Pressure Washing Decks

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A beautiful wooden deck, properly maintained, can add greatly to the aesthetic and resale values of a home.

Just look around, decks are almost everywhere. Not just houses but both municipal and commercial facilities use wooden decks and walkways extensively. Because of this pressure washing decks can be a great profit center for your business or even the whole business.

The great news is that decks need maintenance. As beautiful as a wooden deck can be it can be a real eyesore if not properly maintained.

Why Decks Need Maintenance

When a wood deck absorbs water the natural resins and color can be washed out over time.

The combination of wood and water creates a food source for mildew, fungus and mold promoting their growth. Wood and water combined with dirt and even air pollutiom will also contribute to the proliferation of mildew, fungus and molds. One thing to remember is that a wet deck with a thick coating of mildrew is very slick and slippery. This creates one heck of a "slip and fall" liability problem. Keep this in mind when speaking to the decision makers of commercial and municipal facilities.

Learning Curve

There is a learning curve involved when getting proficient enough to clean/seal/restore wood decks for the public. It is best to learn on your own deck or on the decks of close friends and relatives. When learning make sure to do more than one. Different decks can present different challenges.


When organizing your project or preparing your bid make some simple observations.

Has the deck ever been sealed? Is there old sealer that needs to be stripped and reapplied?

Do I have all the chemicals, tools and equipment required for this project?

( we will include a sample list at the end of this article)

Is there any damaged or rotted wood that needs to be replaced?

( Now is a good time to measure.)

Are the any missing or loose bolts, nails or screws?

Are there any adjacent bushes or plants that need to be protected?

Are there any electrical appliances, outlets, light fixtures or telephone jacks?

Note: these will have to be sealed water tight. Remember water and electricity is a dangerous combination. Decks in upscale neighborhoods will probably contain most of these challenges. Make sure the circuit breakers will be accessible to you prior to starting.


Ok you've cleared everything from the deck and placed it far enough to be out of harms way. You've locked out the circuit breakers that provide electrical service to the deck area. Outlets, fixtures and jacks have been sealed water tight.

Close proximity plants and bushes have been protected with a clear plastic tarp.

Loose bolts. nails and screws have been tightened or replaced.with galvanized fasteners.

Rotted or damaged wood has been replaced.

Only now are you really ready to begin.

Clear the Deck of Dirt and Debris

With a stiff bristle broom or a leaf blower clear all loose dirt and debris from the surface of the deck..

What Chemicals to Use

Sodium Hydroxide ( a high caustic chemical) is very popular with professional deck cleaners. Because this chemical does most of the work very low pressures of 500-1200 PSI can be used which helps avoid the condition known as "furring".

Safety note: Always wear headgear with face shields and cartridge type respirators when working with high caustic or acidic chemicals. This is not a suggestion it's a must.

While Sodium Hydroxide is a very effective chemical it will darken or may even blacken the deck. Because of this the PH will have to be nuetralized with a mild acidic solution. Acids used are Citrus,Oxalic or Phosphoric.

These acid solutions will act as brighteners. Neutralizing the PH of a high caustic cleaner will restore a deck very close to it's original color.

Add approx. 5oz. acid to each gallon of water.

Citrus Acid- Used on hardwoods.

Oxalic Acid- Primarily used on redwoods.

Phosphoric Acid- Used when an unfinished deck has turned "gray".

I'm very hesitant to suggest a pressure level when it comes to cleaning decks because it's just so subjective. One deck will have harder wood than another and

other decks will have softer and harder areas on the same deck. In this respect only experience can really guide you. As a general rule of thumb use the least amount of pressure that will get the job done.

Test pressure on an inconspicuous area of the deck. The underside works well for this

Excessive Pressure.

Excessive pressure will cause a deck to "furr".This is the appearance of small hairlike fibers protruding from the wood.. Your customers will not like the way this looks and light sanding will be required to correct this condition.

Ready, Set, Go!

Soak the area to be cleaned thoroughly. This serves several purposes but most importantly, the deck must remain damp throughout the entire cleaning process.

Apply cleaning chemical with the applicator of your choice.When just starting out a pump up type sprayer will work nicely. Allow your chemical to dwell for 15-20 minutes. Do not allow to dry. If necessary spray more water or reapply chemical.

If you've sufficiently dampened the deck and haven't dawdled this shouldn't be a big problem.

Clean. Remember when cleaning use low pressure. Never clean against the grain or accross the grain. Feather each pass. The pressure used should be enough to remove dead wood but not enough to cause "furring" Experience will be your best teacher.

Rinse deck thoroughly removing all chemical. Apply nuetralizer/brightener solution, wait 10-15 minutes and rinse well again.

If you are going to seal wait 24 hours if not 48. If you chose your day well rain won't become a problem.

"Furring" Happens.

Sometimes "furring will become apparent even at low pressures. These short hair like fibers are the result of a "tearing" action on the wood. These will probably be gone in 2-3 weeks but your customer will want them gone sooner than later. Give them a light sanding with a bronze metal scrubbing pad. Use bronze, steel wool can leave rust stains.

What not to leave behind

Here is a general list of things to bring to your job site. Some of this may not apply to you. The point is to always work with a job list to avoid the embarrasment or expense of missing that tool you need right now.

Pressure Washer- Cold water gas machine 5.5-11HP commercial grade unit.

(Hot Washers are also used but at very low temperatures not exceeding 110F)

Hoses- Sufficient lengths of both pressure hose and supply hose.

Brooms/Blower- A stiff bristled push broom (not metal) and/or a gas powered leaf blower.

Chemical applicator - Pump-up type sprayer or Flo-Jet type sprayer

Mixing Buckets - 2or3 5 gallon plastic mixing buckets.

Mixers- Drill type chemical mixer.

Respirator- Cartridge type with spares

(When working with high caustics and acids)

Face and Eye Protection- Some type of helmet with face shield.

Cordless Drill- With phillips screwbit and chuck large enough to accomodate chemical mixer.

Hammer- If nails are required.

Deck Screws, Nails and Bolts- As required, use galvanized only.

Duct tape, Clear plastic sheeting,Cardboard- To protect areas

Extension Cords- Must be adequate length and gauge. 12 gauge minimum.

Electric Rotary Sander- With 60 and 80 grit sandpaper

Knee Pads - You didn't think you'd always be standing when sanding did you?

Remember practice makes perfect get out there and start learning.

About the Author

Randall Madon is the founder and president of ATT Pressure Supply along with a new educational resource site: - Learn More.

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