CSLB C-33 Painting & DecoratingSurface PreparationHard
A painting contractor is preparing an exterior PVC trim board for painting. The trim is new, clean, and has a smooth, glossy finish. To ensure proper adhesion of the new paint, what surface preparation step is most critical?
- AWashing with a strong alkaline cleaner.
- BLightly scuff sanding the entire surface.
- CApplying a solvent-based adhesion promoter.
- DApplying a direct-to-plastic primer without sanding.
Show answer & explanationAnswer & explanation
Correct answer: B. Lightly scuff sanding the entire surface.
New PVC trim often has a smooth, glossy surface that paint struggles to adhere to. Lightly scuff sanding creates a mechanical 'tooth' for the paint to grip, which is critical for long-term adhesion. While some DTM primers claim to adhere without sanding, scuff sanding is still the most reliable and critical step for smooth, glossy plastics like PVC.
Why the other options are wrong
- A. Washing removes contaminants but does not create the necessary surface profile for adhesion on glossy PVC.
- C. Adhesion promoters can help but are usually supplementary to mechanical abrasion on glossy surfaces.
- D. Relying solely on a DTM primer without mechanical abrasion is less reliable for optimal adhesion on very smooth PVC.
PVC Surface Preparation
The process of preparing smooth, glossy PVC (polyvinyl chloride) surfaces to ensure proper paint adhesion.
- Scuff sanding is critical for mechanical adhesion.
- Cleanliness is also essential.
- Use primers designed for plastics for best results.
Memory trick: Glossy PVC needs a 'scuff' to make the paint tough.