Your wood deck is probably the focal point of your yard. To keep it looking good, and to protect your investment and simplify regular maintenance, you need to take a little time each year and clean up.

Perhaps the most common cleaning method, as well as one of the most misunderstood, is pressure washing. Pressure washing utilizes a gas- or electric-powered machine to boost water pressure from a source such as a garden hose, and pushes it through a nozzle at very high velocity. Pressure washers are very effective cleaners, but the high pressure can break apart the cells and fibers in the wood and do some serious damage. 

If you want to use a pressure washer, make sure to use low pressure and a wide fan-type nozzle so as not to concentrate the pressure into a damaging stream. For deck cleaning, an equally effective method is to use a garden hose with a spray nozzle combined with a medium bristle push broom.

Another thing you don’t want to do to your deck is use regular household bleach. While these types of common laundry bleaches are very effective at killing mildew, they will do virtually nothing to remove the dirt from your deck. Instead, they can remove some of the wood’s natural color and leave behind an unnatural white or gray tone. As with excessive pressure washing, the use of household laundry bleach can damage and open up the fibers in the wood. This not only results in an unattractive, fuzzy appearance, it can also open up the wood pores for more dirt to enter. 


A much better cleaning option is to utilize a cleaner made specifically for wood decks. Most of today’s cleaners are not chlorine-based, making them both safer and easier to apply, and much better for your deck’s wood. 

Oxygen-based bleach: Deck-cleaning compounds designed specifically for wood commonly contain sodium percarbonate, which is also found in many color-safe laundry bleaches. Sodium percarbonate is a powder that mixes with water to form hydrogen peroxide and sodium carbonate, both of which are very effective at removing gray weathering residue as well as mildew, dirt, and other discolorations. Properly applied, oxygen-based bleach products will go a long way toward restoring your wood deck’s original appearance.

Cleaners containing sodium percarbonate are effective on most types of common decking woods, and will also work on pressure-treated fir, pine, and hemlock.

Oxalic acid-based cleaners: Another common problem with cedar, redwood, and certain other species is a natural resin in the wood called tannin. Tannins, which are water-soluble and a reddish-brown in color, can migrate to the surface of the wood and be deposited there, leaving dark brown discolorations. Tannins can also react with the metal in the fasteners that secure the deck boards, resulting in dark, blue-black stains that can really mar the appearance of the wood.

Oxalic acid-based cleaners are very effective on tannin and iron stains, turning them virtually colorless. Oxalic acid, however, will not clean mildew and some other types of stains, so if tannin is a problem look for a cleaner that is formulated for all types of cleaning – tannin, dirt, and mildew – or use a general-purpose cleaner first, followed by an oxalic acid cleaner specifically for the tannin.

You can find specialized deck cleaning products at many home centers, lumberyards, paint stores, and other retailers of decking products. Before you undertake any deck cleaning task, first determine exactly what you want to achieve, and then match the cleaning product to that goal. Carefully read the manufacturer’s instructions for proper application procedures and precautions for surrounding surfaces. Most importantly, be certain that you follow all of the manufacturer’s instructions and precautions for ventilation, protective clothing, and other safety issues.

Remodeling and repair questions? E-mail Paul at

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