How do I know when my deck needs to be resealed?

How to do the water test

Pick a few boards in the sunniest part of the deck and pour on a cup of water, or flick a handful from the hose. Watch for a minute or two. A finish that is still working holds the water in beads or shallow puddles that stay clear. A finish that is worn lets the water darken the wood and disappear into the grain, sometimes within seconds.

Do the test on a dry deck, at least two or three sunny days after rain or a heavy marine layer. Damp wood will not take in water the way dry wood does, and it can fool you into thinking the finish is fine.

• Beads up and stays clear: the finish is fine. Test again in a few months.
• Darkens slowly over a couple of minutes: plan a maintenance coat this season.
• Soaks straight in and the surface looks fuzzy or gray: clean, brighten and recoat now.

Other signs the finish is wearing out

Color is the next clue. A pigmented oil or stain fades toward gray as the UV blockers in it break down, and the change shows first on the boards that catch afternoon sun. Run a hand across the surface. Protected wood feels slightly waxy or smooth; worn wood feels dry and chalky, and on softer species like redwood or cedar you may feel the grain standing up.

Small black specks are mildew getting a foothold in fibers the finish no longer protects. Fine cracks along the grain, called checks, that look lighter inside than the surrounding board mean water has been getting in and drying out over and over. None of these mean the deck is failing, but together they say the finish has done its job and needs renewing.

Test several spots, not one

A deck does not wear evenly. South- and west-facing boards, stair treads, the top rail and the open area where nobody sits can be ready for a coat a full season before the boards under the dining table or along a shaded wall. Near the coast the gap is wider, because the marine layer keeps the shaded boards damp while the sun bakes the open ones.

Check the rail cap too. It takes sun from above and hands and drinks all summer, and it is often the first wood on a deck to gray. On a pergola the top faces of the rafters and beams are the equivalent spot, and a quick splash from a hose while you are on a ladder tells you what you need to know.

If the sunny boards fail the test and the shaded ones pass, you do not have to coat the whole deck. A penetrating oil can be touched up board by board without lap marks, which is one reason we favor it on horizontal surfaces here.

Why waiting for peeling is a mistake

Penetrating oils do not peel. They wear away gradually, so by the time a deck looks obviously bad the wood underneath has been unprotected for months. Film-forming stains and clear coats do peel, and once they do the only real fix is stripping, which is a big, messy job.

Catching the finish while it is thin is the difference between an afternoon of cleaning and one thin coat, and a weekend of cleaner, brightener, sanding and two coats. It also keeps water out of the fasteners and the end grain, which is where rot starts.

What a maintenance coat involves

Clean first, always. A wood cleaner and a stiff brush lift dirt, pollen and mildew; a brightener restores color and opens the grain. Rinse well and give the deck two full dry days. Then apply one thin coat of the same type of finish that is already on the wood, back-brushing so nothing pools. Give the ends of boards and any cuts a second pass, because they drink finish faster than the faces.

In Carlsbad we can do this almost any month, as long as there is no rain forecast for a day or two afterward and the boards have had time to dry out. Avoid the hottest part of a summer afternoon, when the finish flashes off before it can soak in.

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