Apply the chemicals to your surface and treat your stains before washing. When you turn the pressure washer on, keep the pressure washer away from any surface (and innocent bystanders). Pressure from the water stream can hurl you up in the air and throw you flat on your back for all neighbors to see. Water pressure can be powerful.
Once the stains are treated, use your pressure washer to clean, scrub and rinse. How hard you scrub will depend on the pressure given to the water, the amount of water that's flowing out, and the angle of the flow.
Pressure washer tips are color-coded. For those manufacturers who subscribe to universal coloring standards, the black tip is for chemical and soaping applications. The red tip can be dangerous. Red indicates a zero degree angle, and the pressure and power it exerts can seriously damage many surface materials. The zero degree angle is created for “blasting” embedded soils away in tough surfaces, such as concrete. A yellow 15 degree tip is powerful enough to remove a lot of dirt and grime, and the green 25 degree angle tips are fine for a lighter washing. There's also specialty tips and tips that spray water and spin water. Find the right tip for your job.
The powerfulness of the washing will depend on the PSI (pounds per square inch, just like the tires on your car), and the Gallons per Minute (GPM) (the flow of water through your showerhead). The higher both numbers are, the more forceful the spray. 1400 PSI and 2 GPM is fine for small, easy jobs such as power washing a home deck or residential garage floor. A pressure washer with 2500 PSI and 3 GPM is often efficient for power washing the outside of a house. If you're targeting peeling paint, you want at least 2000 PSI. Although, it is possible that power washing will not get every last bit of paint off the surface - but it will save you hours of scraping and scrubbing. Just scrape off the last bits of paint, and give it a final wash and rinse.
Pressure washers can make you feel powerful, but they can be dangerous to people and materials. It takes some skill and common sense to operate a pressure washer, but power washing is often the best solution to making sure your surface area is prepared for painting. By power washing a surface, you'll get a powerful paint finish, and you can make powerful use of the time you saved by taking on another painting project.