Winter deck care: fall prep, shoveling and salt

What winter does to a wood deck

Wood decks are flat and fully exposed, which makes them one of the harshest places for wood and finish. The U.S. Forest Service says a deck collects moisture and the weathering process is greatly accelerated; as the wood wets and dries, small checks widen into cracks, and cracks and end grain hold water.

Winter adds freezing to that. Water that gets into a crack expands when it freezes, and snow that melts and refreezes keeps feeding it. Salt adds a separate problem: it can damage the fasteners and hardware that hold the deck together, which is why the advice below is about using less of it and rinsing it off.

Fall prep checklist

This takes an afternoon, and it's the best use of one before the weather turns.

1. Sweep the deck and clear the gaps between the boards. The North American Deck and Railing Association says leaves and debris are slippery and promote mildew.
2. Walk the deck for problems. NADRA's checklist covers the ledger board, posts and joists, deck boards, railings and stairs. Press a screwdriver into doubtful wood, and if it goes in a quarter to a half inch easily, decay may be present.
3. Tighten loose fasteners and pound in popped nails. A rusted or corroded fastener can damage the wood around it.
4. Push on the railings and test the stairs, so you aren't finding a loose one in the snow.
5. Look up for overhanging limbs that could drop on the deck.
6. Move furniture, planters and the grill off the boards, or at least to a spot where you can shovel around them. Anything left on the deck is something snow can pile against.
7. Splash some water on the boards. Purdue Extension's guide to exterior finishes says that if it beads and runs off, the finish is still working, and if it soaks in, the wood needs refinishing.

Our deck maintenance routine covers the full yearly cycle, of which this is the autumn half.

Should you stain before winter?

If the water test says the finish is gone, the instinct is to stain right away. That's the right call when the weather cooperates, and the wrong one when it doesn't. Stain goes onto wood that is clean and thoroughly dry, and every product has a temperature range on its label.

Stain applied to damp wood, or outside that range, can fail to soak in or cure properly. If the conditions aren't there, clean it, check the water test and book the stain job for when they are. Our post on the best time to stain a deck explains what to look for, and how to prepare a deck for staining covers the prep.

That's why our exterior work is scheduled around dry weather.

Shoveling without scarring the boards

Snow is a safety hazard on a deck, and Viance, a maker of wood preservatives, says to remove it from heavy-traffic areas even when the deck has a good sealant. How you do it matters.

• Use a plastic or rubber shovel. A metal shovel can scratch and dent the boards.
• Shovel parallel to the boards. Shoveling across them makes it easy to catch the board edges.
• If you don't have a plastic shovel, leave a thin layer of snow and sweep it off later with a broom.
• Don't chip at the ice. Banging on it can leave dents in the surface.

Viance also notes that the weight of snow and ice could cause a deck to collapse if it hasn't been properly maintained, which is another reason to do the fall inspection.

Salt, ice melt and sand

Every option for ice on a deck comes with a trade-off. Viance advises choosing an ice melt labeled as safe for wood decking, and says that if you use a salt-based product you should rinse the excess away after the ice melts to prevent damage to the fasteners and hardware.

Cold also limits what salt can do. The University of Wisconsin's Center for Limnology says salt is probably ineffective below 15 degrees Fahrenheit, because brine only lowers the freezing point to about that level. On the coldest days, more salt is just more damage.

There's a second reason to go light. Wisconsin Salt Wise, a statewide effort to cut salt pollution, says it takes only 1 teaspoon of salt to pollute 5 gallons of water to a level that is toxic for freshwater ecosystems. The Center for Limnology post adds that about one cup of rock salt treats a 20-foot driveway, and that a leftover pile means too much was used. A few deck steps need far less than that.

The University of Wisconsin suggests sand where you can use it, because it's salt-free. For a deck, Viance warns that sand is abrasive and can scratch it. Use it sparingly where you need grip, and sweep it up when the weather turns.

If you already used salt

Rinse it off. Viance's advice is to wash the excess away once the ice has melted, so it doesn't sit on the fasteners and hardware. Pick a day mild enough that the rinse water won't freeze on the boards, and a plain hose is enough. It is much easier than replacing corroded hardware later.

After the thaw

Wait until the snow is gone and the deck is dry, then inspect it. Look for popped nails and loose fasteners, new cracks at the board ends, mildew where snow lay longest and gray patches where the finish wore off.

Redo the inspection and the water test. If the finish passes, wash off the grime and leave it. If it fails, the deck is ready for a refinish as soon as it dries and the weather settles. Freeze-thaw wears on painted surfaces too, and our post on freeze-thaw and exterior paint covers the rest of the house.

Where we fit in

Deck staining and refinishing is part of our exterior painting work. Smaller exterior projects usually take one to three days, scheduled around dry weather. We start with a phone call, George visits if he needs to see the deck, and you get a written quote with a start date.

We're based in Waunakee and work across Madison and Dane County. Our page on deck and exterior work in Madison has the details, and you can ask for a free estimate whenever you're ready.