Plants like trees and bushes produce airborne sugars that drift through the air and stick to vinyl siding. This nearly invisible layer of sugar is a food source for mold. Dust and dirt can also stick to the vertical sides of vinyl siding, and these are also food sources for mildew. Follow the advise below for effective cleaning and mold removal.
Some vinyl siding manufacturers don’t want pressure washers used on their product, while others allow them, but have limitations on the amount of pressure and the cleaners that can be used. Most will caution against the use of pressure washers around any opening in the wall, such as windows, doors, electrical wiring, and plumbing. Do not aim the power washer upward as water may be driven behind the siding.
The best way to clean vinyl siding is to rinse it down with a regular garden hose equipped with a nozzle. Set the nozzle to a medium misting spray. Never use a forceful direct stream of water, as it can penetrate behind the vinyl siding. There are many homes covered with vinyl siding that do not have waterproof membranes that cover the frame walls. The wood sheathing and framing lumber can get wet easily if you direct water at the edges of vinyl siding, seams where two pieces of siding overlap, at inside and outside corners and next to windows and doors.
Vinyl siding is designed to shed water falling from the sky, not water that is shot up from the ground. Always rinse off the siding pointing the hose down towards the ground. Never aim a hose up at vinyl siding as it can cause massive amounts of water to seep behind the siding.
Regular dishwashing soap will do a fantastic job of cleaning vinyl siding. Squeeze a generous amount in a bucket, and add warm water to make a frothy mix of soapy water. I like to pour this water into a hand-pump garden sprayer to apply it onto the vinyl siding once it has been rinsed with clear water. Small spots of mold and mildew can be handled with cleaners such as Fantastik® or Windex®. For larger sections, a solution of vinegar (30%) and water (70%) has proven successful. Alternatively, you also could try the following solution: 1/3 cup (2 2/3 ounces) powdered laundry detergent (e.g., Tide®, Fab®, or equivalent), 2/3 cup (5 1/3 ounces) powdered household cleaner (e.g., Spic & Span®, Soilax®, or equivalent), 1 quart (32 fluid ounces) liquid laundry bleach, and 1 gallon (128 fluid ounces) of water.
Wash vinyl siding with a soft cloth or ordinary long-handled, soft bristle brush. For textured surfaces, use only a soft bristle brush to keep the grooves in the texture stain-free. Purchase a soft brush from a recreational vehicle (RV) dealership. They sell special brushes used on long poles to clean the sides of RVs. These brushes are superb tools to use on dirty vinyl siding. Once the vinyl siding has been coated with soapy water, dip the brush in the soapy water and use side-to-side motions to remove dirt.
Start cleaning from the bottom and go up as far as you can reach. I suggest cleaning an area about six to seven feet wide at a time. Immediately rinse the area you cleaned — you never want the soapy water to dry on the siding before it can be rinsed off (best to work in the shade if possible). Proceed up the wall until you get to the top alternately washing and rinsing. As you get higher, always make sure you rinse all dirt all the way down the siding to the ground.
Never use chlorine bleach as an additive to your soapy water solution. Chlorine bleach is a deadly toxin for any and all vegetation around your home. The chlorine ions soak into the ground and kill the roots of the plants, grass, trees and bushes.
If you feel compelled to use a bleach to help kill the mildew, use oxygen bleach. Oxygen bleach is non-toxic, has no odor and it injects oxygen into the soil.