Pour the course acoustic ceiling texture into a bucket. Add water according to the manufacturer's directions to create a material the consistency of cooked oatmeal. Thoroughly blend the wet texture material using a paint mixer or a stirring stick.
Attach the compression hose to the air compressor. Attach the hopper gun to the end of the compression hose. Use a large spoon to load the texture material into the hopper.
Place a large cardboard box on the floor or other flat surface so its opening is vertical. Plug in and turn on the air compressor. Keeping the hopper upright and the nozzle about 18 inches from the inner wall of the box, spray into the box. Adjust the spraying distance, trigger pressure and aperture size as you practice. Practicing and making minor adjustments will help to achieve a professional-looking textured ceiling.
Lightly spray the ceiling in a 3-foot-square area, beginning on a side or corner of the ceiling. Keep moving to avoid applying too much material in one area. Instruct an assistant to hold the blade of a large putty knife at a shallow angle, almost parallel to the ceiling, and to lightly drag the knife across the wet texture material. Spray an adjacent 3-foot section of the ceiling as your assistant knocks-down the globules with the putty knife. Continue applying and dragging the textural material until the entire ceiling is finished.
Apply a second coat of texturing spray after the first coat has dried to achieve a more dimensional finish; the ceiling will feel cool to the touch until the texturing material has dried. Drag the texturing material with the putty knife after spraying each 3-foot-square section.