Rather than using a chlorine bleach. I recommend using a non-chlorine washing powder made of sodium percarbonate and sodium carbonate.
- "Oxygen powder" or "washing powder" is very similar to baking soda, and can be purchased in the laundry aisle of your local grocery store for around $1 per pound.
- A 100 square foot deck would require less than 2 pounds of washing powder.
How I do it
I like to first wet the entire deck with a 9 to 1 water to washing powder solution.
- Immediately after, while the deck is still wet, I lightly apply washing powder by itself (using a salt shaker method), attempting to cover the entire deck with a very thin layer.
- Don't worry if you don't get total coverage.
- Let the this solution sit for at least 30 minutes, preferably during the day.
- Follow up with a thorough scrubbing. I like to use a hose/scrubber attachment.
With a little elbow grease, your old deck should look as good as new.
Preserve the cleaned wood
After the wood has had a chance to dry, you can apply natural wood stabilizers and/or stains to further the level of protection from the elements.
For more information:
Read "Can I use boiled linseed oil on wood during the rainy season?" a Q&A answered by Florian Speier.