A water-damaged wall should not be closed up or painted until the source is stopped and the materials have had a chance to dry. Repair scope depends on how long it stayed wet, whether drywall or plaster lost strength, and whether insulation or other materials inside are damp.
Stop the water source before opening or repairing
Identify whether the source is plumbing, roofing, a window, or condensation and shut off water when appropriate. Cosmetic repair while moisture continues will trap the problem behind the new finish.
Decide what can dry and what must be removed
A superficial stain on sound material is different from drywall that is swollen, soft, or crumbling. Wet insulation, damaged gypsum board, and materials contaminated by sewage often require removal rather than surface drying alone.
Dry the cavity before closing the wall again
Use appropriate airflow and dehumidification and confirm that framing and materials have returned to normal moisture conditions. Closing a damp cavity encourages odor, deterioration, and hidden mold.
Repair substrate and finish in that order
Replace damaged material, use appropriate stain-blocking primer where needed, and paint last. If damage is extensive, electrical components became wet, or the water was contaminated, professional assessment is safer than a surface patch.
Sources
- U.S. Environmental Protection Agency — Mold and Moisture — Moisture control, mold prevention, cleanup, and recurrence.