CSLB C-33 Painting & DecoratingSurface PreparationMedium
A painting crew is preparing an interior wall that has significant areas of efflorescence due to past moisture intrusion. After addressing the moisture source, which of the following is the most effective method to clean the efflorescence from the substrate before priming?
- ABrush off the loose salts and then wash the surface with a dilute acid solution.
- BApply a strong alkaline cleaner and rinse thoroughly.
- CScrape off the powdery deposits and then wipe with a damp cloth.
- DSand the affected areas with 80-grit sandpaper until the efflorescence is no longer visible.
Show answer & explanationAnswer & explanation
Correct answer: A. Brush off the loose salts and then wash the surface with a dilute acid solution.
Efflorescence is crystalline salt, which is best removed by brushing to get rid of loose material, followed by an acid wash (like vinegar or muriatic acid) to dissolve remaining salts, then thorough rinsing.
Why the other options are wrong
- B. Alkaline cleaners are not effective against efflorescence, which is typically calcium carbonate or sulfate.
- C. Wiping with a damp cloth can redissolve and redistribute the salts, potentially leading to recurrence.
- D. Sanding can be ineffective against deeply embedded salts and creates hazardous dust; it's not the primary method for efflorescence removal.
Efflorescence Removal
The process of cleaning powdery white salt deposits (efflorescence) from masonry surfaces after the moisture source has been mitigated.
- Caused by soluble salts migrating to the surface and crystallizing.
- Requires addressing moisture source first.
- Typically removed with brushing and dilute acid wash.
Memory trick: Stop the water, scrub the salt, then acid it all.