Remove furniture from the room and place drop cloths along the floor to protect your finishes.
Pour half of the compound into a clean five-gallon bucket.
Add enough tap water to the compound to achieve a consistency like that of pancake batter.
Connect the spray gun to the hopper and compressor tank with an air hose.
Pour the compound into the hopper and set the compressor to 25 psi.
Stand back from the wall approximately two feet, and spray the compound onto the wall. Work from the top of the wall to the bottom, then shift over and work back upwards. Use this manner to cover the entire wall.
Allow the peaks of the dollops of compound on the drywall to lose their shine. This takes roughly 15 minutes after application.
Use the knockdown blade to gently flatten the peaks of the compound. Work from top to bottom and keep the blade nearly parallel to the wall to easily "knock down" the compound. It takes approximately 24 hours for the compound to fully dry.