Empty the room of furnishings, then cover the floor with a drop cloth to protect from falling ceiling texture. Line the walls with plastic sheeting, covering them completely. Secure the sheets to the walls with masking tape.
Clean the ceiling with a pH-neutral cleanser. Mix the cleanser with water in a large bucket, according to manufacturer's instructions. Dip a mop into the bucket and squeeze the mop head to remove excess liquid. Use the mop to remove any dirt or debris from the ceiling. Rinse the mop in a second bucket containing only clean hot water. Don't saturate the ceiling with liquid. Rinse the ceiling with clean water and allow the ceiling to dry completely.
Spray a primer coat of interior paint onto the ceiling with a paint sprayer to create a surface to which the texture can adhere. Allow the coat to dry for two hours, then place a topcoat in the final color you wish. Allow this coat to dry for two hours before texturing.
Add water to the texture compound until it's the consistency of thick pancake batter. Add compound pigment to the material to match the primer, if a colored primer is used. Pour the compound into an acoustical spray gun. Spray the texture onto the ceiling, covering the ceiling with an even layer of the texture. Wait 20 minutes after application for the texture to begin to set while remaining tacky.
Knock down the sprayed texture with a knock-down knife held at a 30-degree angle to the ceiling. Chop off the tips of the sprayed texture to leave the bases intact, rising slightly from the ceiling surface. Wait 24 hours for the texture to dry.