Using Pressure Washers for Cleaning an Outdoor Deck.To clean a large deck or one with hard-to-clean features like benches and planters, consider renting a power washer. Request a washer having a pressure rating of 1,000 to 1,500 pounds per square inch. Use a nozzle with a relatively wide arc for general cleaning -- 40 degrees is a standard size -- and a narrower one, usually 15 degrees, for between deck boards. Aim carefully when using the narrower nozzle and avoid using a nozzle narrower than 15 degrees. The spray can damage the wood. All pressure washers can break windows and damage plants with direct spray.
 

Ordinary washing can brighten most decks. To clean an outdoor deck, use a stiff-bristle brush dipped in a solution of warm water and strong detergent or trisodium phosphate, the high-phosphate powder that can be used where it is legal. Mix the solution according to the directions for heavy-duty cleaning or use a half-cup of detergent for each gallon of water. To avoid irritation, wear rubber gloves and goggles.

Use a putty knife or old handsaw to clear debris from the spaces between deck boards. The spaces allow water to drain quickly from the deck and provide thorough air circulation, which retards decay and molds.

When using a pressure washer, wear safety goggles. Spray in line with the grain, holding the nozzle at a slight angle about six inches above the surface. Work slowly at a uniform rate and overlap parallel strokes.

An extremely dirty deck may require washing with an unrestricted cleaner. Most cleaners are caustic compounds that work by eating away the surface of wood to expose fresh cells.
Application is by spraying, rolling or brushing. Be careful to follow the directions and precautions. Wear protective clothing and cover plants and grass with plastic sheeting.