It costs an average of $165 to pressure wash a 500-square-foot aluminum deck. Metal decking, usually aluminum, withstands high-pressure washing and is quick and easy to clean, as dirt, mildew, and grime doesn't adhere well and washes away quickly. Pros often use a detergent in the washer for metal, as it restores the surface quickly and effectively.
Wood
Pressure washing a wood deck typically costs $190 for 500 square feet. Wood is porous and natural, therefore, unless you've got an exotic hardwood deck like tigerwood, your deck is fairly fragile. A misused pressure washer can strip away paint and sealant and can damage the wood itself. Therefore, it takes a professional more time to pressure wash a wooden deck safely—hence, the higher cost compared to cleaning a metal deck.
If you want to paint or stain your deck, you'll need a pro to pressure wash your deck to peel away old paint and stain layers without damaging the wood itself. This prepares the surface for the new application of stain, seal, or paint.
Composite
It costs around $210 to pressure wash a 500-square-foot composite deck. Composite cannot withstand sustained spray from a high-pressure washer and, like wood, should only be washed at 1,500 PSI or lower. Composite costs more to pressure wash than other decking materials because, for the cleaning to be effective, the deck must be scrubbed lightly throughout the cleaning process—pressure washing alone is not enough.