A water damaged ceiling needs immediate attention to prevent structural weakening and mold growth.
Step 1: Stop the Source
Find and stop the source of water before touching the ceiling.
Step 2: Assess the Damage
Prod the damaged area with a screwdriver. If soft or crumbling it must be cut out. If stained but solid it can be treated and repainted.
Step 3: Dry Completely
Use a fan heater or dehumidifier. Allow several days for serious water ingress.
Step 4: Cut Out Damaged Sections
Cut back to the nearest joists. Install new plasterboard and screw to the joists. Apply jointing tape over joints and cover with joint compound.
Step 5: Treat Stains
Apply stain blocking primer to all water-damaged areas before repainting. Water stains bleed through normal paint no matter how many coats you apply.