Here is a very simple home made recipe for all around cleaning that works great on decks. If you want to finally get rid of that mildew and algae,now is the time. This recipe was handed down from a older gentlemen who was a painter at a country club I met in 1971.
Mildew and algae are usually problems in areas that have a high level of moisture and it typically grows on the north side of the house or shady areas. Its generally an eye sore but left uncheck it can be a hazard. It will create a slippery spot just like a sheet of ice and if you have children or elderly folks its best to remove this problem.
This simple recipe is TSP or trisodium phosphate (TSP can be purchase at your local hardware store) and warm water with a little bleach. The TSP comes is a white power that is a little course and is mix in warm water to help it dissolve.
Bleach is use to destroy micro-organisms such as mildew and algae.
The generic cleaning composition is 1 to 1 1/2 cups TSP to two gallons of warm water,if there is a lot of mold I would add 1/2 cup of household bleach (do not use commercial bleach which is stronger). I generally make my recipe on the lighter side first. I can always make it stronger (stronger means 1 1/2 cups of TSP) or wash the area twice if I want to be careful.
Hose down the deck with water to get the pores of the wood to open up,this makes it easier to clean. With a scrub brush attach to a pole start to applied the cleaning solution on the deck, work a small section at a time. When you are satisfied with the results hose off the cleaner. If the mold has been on the deck for a long time you might not get it all off,so try to be happy with the results you are getting.
Do not try to make a stronger recipe by adding more TSP or bleach,if its necessary to clean the deck again,do so.
Never use bleach on a cedar deck,this will strip away its natural colors. If you are cleaning mildew and algae off of a cedar deck ask your local paint store what product they recommend. My personal preference is to just use a pressure washer with cold water.
Make sure you are careful when pressure washing cedar because its such a soft wood.
Take your time and preparation is the key for a successful job.