Examine all the deck boards for rot, insect damage, missing knots and severe splitting. Probe the boards lightly with a putty knife to see if there is hidden damage below the board’s surface. Replace any damaged boards.
Drive in any nail or screw heads that have popped up as the boards expand and contract through the seasons. Hammer in the nails or drive the screws back into place with a power screwdriver.
Clean the deck with a power washer set no higher than 1000 psi. Too high a pressure will damage the boards. Wear safety goggles when using the power washer to protect your eyes from dirt and debris that fly off the boards. Aim a fan-shaped nozzle at the boards and between them, dislodging any built-up dirt. Allow the deck to dry for 48 to 72 hours.
Cover any objects, including plants, located around the outside of the deck. Cleaners and stain can harm plants and discolor furniture. Old blankets or cloth drop cloths protect plants while allowing them to respire.
Mix a batch of bleach-based cleaner for decks stained with mildew. Follow the directions on the package for a proper mix, which typically uses water. Scrub any mildew-discolored areas by working the cleaner in with a stiff brush. Allow the deck to dry for 24 to 48 hours.
Mix an oxalic acid cleaner as directed on the package for decks that have grayed or that have stains other than those caused by mildew. Work the cleaner into the wood with a soft brush or a broom. Rinse the deck and allow it to dry completely, typically about 72 hours.
Mix the stain thoroughly, using a paint-stirring stick. Lift the stick slightly as you stir; this helps distribute the stain’s color uniformly throughout the can of stain.
Roll the stain onto the deck boards with a paint roller. Use one equipped with a long extension handle to avoid prolonged bending. Work full lengths of boards as opposed to sections. This avoids overlaps and lines as the stain dries out.
Work the stain between boards and into the surface of deck boards, using a brush. This distributes the stain evenly and gets it into tough-to-reach places.
Allow the deck stain to dry a day or two before allowing traffic on the surface.