CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing an interior plaster wall that has several small, non-moving hairline cracks. What is the most appropriate repair material for these cracks before priming?
- AElastomeric caulk
- BFiberglass mesh tape embedded in joint compound
- CSetting-type joint compound (hot mud)
- DAcrylic latex caulk with silicone
Show answer & explanationAnswer & explanation
Correct answer: C. Setting-type joint compound (hot mud)
For non-moving hairline cracks in plaster, a setting-type joint compound (hot mud) is generally preferred. It dries hard, resists shrinking, and bonds well to plaster, providing a durable repair that can be sanded smooth. Elastomeric or acrylic caulks are more for flexible joints or dissimilar materials.
Why the other options are wrong
- A. Elastomeric caulk is designed for flexible, moving joints and not ideal for rigid, non-moving plaster cracks that need to be sanded smooth.
- B. Fiberglass mesh tape is typically for larger drywall seams or cracks, not hairline plaster cracks.
- D. Acrylic latex caulk, even with silicone, is too flexible and not designed for rigid plaster repairs that require sanding and a hard finish.
Plaster Hairline Crack Repair
The process of filling small, non-moving cracks in plaster walls or ceilings to achieve a smooth, paintable surface.
- Setting-type compounds are preferred for rigidity.
- Cracks must be clean and free of loose debris.
- Surface must be primed after repair.
Memory trick: Plaster cracks need a 'setting' solution, not a 'flexing' one.