In the last few weeks I have done a couple of deck restorations for my Denver-area carpentry clients. The first was a relatively new hardwood deck, which I've cared for in the past. It had been three years since I was last there performing routine deck maintenance. In our climate, this is a bit long for the oil-based products I prefer to use. I oil my own hardwood deck about every 18 months — spring one year, fall the next. I can oil my entire 650 sq ft deck in 6-8 hours. One afternoon’s work is not that big a time commitment.

My client's deck, however, had not seen the same level of preventive care that I perform on mine; mainly this has to do with snow removal. Her site and roof pitch result in snow piles lingering on the deck for many consecutive months. This higher moisture load results in more soiling and mildew.

Here's how I clean even heavily soiled decks -- the right way.

Use oxygen-based cleaner

My preferred brand of cleaner for deck maintenance is Penofin’s, whose primary ingredient is Sodium Percarbonate. When mixed with water, it yields Hydrogen Peroxide and Soda Ash. This hydrogen peroxide further breaks down into water and oxygen, and as far as “green” cleaners go, it is one of the best. Unlike bleach solutions, the pH of this oxygen-based cleaner is much more wood-friendly. It also does a good job of lightening a wood deck and getting rid of that weathered gray look. Peroxide is a great mildew cleaner as well.    

Sodium Percarbonate-based cleaner comes as a dry powder that is mixed with water before use. I like to mix up a gallon or so at a time in a 5-gallon utility pail. I then transfer the solution to a garden pump sprayer to apply it to the deck surface. TIP: Take your time with the mixing phase and don't mix directly in the sprayer, to keep the un-dissolved bits from clogging the sprayer. 

Before applying the cleaner, I hose the wood down with water. This product works better when the surface is kept wet. A few minutes after application, the deck will foam up like when hydrogen peroxide is applied to a cut or wound. To ensure a more thorough cleaning, I scrub the surface with a deck scrubbing broom. A rinse with a garden hose removes the loosened dirt and grime, and then the deck is looking refreshed.

Power washing tips

In some cases I will use my power washer to rinse away the dirt and grime, as some of my clients are on wells and their water pressure is a bit low. If power washing, be extremely careful; a power washer can quickly damage wood when used too closely. With a hardwood deck, this is less of a concern, and can sometime speed the overall process. With softwood decks, the scrubby brush and garden hose work just fine, though a bit of elbow grease is involved.

Brighten the deck

The next product in Penofin’s cleaning regime is the “brightener,” an oxalic acid-based product, which removes some of the tannin staining so common in certain wood species. Like the cleaner, this is a dry powder that is mixed with water and sprayed on. Here again, it's important to keep the surface wet. The acid nature of this second product brings the pH of the wood back into balance, which will prolong its life. 

Once the cleaning steps are complete, I allow the deck to fully dry a few days before applying the final oil-based product.

Restore a deck after years of no care

The second deck I restored recently was made of softwood and had seen many, many years of no care at all. After I cleaned and oiled it (with Penofin’s Verde line of Zero VOC oil, which is made from 100% sustainable components) the deck now looks presentable and ready for the next BBQ.  As an added treat, the rough weathered railings on this deck were sanded down to a splinter-free state. The patina of near 20 years of Colorado sun still shines through. With some more regular deck maintenance, this beauty can be preserved for years to come.

Hire a professional for expert wood deck maintenance.

Updated December 24, 2017.