CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing a large exterior concrete wall that has significant chalking. The wall will be painted with an acrylic latex paint. Which of the following is the most effective approach to prepare this surface?
- AWire brush the entire wall, then apply a latex conditioner.
- BThoroughly pressure wash the surface to remove all loose chalk, then allow to dry.
- CApply an oil-based primer directly over the chalking to seal it in.
- DScrape off the chalking with a putty knife, then apply a masonry sealer.
Show answer & explanationAnswer & explanation
Correct answer: B. Thoroughly pressure wash the surface to remove all loose chalk, then allow to dry.
Chalking is the degradation of the previous paint film into a fine, powdery residue. It must be thoroughly removed, typically by pressure washing or vigorous scrubbing, to ensure proper adhesion of new paint.
Why the other options are wrong
- A. Wire brushing is labor-intensive for large areas and may not remove all chalk; a latex conditioner is not a substitute for thorough cleaning.
- C. Priming over significant chalking will not provide a sound surface; the primer will adhere to the chalk, which will then detach.
- D. Scraping is ineffective against chalking, which is a powdery residue, not a thick layer; a masonry sealer is for sealing, not cleaning.
Chalking Removal
The process of eliminating powdery residue (chalk) from weathered painted surfaces to ensure proper adhesion of new coatings.
- Caused by paint degradation.
- Must be completely removed.
- Commonly done by pressure washing or scrubbing.
Memory trick: Wash the chalk, then prime it right.