CSLB C-33 Painting & DecoratingSurface PreparationEasy
A painting contractor is preparing a wooden deck for staining. The deck has areas of mildew growth. Which of the following is the most appropriate initial step to address the mildew before staining?
- AApply a coat of oil-based primer directly over the mildew.
- BSanding the mildewed areas with 80-grit sandpaper.
- CScraping off the visible mildew with a wire brush.
- DWashing the deck with a bleach and water solution.
Show answer & explanationAnswer & explanation
Correct answer: D. Washing the deck with a bleach and water solution.
Bleach and water solutions are effective at killing mildew spores and cleaning the surface, which is crucial before applying any finish. Simply scraping or sanding may not kill the spores, allowing mildew to regrow under the new stain. Priming over mildew is ineffective and will lead to premature coating failure.
Why the other options are wrong
- A. Priming over mildew will trap the spores, leading to continued growth and premature coating failure.
- B. Sanding may spread mildew spores and is not effective at killing them; it can also damage the wood grain unnecessarily.
- C. Scraping only removes the visible top layer; it does not kill the mildew spores embedded in the wood.
Mildew Removal from Wood
Mildew on wood surfaces must be killed and cleaned before painting or staining to prevent its regrowth and ensure proper adhesion of the new coating.
- Bleach solutions kill mildew spores.
- Mechanical removal alone is insufficient.
- Proper drying after cleaning is essential.
Memory trick: Mildew Means Must Be Murdered Before More Moisture Makes Mess