CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing an interior wall that has extensive grease and nicotine stains. After initial cleaning, residual discoloration remains. What is the most effective type of primer to prevent these heavy stains from bleeding through the new topcoat?
- APVA (polyvinyl acetate) primer
- BWater-based latex primer
- COil-based stain-blocking primer
- DShellac-based primer
Show answer & explanationAnswer & explanation
Correct answer: D. Shellac-based primer
For severe stains like heavy grease and nicotine, shellac-based primers are superior due to their exceptional sealing properties and quick drying time. While oil-based primers are good, shellac offers the strongest barrier against the toughest bleed-through.
Why the other options are wrong
- A. PVA primers are primarily for sealing new, porous drywall and have poor stain-blocking capabilities.
- B. Water-based latex primers are generally not strong enough to block heavy grease and nicotine stains.
- C. Oil-based stain-blocking primers are effective for many stains, but shellac-based primers offer even better sealing for severe cases.
Shellac-Based Primer
A highly effective primer derived from natural shellac resin, known for its exceptional stain-blocking, odor-sealing, and adhesion properties.
- Best for severe water, smoke, nicotine, and grease stains.
- Excellent for sealing odors (smoke, pet).
- Dries very quickly and adheres well to many surfaces.
Memory trick: When stains are tough and odors linger, shellac is the primer, the stain-finger.