How should I clean up my deck and outdoor wood after the winter rains?

Let it dry out first

The urge after a wet winter is to get out there the first sunny weekend. Give it a little longer. Wood that has been wet for months needs a week or so of dry, breezy weather before it is ready to clean and test, and the marine layer in spring can keep north-side and shaded wood damp well into the afternoon.

You will know it is ready when the boards look uniformly light in color by midday and the gaps between them have opened back up. Wood that still looks dark along the edges is still holding water.

Sweep, clear, then wash

Start by clearing the gaps between deck boards with a putty knife and sweeping or blowing off everything that collected over winter. Then wash. An oxygen-bleach wood cleaner mixed as the label directs, left to sit for ten or fifteen minutes and worked with a stiff deck brush, lifts the gray film of mildew and dirt that winter leaves behind. Rinse thoroughly with the hose.

If the wood has grayed or has dark water stains, follow with an oxalic acid brightener, which restores the color and neutralizes the cleaner. Composite gets the same cleaner and brush, no brightener needed. A pressure washer is optional and only on a wide fan tip at low pressure, kept moving; held close it tears up the soft grain and leaves a fuzzy surface.

Look for what winter did

Clean wood shows its problems. Walk the deck slowly and look for boards that have cupped or lifted, screw heads that have popped above the surface, new checks that run deep enough to catch a fingernail, and dark areas that stayed dark after everything else dried.

Then get under it or alongside it with a screwdriver. Press the bottom of each post, the stair stringers where they meet the ground or concrete, the ends of joists, and the ledger where the deck meets the house. Sound wood resists; rotted wood takes the tip easily. Look at hangers and bolts for rust streaks. On a fence, push each post and look at the bottom of the boards where they sat in wet mulch.

• Boards cupped, lifted or split beyond a surface check.
• Fastener heads standing proud or rust streaking down from them.
• Soft wood at post bases, stringers, joist ends or the ledger.
• Green or black growth that came back within weeks of cleaning, which points to a water source.

Decide what gets a coat this year

Once the deck has had two or three dry days after washing, do the water test. Boards that soak water in get a maintenance coat of penetrating finish; boards that still bead can wait. On many coastal decks that means the sunny half gets oiled this year and the shaded half next year, which is fine with a penetrating product.

Finish only fully dry wood. Spring in North County can tempt you with a warm week that is followed by a damp one, so check the forecast and give yourself two clear days after the coat goes on.

Pergola and fence get the same treatment

On a pergola the tops of the beams and rafters catch the winter grime and the mildew, so that is where to wash and where to test. Protect whatever is under it from the cleaner. On a fence, wash the shaded face as well as the sunny one; it will not need finish as often but it is where the mildew lives.

Spring is also when sprinklers come back on. Before they do, check that none of them hit the fence, the deck or a pergola post. A sprinkler that wets wood every morning undoes every bit of this work.

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