CSLB C-33 Painting & DecoratingSurface PreparationEasy
A painting contractor is preparing an interior wall that has extensive staining from water damage. After cleaning the surface, they notice that some of the stains are still visible. What is the most appropriate next step before applying the finish coat?
- AApply a second coat of the finish paint directly over the stains.
- BApply a stain-blocking primer to encapsulate the remaining stains.
- CWash the wall again with a stronger detergent solution.
- DSand the stained areas aggressively until the discoloration is removed.
Show answer & explanationAnswer & explanation
Correct answer: B. Apply a stain-blocking primer to encapsulate the remaining stains.
Water stains can bleed through standard paint if not properly sealed. A stain-blocking primer creates a barrier that prevents these discolorations from reappearing in the finish coat.
Why the other options are wrong
- A. Applying more finish paint without a primer is unlikely to hide significant stains and risks bleed-through.
- C. Further washing is unlikely to remove stains that persisted after initial cleaning, and the surface needs to be dry before priming.
- D. Aggressive sanding may damage the substrate and is not an effective method for removing deep-seated water stains that have penetrated the surface.
Stain-Blocking Primer
A type of primer formulated to prevent stains (e.g., water, smoke, grease) from bleeding through and discoloring subsequent paint coats.
- Essential for covering tough stains like water, smoke, or tannin.
- Creates a barrier between the stained surface and the new paint.
- Available in oil-based and water-based formulations.
Memory trick: Don't just paint over, block the stain, then make it clean.