moisture migration through concrete.
Question 4: Zinc-rich primers are used primarily on structural steel because zinc:
- Acts as a sacrificial anode, corroding preferentially to protect the steel substrate (Correct answer)
- Reflects heat and UV radiation
- Increases the flexibility of the coating film
- Accelerates the drying of topcoats
Correct answer: Acts as a sacrificial anode, corroding preferentially to protect the steel substrate
Zinc is anodic to steel; when exposed, it corrodes first, providing galvanic (cathodic) protection to the underlying steel and preventing rust.
Question 5: A contractor must coat a surface immersed in water. Which generic coating type is most appropriate?
- Flat latex
- Coal tar epoxy or underwater epoxy (Correct answer)
- Interior alkyd
- Shellac
Correct answer: Coal tar epoxy or underwater epoxy
Coal tar epoxies and underwater-grade epoxies are specifically formulated for continuous immersion service, providing excellent water and chemical resistance.
Question 6: What distinguishes a 'self-priming' topcoat from a standard topcoat?
- It contains higher pigment loads that eliminate the need for a separate primer coat on properly prepared surfaces (Correct answer)
- It dries faster than conventional paints
- It can be applied without mixing
- It is solvent-free
Correct answer: It contains higher pigment loads that eliminate the need for a separate primer coat on properly prepared surfaces
Self-priming topcoats have higher solids and adhesion-promoting resins formulated to penetrate and bond to bare substrates, eliminating a separate prime coat on suitable surfaces.
Question 7: Which VOC category typically applies to flat interior architectural coatings under California Air Resources Board (CARB) and South Coast AQMD regulations?
- 100 g/L limit
- 50 g/L limit (Correct answer)
- 250 g/L limit
- No VOC limit applies to interior coatings
Correct answer: 50 g/L limit
CARB and SCAQMD regulations set a 50 g/L VOC limit for flat interior coatings (as of current rules), one of the strictest limits for this category in California.
C33 Paint and Coating Types 5
Which coating is most appropriate for painting a galvanized metal roof that has been weathered for two years?