CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting contractor is preparing a newly installed drywall surface for painting. After taping and mudding, which of the following is the most critical step to ensure a smooth, uniform finish and proper paint adhesion?
- AThoroughly clean the entire surface with a damp sponge.
- BApply a PVA (Polyvinyl Acetate) primer-sealer.
- CApply a skim coat of joint compound to the entire wall.
- DSand all joint compounds and patched areas smooth.
Show answer & explanationAnswer & explanation
Correct answer: D. Sand all joint compounds and patched areas smooth.
After taping and mudding, joint compound must be sanded perfectly smooth to eliminate ridges, bumps, and tool marks, which would otherwise be visible through the final paint coats and compromise uniformity.
Why the other options are wrong
- A. Cleaning is necessary after sanding, but sanding is the direct action to smooth the compound.
- B. Priming is important, but not before the surface is smooth; primer won't hide imperfections.
- C. A full skim coat is a repair technique for very damaged walls, not a standard step after standard mudding unless specifically needed.
Drywall Compound Sanding
The process of abrading dried joint compound to achieve a perfectly smooth and seamless surface on drywall before priming and painting.
- Removes ridges, bumps, and tool marks.
- Ensures a uniform texture for paint.
- Typically done with fine-grit sandpaper or sanding screens.
Memory trick: Mud smooth, then prime to seal.