Late spring: Wash the deck

Aside from general dinginess, one of the sure signs a deck needs washing is a film of mold and grunge. Left unchecked, mold and dirt and can trap moisture and cause rot.

Begin cleaning your deck by removing debris from between deck boards using a putty knife. (For a makeshift extension that’s a real knee-saver, try pushing the handle of your putty knife into a length of 1¼-inch PVC pipe. Some putty knives squeeze right in.)

Or, buy a pole-type groove and crevice cleaner. Pay special attention to the areas where deck boards cross the joists — the structural members underneath the decking. Thoroughly sweep the deck.
 
For a wood deck, use a standard deck cleaner — about $20 for 250 sq. ft. coverage. Or, make your own with a half bleach, half water solution. Choose a cloudy day when the decking is cool and the sun won’t evaporate the cleaner. Protect all shrubs and plantings with plastic sheeting. Apply the cleaner according to the manufacturer’s instructions.

Once the decking is cleaned, tackle the railing. Working from the bottom up, apply the cleaner, scrub, and then rinse. Working from the top down splatters the cleaning solution onto dry wood where it can double-bleach the surface, leaving marks that don’t go away when the lower area is washed. Working from the bottom up means you’ll be splattering onto a wet surface where the cleaner is diluted, leaving no marks.

For composite decks, use a cleaner specifically formulated for use on composite material. Scrub with a soft brush. Do not use a pressure washer — it can permanently damage the decking and will void any warranty. Remove rust and leaf stains with a deck brightener containing oxalic acid. Attack grease and oil stains with a commercial degreaser and detergents. Mold and mildew can be kept under control with the use of a deck wash solution twice a year.

For vinyl (cellular PVC) decking — the closest thing to a maintenance-free material — you’ll only need to use warm water and a mild soap to remove mold, mildew, and dirt. Scrub in a circular motion using a stiff broom, then rinse thoroughly.

Late spring: Seal the deck

The finish on your deck may be so woebegone that it’s obvious it needs resealing, but if you have doubts, try the water test. Splash some water onto the deck. If it beads up, all’s well. If it soaks in, it’s time to wash and reseal the deck.

Wash the deck as described above and allow it to dry for 48 hours before sealing. Use a pole sander equipped with 80-grit paper to remove any furriness caused by washing.

Sealers and stains are available at home improvement centers for about $30/gallon — enough to cover 250 sq. ft. of decking. Your finish options include:

  • Clear sealer that lets the wood’s natural grain and color show through
  • Toner that adds a bit of color but fully reveals the grain and provides some protection against sunlight (ultraviolet or UV light)
  • Semi-transparent stain that tints the wood, but lets some grain show
  • Solid stain and opaque color that seals weathering damage and completely covers the grain

Expect to recoat clear sealers and toners annually. Recoat stain finishes as needed (every other year is a good routine), using the same or a slightly darker color. Be sure to wear gloves, a safety mask, and eye protection when applying stain and sealers. Use a roller to apply the sealer to the decking, covering three or four boards at a time. Use brushes and small rollers for railings, planters, and benches.

Some composite decking can be stained to restore its color. Be sure the product is intended for composites. Don’t expect the same density of color that you would achieve with wood. Deck sealants aren’t required or recommended.

Midsummer: Inspect and repair your deck

When the weather is warm and dry, it’s a good time to give your deck’s structure a close inspection. Pay particular attention to any areas within 6 inches of the ground or close to sources of water, such as downspouts and planters.

Look for signs of rot by probing structural members with a flat-blade screwdriver. Begin by checking stairs, especially where the stringers (the saw-tooth notched pieces that support the steps) meet the ground. Also check each perimeter post. If you can push the screwdriver a quarter-inch or more into a suspect area, you probably have rot.

Areas of rot that are no bigger than a silver dollar can be removed with a chisel and the hole can be treated with wood preservative. Larger areas may require the structural member to be replaced. Consult a professional carpenter or builder for an estimate for repairs.

If the underside of your deck is accessible, use a flashlight to inspect joists, posts, and beams. Pay special attention to the ledger — that all-important piece of framing that attaches the deck to the house. An estimated 90% of collapsed decks resulted from the failure of the ledger. However, not all decks have ledgers. Some are free-standing — a beam and posts located within a few feet of the house indicate a free-standing deck system.

The ledger should be attached with lag screws, not just nails. The flashing — the metal cap that covers the top of the ledger and prevents moisture from getting behind the siding — should be free of rust and holes. Check all the hardware underneath, especially joist hangers, and replace any that are seriously rusted. Probe for signs of rot on the posts and joists. If anything looks doubtful, call in a pro to provide an estimate for any needed repairs.
 
If a framing member can’t be easily removed and replaced, reinforce it. For example, if a joist shows areas of rot, you can add a splint of comparable pressure-treated lumber along side it, attaching the splint with two or three 3-inch deck screws every 12 inches. Then chisel away the rotten area and paint the raw wood with preservative.

Topside, look for cracked or rotten decking boards. Not all cracks are a structural threat, but they’ll get worse with time. If you find damage, replace the piece. Areas of cupping can be sanded down.

Give the railing a good shake to be sure posts are not loose or damaged — loose connections may be remedied by drilling pilot holes and adding galvanized lag screws. Look for cracks that, over time, may have developed around fasteners such as nails or screws. To remedy, remove the fastener and seal the crack with an exterior-grade adhesive. Then, drill a new pilot hole and add a new galvanized deck screw.

Early fall: Preventive measures

If the decking was nailed, you’ll likely find some nail heads popping out. A short-term solution is simply to pound them back in using a hammer and a thick nail set. For a longer lasting solution, pull out each protruding nail and drive in a deck screw slightly longer than the nail. (When pulling out the nail with a hammer or pry bar, use a scrap of wood as a fulcrum for greater leverage and to avoid damaging the deck.) If a nail only slightly protrudes, you may do more harm than good trying to pull it out. Pound it home.

To slow mold, moss, and rot, keep nearby bushes and trees cut back at least 12 inches from the deck. Don’t let leaves and other debris pile up in corners. Move planters, chairs, and tables occasionally to avoid discoloring the decking. Keep nearby gutters and downspouts in good repair.