Refinishing a Pressure-Treated Deck

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Repairing a Wooden Deck

Deck Clean-Up and Repair

Dear NH,
I want to refinish my pressure-treated deck. The boards were not too bad, but they were very dirty. I power washed the deck, but now there are weird grooves in the boards. It appears that the water cut into the boards. Is there anything I can do to save the deck?
FB from Cleveland, OH

Power washers are great timesavers, but they can cause tremendous damage if not used carefully. Many surfaces are just too soft to stand the concentrated power of power washing. Cedar siding and pine deck boards are two examples. Pressure-treated (PT) wood is typically yellow pine, which is a sturdy breed of pine but softwood nonetheless. As the wood ages from the weather and the sun, the surface begins to develop soft spots along the grain. Power washing can blast out this soft material, leaving deep ridges in the boards.

A repair can be done, but it will require a little work. First, countersink all nail heads at least an eighth inch into the wood with a sturdy nail set. Then, you can use a belt sander or (to save your knees) a floor sander to flatten the ridges. Start with a fairly rough grit. 50 should be a good place to start. You can leave the floor rough or sand again with 120 grit for a smoother surface. Most rental places will allow you to return unused sanding belts so get an assortment if you want to experiment!

This same procedure can be used to refresh worn handrails, but use the belt sander. The floor sander may be a teensy-bit heavy for anyone but the Incredible Hulk!

Because of the health danger of the cyanide-based preservative in PT wood, collect as much of the dust as possible. Utilize the built-in dust collection of the sanders and also vacuum or sweep up any residual dust. Lay tarps under or around the deck for even more protection. A NIOSH-approved respirator is also advised. Needless to say, try to plan this job for a dry day with little wind.

If you don't want to repeat this laborious task in a few years, keep your deck protected with a quality finish that contains both UV blockers and a mildewcide. You should recoat it at least once every two years or whenever water no longer beads up on the surface.

Don't misunderstand. Power washing is not forbidden! Most power washing problems are due to over enthusiasm. Use the least amount of pressure that gets the job done!

A great alternative to the "power" approach is a chemical deck-restoring product. These are applied with a low-pressure garden sprayer, allowed to work for a few minutes, and rinsed off with a garden hose. Some brushing may be required on really disgusting, filthy decks! Yuck!

Even with these products, though, a neglected deck may require a little sanding to return it to almost-like-new condition!

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