A simple solution of mild soap and a pressure washer will help clean your deck or porch of surface mold and dirt. Keep the pressure low and use a 45-degree fan movement and keep the wand moving so you don’t damage the surface.
There are also specific wood or treated wood products at your local hardware dealer that are made especially for this job. Keep in mind that surface mold in no way affects the decay-resistant properties of your project. After cleaning, a water repellent or a stain with an added water repellent can be applied to help reduce checking and cracking of the wood.