CSLB C-33 Painting & DecoratingSurface PreparationMedium
A client requests repainting of a previously painted, high-traffic hallway with oil-based semi-gloss paint. The existing paint is in good condition but very shiny. To ensure proper adhesion of the new water-based latex paint, what is the most critical preparation step?
- AApply a bonding primer specifically designed for glossy surfaces.
- BRoughen the surface with fine-grit sandpaper (e.g., 220-grit).
- CApply a degreaser to remove any surface contaminants.
- DWash the wall thoroughly with soap and water.
Show answer & explanationAnswer & explanation
Correct answer: A. Apply a bonding primer specifically designed for glossy surfaces.
When painting over glossy oil-based paint with water-based latex, mechanical abrasion alone is often insufficient. A bonding primer is crucial to ensure strong adhesion between the dissimilar paint types and the slick surface.
Why the other options are wrong
- B. Sanding helps, but a bonding primer provides superior adhesion, especially when changing paint types.
- C. Degreasing is important for cleaning, but does not address the adhesion issue with glossy surfaces.
- D. Washing cleans the surface but doesn't solve the problem of adhesion to a glossy, oil-based finish.
Bonding Primer
A specialized primer designed to adhere to difficult, slick, or non-porous surfaces, promoting adhesion for subsequent paint layers.
- Essential for glossy surfaces, plastics, ceramics, and metals.
- Creates a strong mechanical and chemical bond.
- Often used when switching paint types (e.g., oil to latex).
Memory trick: For a slick surface, bond it tight, then the new paint will hold just right.