Algae build-up is a common problem for wooden decks. While the blooms are harmless to the wood itself, they can coat your deck's surface with a fine, green film that is quite slippery and dangerous when dampened by dew or rain. Washing away the algae with soapy water may not fully kill the growth, and although power washing can remove it, the force of the spray may harm your decking. First eradicate the algae, then dry the wood. Sealing the deck is also effective in fighting algae.
Clear everything from the deck, especially plants. Cover plant life surrounding the deck with plastic tarps as the cleaning chemicals can kill them.
Sweep the deck with a bristle broom, removing debris and dislodging large areas of algae growth.
Mix 1 cup of water and 1 gallon of bleach in a metal bucket. Scrub the deck surface with rags soaked in the bleach solution, following the natural grain of the wood.
Use the bristled-brush for stubborn growth. Rinse with a hose and spray nozzle. Allow the deck to fully dry for at least 48 hours.
Seal the deck with a wood preservative, available at builder's supply and home improvement centres. Apply according to directions on the can. Further retard the growth of algae by keeping the deck swept and free of debris.
Prune overhanging tree branches and pull back shrubbery to assist in preventing future algae growth. Algae grow and reproduce on moist surface conditions. Allowing the sun to continually penetrate through to your wooden deck will forestall the growth of algae and moulds.
Algae can lay dormant and return when environmental conditions are favourable. That is why chemicals are recommended to kill their growth. If you are chemical-adverse, however, products such as oxygen bleach, organic fatty acids or mere soap and water, coupled with diligent maintenance, can also keep algae at bay.