How often should you pressure wash?
A typical Northwest homeowner should power wash their walkways, sidewalks, patios, and driveways at least once a year, businesses with heavy traffic should pressure wash their store front at least two or three times a year depending on ongoing traffic.
Pressure Wash Everything? No.
Hard surfaces such as stone, concrete, and asphalt can easily withstand annual power washing, but soft woods and composite decking should generally not be pressure washed. There is a significant difference between "pressure washing" and "washing off with a hose." It is best to avoid high pressure washing of exposed wood since it will lift the grain and make the surface less smooth. A less smooth surface increases the rate at which mold and mildew will develop.
How do I deal with wood deck and certain types of patios?
As mentioned above, the pressure you need to wash your deck surface is rarely more than 1500 pounds per square inch (PSI). This is still enough pressure to do damage to soft wood; and enough pressure to leave lap marks on most composite decking. Remember: less is more when it comes to pressure washing. The pressure washer serves a mechanism to remove embedded dirt and other contaminants.
Excessive forces on the wood will remove much more than those pollutants you want removed The operators hand will be the only measure as to when too much pressure has be exerted. Having said that, it is the cleaner that should do most of the work in removing the dirt.
Alternatives to Pressure Washing?
A soft or low pressure wash using a good quality detergent is a viable option to pressure washing. Using biodegradable soap and rinsing nearby foliage is a must.
There are also chemical treatments such as Wet-n-Forget that can be applied to dry surfaces and then, over time, remove mildew.