Deck Rescue: Renew Your Deck

Overview

If you've been putting off renewing your deck because you think it requires a lot of time, tools and know-how, take heart. In this article, we'll show you how to clean it up fast with the help of a pressure washer and special products that help remove dirt, mildew and old finishes. We'll also show you how to apply a fresh finish, using a foam applicator pad that glides along the wood and quickly applies a nice, even coat. No more messy rollers and brushes.

This process will work on any wood deck, including redwood, cedar and pressure treated lumber (but not on composite decks). The only special tools you need are a pressure washer and a foam applicator pad. The project doesn't require any special skills. Just set aside at least four hours on one day to clean your deck, and another four hours several days later to stain it.

The cost of rejuvenating an average-size deck is about $250, including tools, materials and the pressure washer rental. You'll save several hundred dollars by doing the work yourself. Having your deck professionally cleaned and stained will cost $500 to $1,000.

Rent a pressure washer

A pressure washer will scour away dirt and contaminants ingrained in the wood at the same time it sprays on a deck stripper to clean off previous finishes.

Rent a pressure washer from a home center or rental center (about $40 for four hours, or $70 per day). A pressure setting of 1,000 to 1,200 psi is ideal. Too much pressure will damage the wood and make the wand harder to control.

Rent a unit that allows for the intake of chemical cleaners (deck stripper and wood brightener) so you can spray them on through the wand. Most pressure washers have an intake hose that draws in cleaners from a separate bucket. (Use a plastic bucket. Chemicals in the cleaners can react to metal buckets.)

We used sodium hydroxide as the deck stripper. You probably won't be able to find straight sodium hydroxide, but you can find a deck stripping product with sodium hydroxide as the active ingredient in almost any home center or paint store.

We diluted our stripper to a 50/50 mix with water. Some sodium hydroxide–based strippers are premixed and don't require adding water. More commonly, you need to dilute the stripper with water. Read the label on the container to find out what's suggested for your stripper.

Protect your house and plants

Before you begin cleaning, make repairs to your deck, such as replacing cracked or split boards and broken balusters.

Then heavily douse the plants or grass under and around your deck with water and cover them with plastic. Although most strippers aren't supposed to harm vegetation, it's still a good idea to protect plants and it only takes a few minutes. Once you've finished cleaning the deck, immediately remove the plastic.

Also spray down the siding with clean water to ensure that any stripper that splashes onto the house will easily wash off.

Scour away the old finish

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Photo 1: Clean the railings

Pressure-wash the railings with stripper. Keep the tip 6 to 10 in. from the wood and work from the top down. Spray balusters at the corners to scour two sides at once.

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Photo 2: Wash the decking

Spray one deck board at a time, using a gentle sweeping motion. Avoid sudden stops. Work from the end of the deck toward the exit. Then rinse the entire deck with a garden hose.

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Photo 3: Clean out the gaps between decking

Dig out trapped debris from between deck boards with a putty knife. Spray the deck lightly with a mixture of oxalic acid and water to brighten the wood.

With a 25- or 30-degree tip in the wand of the pressure washer and a psi of 1,000 to 1,200, apply the stripper to the deck, starting with the top rails and working down the balusters (Photo 1). Spray the rails with a continuous, controlled motion. Keep the wand moving so you don't gouge the wood.

Once you finish the railings, start on the deck boards. Wash along the length of the boards (Photo 2). You'll see the grime washing off the wood.

Go over stubborn mildew or other stains a few times rather than turning up the pressure or trying to heavily scour the wood. Later we'll tackle tough stains that won't come out with the stripper.

This stripping process washes away a small amount of the wood's lignin, which is the glue holding the wood fibers together. As the lignin washes away, the fibers stand up, giving the wood a fuzzy appearance. Don't bother sanding off the fuzzy fibers. They will gradually shear off and blow away.

After you've power-washed the entire deck, rinse all of the wood with plain water to dilute and neutralize the stripper. If there's still debris trapped between deck boards, such as leaves or twigs, remove it now (Photo 3).

Brighten the wood

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Photo 4: Clean off overspray

Rinse the siding and windows with clean water at low pressure to remove chemical residue.

A deck brightener will return the wood to its newly sawn color and make it more receptive to the stain. Use an oxalic acid–based brightener, which is available at home centers and paint stores. It works fast, won't harm the wood and is environmentally safe in the diluted solution that you'll use.

Like strippers, some deck brighteners come premixed and some need to be diluted with water. Read the label for the manufacturer's recommendations. We mixed our oxalic acid with an equal amount of water and ran it through the pressure washer's intake hose.

Change the tip in the wand of the pressure washer to a fan tip with a 40- or 45-degree angle. Then set the pressure to about 1,000 psi and spray the deck, once again starting with the top rails and working down to the deck boards. Apply just enough brightener to thoroughly wet the wood.

Oxalic acid will brighten the wood in a matter of minutes and does not require rinsing. But your siding does. Rinse off your siding with clean water at very low pressure (about 500 psi) to wash away any stripper or brightener overspray (Photo 4).

If your wood is cedar or redwood, you'll see a dramatic difference as the wood brightens to its fresh sawn color. Our deck is pressure-treated pine, so the brightening of the wood is less noticeable.

Inspect the whole deck

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Photo 5: Fix loose boards

Sink any raised nails and screws. Replace loose and missing fasteners with screws at least 1/2 in. longer than the original.

With the deck clean, it's easy to spot any areas that need additional maintenance. Drive any nail heads that are popping up until they're flush with the deck boards. Look for missing or loose screws, and replace them with corrosion-resistant screws that are slightly longer than the original (Photo 5). Replace missing nails with corrosion-resistant “trim head ” screws, which are screws that have a small head and resemble a large finish nail.

If lag screws or bolts are loose in the ledger board, rails or posts, tighten them. Inspect the flashing between your deck and house to ensure it's still firmly in place.

Attack stubborn stains

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Photo 6: Scrub stubborn stains

Remove mold, mildew or algae using non-chlorine bleach. Scrub the area with a nylon brush, then rinse with water. For tougher stains, repeat the process with a TSP substitute.

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Photo 7: Remove fastener stains

Drive the heads of stain-causing fasteners below the wood surface. Then sand out the stains using 80-grit sandpaper. Also sand rough or splintered areas.

Although the sodium hydroxide in the deck cleaner will remove most stains and mold, particularly stubborn ones require extra attention.

Use a non-chlorine laundry bleach to remove the stain. (This works especially well if the stain is from mold, mildew or algae.) Apply it to the affected area, then scrub with a nylon brush. Rinse the area with water.

For tougher stains, use trisodium phosphate substitute. Mix the TSP substitute with water and apply it to the stain. Let it sit for a minute or two, then scrub with a nylon brush and rinse with water (Photo 6).

To remove deep stains that don't come out with TSP substitute, let the deck dry. These “bleed” stains are often caused by fasteners. Sand the stains out, using 80-grit sandpaper and concentrating only on the affected areas. Some bleeds may be too deep to sand out. Rough or splintered areas may also need sanding. Spot-sand working in the direction of the wood grain until the surface is smooth (Photo 7).

Wear a dust mask, and sand only if the stain bothers you. You don't have to get every stain out. After all, imperfections are part of an outdoor deck.