reprinted courtesy of ServiceMagic.com
This information can clarify and help answer some questions about power washing.

Cleaning basics: Knowing the area that needs power washing helps your service professional give you a more accurate estimate. It gives an idea of the kinds of cleaning aids, equipment and time that will be involved.
Surface: The surface material can affect how your service professional will choose to clean the surface. For example, dry ice blasting shoots dense dry ice pellets that turn into a harmless gaseous substance on impact. This option leaves an instantly dry surface which may be ideal if the surface is metal or wood.
Some forms of stucco, like EIFS (Exterior Insulation and Finish System), can be vulnerable to high impact (hail and woodpeckers). Your service professional will need to select a power cleaning option that suits an EIFS stucco surface.
Special options: For specific cleaning and stain removals, certain chemicals or solvents are added to the power washer. For specific or environmentally safe cleaning needs, there are several other blasting methods.
-- Tips courtesy of Service Magic