How to Refinish a Deck with Mold

Remove all furniture and other items from the deck. Cover plants and shrubs near the deck with plastic sheeting. This measure prevents damage from any chemicals used in the deck refinishing process.

Use a knife or similar sharp object to pick out all debris from between the boards on the deck floor. Inspect all the deck screws to ensure they are below the surface. Replace any screws to secure loose boards.

Mix a few drops of liquid laundry detergent in a gallon of water. Scrub this solution on the deck with the grain of the wood, using a scrub brush. Follow it with a mixture of one part household bleach to four parts water. Scrub the decking again with the bleach mixture, working especially hard to remove deck mold spots. Let the bleach mixture sit on the decking for 15 minutes. Rinse the deck thoroughly with a sprayer attachment on a garden hose. Allow the deck to dry.

Sand the deck with a hand sander or a floor sander going with the grain. Start with medium-grit sandpaper for the first pass, and then finish with fine-grit sandpaper. Use fine-grit paper to sand the deck railing and banisters by hand. Rinse the deck thoroughly and allow it to dry completely.

Select a wood sealer or stain with mildewcide to finish the deck. This ingredient helps prevent mold from growing again on your cleaned deck. Look for a product that soaks into the wood and that provides ultraviolet (UV) protection.

Stir the sealer or stain. Do not shake it or it may have bubbles that affect the way the finish looks. Use a paint roller or sprayer to apply the product to the deck. Work the product into the wood with a paintbrush. Do not overlap the product and do not allow it to puddle on the deck. Apply a second coat, if desired. Allow the sealer or stain to dry for the amount of time recommended by the manufacturer. Times can vary based on temperature and humidity.