Washing your windows with a pressure washer is fast, and the wand allows you to reach second-story windows without having to climb all the way to the roof edge. Counterbalancing these advantages -- and possibly outweighing them -- are the dangers of cracking glass or loosening window putty with the high pressure water and the fact that pressure washing often doesn't do that good a job. If pressure washing is for you, be safe; use low pressure and a wide spray pattern.
Pros Don't Do It
Contractors that specialize in pressure washing siding and include window cleaning as part of their services usually advertise hand-cleaning for the windows. The best way to clean a window is to use a foam applicator to apply soapy water and a squeegee to wipe off the water, taking care of streaks with a chamois or microfiber cloth.
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If you want to do your windows quickly as part of a general exterior house-washing project, though, do the windows separately from the siding. They require different spray techniques. It's almost worth using different machines -- a gas-powered high-pressure one for siding and an electric one with a detergent reservoir for windows.
Requirements for Window Pressure Washing
- Low pressure preferably under 2,000 psi.
- Wide spray pattern: 40 to 65 degrees.
- Ability to mix cleaning solution and water in the spray.
Window Washing Procedure
Set up the power washer by connecting it to a source of water. Before you start it or turn it on, set the nozzle to it's widest pattern or screw on a 40- or 65-degree nozzle. Forty-degree power washer nozzles are white, and 65-degree ones are black. Adjust the pressure to a value between 1,500 and 2,000 psi, and test the spray on a basement or garage window. Spray obliquely -- never perpendicular to the window.
If your windows are under warranty, check with the manufacturer or supplier/installer to confirm that pressure washing will not void the warranty.
Fill the soap reservoir with a detergent recommended by the pressure washer manufacturer. The detergent must be safe for your window frame material. If your power washer doesn't have a soap dispenser, and you want to get the windows as clean as possible, consider washing them quickly using a suitable cleaning solution and a sponge applicator, and rinsing with the power washer.
Many cleaning solutions are toxic to plants. To prevent damage from overspray, wet outdoor plants thoroughly, then cover them with plastic prior to washing your windows. After washing, remove the plastic and wet the plants again.
Keep the tip of the sprayer a safe distance from the window, depending on the pressure. The spray should strike the window at no steeper than about a 30-degree angle. As much as possible, spray from the edge of the pane toward the center; avoid getting spray under the window putty, or the putty may simply fly off.
Turn off the soap dispenser and spray the window with clear water immediately after washing it and before the cleaning solution has a chance to dry.