CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing to repaint a previously painted, high-gloss enamel door frame. The existing finish is in good condition with no peeling or chipping, but the new paint will be a latex semi-gloss. Which of the following surface preparation steps is essential to ensure proper adhesion of the new paint?
- AThoroughly sand the entire surface with fine-grit sandpaper (e.g., 180-220 grit).
- BPressure wash the door frame and allow it to dry completely.
- CClean the surface with a degreaser, then apply a liquid deglosser.
- DApply a bonding primer directly over the high-gloss enamel.
Show answer & explanationAnswer & explanation
Correct answer: A. Thoroughly sand the entire surface with fine-grit sandpaper (e.g., 180-220 grit).
High-gloss surfaces are too smooth for new paint to adhere mechanically. Sanding with fine-grit sandpaper creates a 'tooth' or microscopic profile, allowing the new paint to grip the surface effectively.
Why the other options are wrong
- B. Pressure washing is for exterior cleaning; it will not dull a high-gloss enamel surface or create a profile for adhesion.
- C. Deglossers can help, but mechanical sanding is generally more reliable and effective for creating a proper profile.
- D. While a bonding primer helps, sanding is still crucial for optimal adhesion over high-gloss surfaces.
Dulling Glossy Surfaces
The process of physically abrading a smooth, glossy surface to create a microscopic profile (tooth) for improved adhesion of new paint.
- Essential for painting over high-gloss enamels.
- Achieved primarily through sanding.
- Enhances mechanical adhesion of subsequent coatings.
Memory trick: Glossy slides, sand to 'bite'.