In one sentence, describe what the following article is about:

Sand blasters are powerful pressure washers that project a blend of water and sand to clean a surface. There are different types of sand blasters, so you will make sure that you select one suited to removing graffiti. Beware, sand blasters can remove underlying paint as well, so you will usually only want to use a sandblaster on a plain surface.  Sand blasters can be used to clean a wide variety of surfaces including concrete, metal, brick, masonry, and wood.  Sand blasters can be erosive! Be careful on old stone, brick, and wood, as a sandblaster can speed the deterioration of porous surfaces. Sand blasters can remove paint, rust, and grease as well. For most sand blasters, you'll want to be choosing round silica to clean graffiti from surfaces. It is effective and inexpensive. Of course, make sure that the sand type you choose is suitable for both your blaster and the surface in question. Place your sandblast probe into the sand you will be using and attach the dispensing end to your power washer nozzle. Make sure that your sand source stays dry and moisture free.  Your sand must be completely dry. Moisture could cause the sand to clump which would compromise functionality.  Be sure to use safety goggles! Sand and debris can easily damage your eyes. Before you begin to work on cleaning the graffiti you may wish to familiarize yourself with the sand blaster by doing a trial run on a similar piece of material. Once you are confident that you have the hang of things you'll be able to get started. When you first start, you'll want to sandblast the graffiti at an angle. Firing directly at the graffiti at a 90 degree angle is extremely powerful and can also cause damage to the underlying surface. Begin at an indirect angle and move from there.  You're looking for an angle that removes the graffiti without harming the underlying surface. Once you find that angle, move back and forth methodically. Generally cleaning a square foot at a time is a good way to start. Now that you are set up and know how to use your equipment properly, blast away! Continue to use even, methodical sweeps with the sandblaster and you will have the offending graffiti gone in no time. Once you are done, take a step back and assess your work. Sometimes you'll spot areas where the graffiti is faded but still visible. Get back to work and repeat your prior sandblasting until the surface is clean. Once you are done, carefully pack up your equipment. If you are storing extra sand make sure that it is completely dry and clump-free. You'll also want to inspect the surface for damage. Re-caulk or re-seal any porous corners or seams that may have been compromised by the sandblasting.

Summary:
Select a sand blaster. Choose the right type of sand. Set up your equipment. Carefully test your equipment. Start cleaning the graffiti. Keep going until it is clear. Evaluate your work. Wrap up.