There are several different types of deck cleaning solutions available on the market; however, the most effective require using acidic cleaners or power washers, notes This Old House and Lowe's. Acid cleaners, such as oxalic acid use special properties that do not affect the wooden surface and instead attack the hard-to-remove stains. Power washers use cleaners with similar properties, but combine the force of compressed water to help quickly remove old stains.
Oxalic acid is effective in removing black tannis- and iron-based stains, some of which are caused by rusted bolts, notes This Old House. This type of acid is often found in wood brighteners. Oxalic acid is often paired with a bleach-based cleaners to help remove different types of mildew.
Power washing is done using a machine often referred to as a pressure washer. Pressure washers come in all sorts of different sizes, with different limits in terms of power. Larger commercial based units use several thousand pounds of pressure and are powerful enough to strip paint or stains off of walls, cement floors or decks. In order to use a pressure washer, the tank must be filled with the proper cleaning solution. The washer must then be adjusted to the right amount of pressure and it must be evenly sprayed on to the deck, using a swift side-to-side motion.