Airbrushing involves using an air-operated gun to apply paint to a variety of surfaces, ranging from T-shirts to automobiles. A skilled airbrush artist can turn just about any surface into a work of art. Murals are paintings typically done on a large surface, such as a wall or a house--indoor or outdoor. Murals are often done in public places where they will be on display a good deal of the time. Painting a mural with an airbrush isn't difficult, but can be time consuming. With a little patience and the right tools, even one with little art experience can do it.
Clean the surface you plan to airbrush on. Ensure the surface is relatively smooth. Water is sufficient to take away normal dirt and grime. You may need a pressure washer only if the surface is extremely dirty and you can't clean it by hand or with a regular water hose. Let the surface dry thoroughly before you begin working.
Use a slide projector to project a smaller guide image onto the wall. You can use stencils and do the mural by hand if you have basic drawing talent, but projecting the image allows even a beginner to airbrush a mural. Many skilled artists use this method as well. Paint either just the outlines needed to get the basic image on the wall or use the projected image as a guide through the entire process. Use a 0.4mm needle to airbrush the image outline onto the wall.
Paint the colors onto your mural using a 0.4mm nozzle. Step back frequently to take in the scope of your work. Don't worry about adding the shading for depth until you've painted your entire mural. Trying to do it while you're doing the coloring will force you to switch between black and color too often.
Paint your shadings with black when you feel all of your colors are evenly applied. Use a 0.4mm needle to add lines for shadow. This is the stage where you want to thicken any hard lines necessary to give the elements of your mural more definition as well. Here, you are essentially finishing your wall mural.
Finish your mural with two or three coats of non removable varnish and two coats of a removable varnish. The non removable will act as a barrier between your work and the removable varnish, which can be taken off later on when your mural needs to be cleaned or freshened up. This is especially important for outdoor murals.
If you have the tools, consider having two or three airbrush guns set up during the coloring phases, especially if you will be mixing colors frequently.