Power or pressure washing may seem like a quick and easy way to remove dirt, mold and grime from your home's exterior wood siding, but you must take extreme care to avoid the damage that this machine can cause if used improperly. The condition of your siding and its present coating dictates nozzle and pressure selection. Windows must be tightly sealed against water penetration. External lighting fixtures should be removed and electrical outlets and foundation plants covered to prevent water damage.
Wood Siding Preservation
All types of wood siding, including longer lasting cedar, redwood and cypress, need to be painted every five years or stained every three years. Unprotected wood may absorb water and begin to warp or rot. Power washing, done carefully, can gently clean siding between coatings or prepare the surface of the wood for a new application of paint or stain. Damaged boards exhibiting warp, rot or holes must be replaced before the cleaning and renewal process begins.
Power washing is the first step in preparing siding for repainting. For basic cleaning, a setting of 1500- 1800 pounds per square inch (psi) is recommended. This pressure is sufficient to remove dust, dirt and spiderwebs. If loose paint is present, use 1800 psi to remove it. Professional power washing machines use color coded nozzles with quick disconnect capability. Use the siphoning action of the black nozzle to apply house wash or mildew protectant. Clean with the green 25-degree nozzle. Remove paint with the yellow 15-degree nozzle.
The condition of the stained siding dictates how to clean it. Visible mold growth must be removed with bleach and water or specialty products that can be applied with the pressure washer. Old stain turned into a powder and burned up by sunlight requires pressurized water only to remove it. If the new stain you intend to apply is lighter than the old, all of the old stain must be removed. For best results, use 2,000 psi with a white 40-degree or green 25-degree nozzle.
Turn off electrical power to all external fixtures and electrical outlets. Avoid spraying directly into soffit or gable end vents. Spray at a distance of 2 to 3 feet to avoid damaging the wood. Apply cleaners and/ or pressurized water from the bottom up, and rinse from the top down. Move the nozzle with the grain of the wood, and avoid stopping in one spot. Do not powerwash windows and doors. These delicate areas must be cleaned by hand.
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