A Full Guide to Power Washing the Deck
Deck seen too many summers? Give it a new lease on life. We'll teach you about power washing your deck as well as how to put a new finish on.
A full day
IntroductionDeck seen too many summers? Give it a new lease on life. We'll teach you about power washing your deck as well as how to put a new finish on.
- Foam paint pads
- Pressure washer
- Deck stain
- Oxalyc Acid
If you’ve been putting off power washing 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. You’ll be power washing your deck in no time.
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 deck cleaner from a home center or rental center. 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 power washing your deck, 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.
Project step-by-step (11)
Scour away the old finish
Clean the railings
Begin by power washing the deck 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.
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.
Clean out the gaps between decking
After the first round of power washing your deck, it’s time to tackle the seams. 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
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
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
Scrub stubborn stains
The next step in power washing you deck may require a little elbow grease. 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.
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.
Apply the finish—finally!
Stain the railing first
Now that you’re done power washing your deck, you can move on to the finish. Apply stain to the top rail, then the balusters and the posts. Work from the top down. Stain one section at a time, using a foam applicator pad. Brush out drips as you work.
Use an extension pole on the decking
Stain the deck boards using a foam applicator pad with an extension handle. Stain the full length of two or three boards at a time, working with the grain.
Spray bottle applicator
Spray on the finish in hard-to-reach areas or surfaces that are difficult to cover with a paintbrush. Use a wide spray to avoid streaks. Work stain into crevices and narrow areas between balusters and posts with a paintbrush. The deck will need a minimum of 48 hours to dry after the cleaning. If it rains, wait two more days for the wood to dry. Avoid staining in high heat, high humidity and in direct sunlight. Perfect conditions are an overcast day with the temperature in the 70s and no possibility of rain.
Start by staining the top rails and working down the balusters and posts (Photo 8). Run the applicator pad down the length of the wood, applying the stain in a steady, uniform manner. Don’t go back over areas that are already stained. Unlike paint, stain gets darker with each coat.
If stain drips onto the deck, smooth it with the applicator pad to avoid spotting. Once the railings are complete, stain the deck boards. Load the pad with plenty of stain, yet not so much that it drips. Start by carefully “cutting in” stain along the house. If stain drips onto the siding, promptly wipe it off using a clean cloth and mineral spirits or paint thinner.
Attach a broom handle to the applicator pad. Glide the pad along the length of the deck boards, staining with the grain (Photo 9). Stop only at the end of a board. Otherwise, the overlap where you stopped and started could be noticeable.
Once the deck is finished, apply stain to the stair treads, working your way down the stairs.
Finally, use a paintbrush or spray bottle to work stain into tight areas that the applicator pad couldn’t reach, such as lattice and crevices between balusters and the rim joist (Photo 10).
Allow the stain to dry at least 48 hours before walking on it. Feel the deck to make sure the stain is completely dry. Likewise, check the bottom of your shoes before walking back into the house.
Pressure Washer Safety
- Wear appropriate safety gear and clothes. Rubber boots and gloves will protect your hands and feet. Safety goggles will keep the chemicals from splashing into your eyes, and a disposable respirator or dust mask will filter fumes.
- Keep the exhaust from the pressure washer at least 3 ft. away from any objects, including your house.
- Practice spraying the water until you find an appropriate power setting.
- Never point the wand at anything you don’t want to spray.
- Cover electrical outlets.
Choosing the Best Stain
You have two basic deck stain choices: oil-based and water-based. Oil stains are easier to apply, penetrate the wood grain and require less work when you reapply them. However, they only last two to four years.
Water-based (latex) stains last four to six years, but they’ll eventually peel and require more prep work before recoating. Opaque latex stains generally last longer than semitransparent versions. When possible, test the stain on an inconspicuous section of the decking. We used a cedar color that worked well since the wood was pressure treated and somewhat dark in color. For a darker color, a redwood-colored stain is available, while a honey color is an option for a lighter, natural wood look.
Be careful not to choose a light color stain if your deck was previously covered with a dark stain or is pressure treated (green). The light stain will not cover the dark wood or darker stain, and it will turn gray within a few weeks. If you want a natural gray or silver deck, use a clear finish. It will protect the deck from mildew and algae, but not from the sun, allowing the deck to start graying in a month or two.
The following companies offer a full line of products for power washing and finishing your deck, including strippers, brighteners and stains. The products are widely available at home centers, hardware stores and paint stores. Each company’s Web site features a store locator to find the company’s products.