UV radiation and acid rain are the primary causes for the surface of vinyl siding to deteroriate. This results in the vinyl becoming dull and brittle, leaving a rough surface that absorbs moisture, making it a perfect breeding ground for the growth of mold, mildew, and fungus.
To determine whether blackish areas are mildew or just dirt, take a small amount of household bleach and apply it to the vinyl siding with a sponge. If the black spots disappear, it is most likely mildew. If they don't go away, the discoloration is probably just dirt and should easily be removed with a non-phosphate detergent.
When detecting the growth of mildew on vinyl siding, it is important to remove it as quickly as possible. The faster you are in removing it, the easier it is to clean. Mold and mildew will spread very quickly, especially in damp climates, and could ruin the vinyl siding permanently if not removed soon enough.
If you choose to do this work yourself, start by scrubbing any mildew from the vinyl's surface prior to power washing. Use both hands when operating the equipment and never use it while standing on a ladder. For high areas, you may be able to rent 6-12 foot extension wands, but be aware that these are difficult to handle and dangerous. Start with the nozzle about 3-5 feet from the wall and work your way closer until you feel the spray is strong enough - but not too strong. Never get closer than 12 inches from the siding as you may damage it and avoid aiming it upward as you may push water behind the siding. Remember, you are working with high pressure, so never point the nozzle at anyone and always wear safety glasses. Always keep the wand, water, and yourself away from any electrical wires or devices.
If you have a wide spread mildew problem, or your home is very large, it is much easier and safer to let a professional power washing contractor to do this work for you. These contractors are familiar with the correct detergents and methods to properly remove mildew, restoring your vinyl to a like-new appearance.
