CSLB C-33 Painting & DecoratingCoating ApplicationEasy
A painting contractor is applying a stain-blocking primer to a water-damaged ceiling before painting. The primer needs to effectively seal out water stains and prevent bleed-through. Which type of primer is generally considered most effective for this specific application?
- AOil-based alkyd primer
- BClear acrylic sealer
- CWater-based latex primer
- DPVA (Polyvinyl Acetate) primer
Show answer & explanationAnswer & explanation
Correct answer: A. Oil-based alkyd primer
Oil-based (alkyd) primers are highly effective at blocking water stains, smoke stains, and tannins due to their superior sealing properties. While some specific water-based stain-blocking primers exist, a general oil-based primer is usually the go-to for severe stain blocking.
Why the other options are wrong
- B. Clear acrylic sealers are typically for porosity control or dust binding, not for blocking persistent stains.
- C. Standard water-based latex primers are generally poor at blocking severe water stains and may allow bleed-through.
- D. PVA primers are primarily designed for sealing new drywall and are not effective stain blockers.
Stain-Blocking Primer (Oil-Based)
An oil-based (alkyd) primer formulated to seal and prevent the bleed-through of severe stains such as water, smoke, grease, and tannins from wood, providing a clean surface for topcoats.
- Superior sealing properties compared to most water-based primers.
- Effective on a wide range of challenging stains.
- Requires mineral spirits for cleanup and typically has strong odors.
Memory trick: For tough stains, oil-based is the king, preventing any bleed-through sting.