Karcher 2nd Story Soap & Spray Pressure Washer Nozzle Kit (4000 PSI)

Dan,

Mildew is a mold- it penetrates the surface and "hangs on" tight; it stains and it's tough to clean. Pressure washer-safe detergents need to be fairly mild so they don't damage the seals in your pressure washer's pump, but that means they may not be strong enough to totally eliminate established mildew and mildew stains.

Some folks will use a tank sprayer (like you'd use for weed killer) to apply a mildewcide or harsher chemical like bleach/water, TSP or Jomax, then use their pressure washer to rinse it off after it's had a chance to kill the mold- but it may not always lift the stain.

Please be careful with mildew-killing chemicals: water and protect your landscaping, keep pets & children away, be aware that a breeze can blow the spray onto cars and furniture. Be sure to wear protective clothing & eyeware, and don't breathe the spray.