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Six Easy Steps to Pressure Cleaning Your Wood Deck Without Damaging it

Here you’ll learn why pressure cleaning your wood deck is smart, and how to do it without damaging it. We’ll look at what equipment to use, how to use it and how to future-proof your deck.

How to Pressure Clean Your Deck

With a Pressure Washer

According to the National Association of Home Builders, 25% of all US homes built between 1995 and 2005 had decks.

If you include wood porches – the number spikes to 75%…

…And, according to Consumer Reports research, your deck is a top 3 value adding feature when it comes time to sell.

So it makes sense to invest in maintaining your deck – cleaning is maintenance 101.

It will remove environmental pollutants like mold, mildew & algae and clean any hamburger grease or Coca-Cola spill stains. (Not to mention make it shine like Mother Nature intended.)

Here’s the 6 steps for max results with minimal time, effort and cash.

1. Picking the Correct Pressure Cleaner

Cleaning Back Deck

Results

With the correct pressure washer you’re results will look the good half of this:

With the wrong pressure cleaner you could damage the wood – partially ruing your deck’s future value.

Things to consider:

  • Rent or buy the pressure washer?
  • Electric of gas powered?
  • What pressure (pounds per square inch: PSI) should it be?
  • What flow rate (gallons per minute: GPM)?
  • Hot or cold water?

To buy or rent?

Verdict: Buy

You can buy a pressure cleaner for your deck cleaning for less than $150. It’ll cost at least $50 to rent one for 4 hours.

And you could use the washer you bought for your car, your boat and other cleaning jobs around your home. And you’ll probably want to wash your deck with it once every 2 years or so.

It’s really a budget thing. It may cost a bit more to buy one outright – but it’s probably worth it in the long run.

Electric or gas?

Verdict: Medium-duty electric

Electric units are more affordable but less powerful than gas. They’re also limited in range by their electric cord. Generally though you don’t need the gas power for a deck.

You’ll be able to use either (as long as you use the correct nozzle and technique) to clean your deck.

So if you’re renting it doesn’t matter. If you’re buying only to use for small jobs then get electric. Get gas if you want to use it for more than just your deck.

What PSI?

Verdict: Any residential pressure cleaner will do.

With wood you want to be careful. Too much pressure and you’ll damage it.

With the right nozzle and technique the rated PSI of the washer doesn’t matter.

An example: Using a pressure washer is intuitive. You’ll naturally move closer to the surface with the wand as you judge more pressure is needed. A 1,500 PSI pressure washer focused on 1 square inch of wood equals 1,500 pounds – easily enough to damage the wood. But, with a 40 degree nozzle 1 metre away from the deck is only 52.5 pounds (same as a garden hose). This works because the nozzle now spread the same PSI over 28.7 square inches.

What GPM?

Verdict: 1.5 to 2.3 GPM

Light-duty and medium-duty washer are the ones you’ll want to clean your deck. Their GPM range is 1.5 GPM to 2.3 GPM.

Hot or cold?

Verdict: Cold water

You should use cold water for wood surfaces. Hot water will expand the wood trapping any detergents etc.

2. Using the Correct Nozzle

Verdict: 40 degree nozzle

Briggs and Stratton 6177 Second Story Nozzle Kit

Nozzles are named based on the width of water stream they create. The 40 degree nozzle creates the widest stream of water. From 1 metre a 40 degree nozzle will spread the water to 28.7 inches…

…Compare that with a 0 degree nozzle which will focus the entire pressure of the water on 1 inch by 1 inch of the surface.

Use a 40 degree nozzle to clean your deck. No matter what pressure cleaner you’re using test on the underside of the deck to ensure it doesn’t damage the wood.

3. Should I Use Chemicals?

Verdict: Yes

Different chemicals have different purposes. Let’s look at the most common for deck cleaning:

Bleach (Sodium Hypochlorite)

Bleach will brighten your deck and kill mold and mildew, but will not do a great job cleaning deep. Out of all the chemicals you can use bleach gives the most instant results – your deck will look clean.

Since wood’s pH is acidic and bleach is basic, you’ll need to rinse the wood with a slightly acidic solution of oxalic or citralic acid to avoid long term damage to the wood.

Caustic Cleaners (Sodium Hydroxide)

Caustic soda solutions, commonly used in detergents and drain cleaners, will be your go-to chemical for removing the sealant from a previously sealed deck.

You’ll need to neutralize after use to return the wood to its natural pH.

Caustic cleaners are the strongest cleaners used on wood decks and you would probably not even need a pressure cleaner to do more than just wash it all away. However, caustic cleaners are corrosive and will burn your skin if left untreated.

Detergents (eg: TriSodium Phosphate and water)

A detergents is a mixture of ingredients in water that work together to “loosen” dirt and grease from a surface allowing for it to be easily washed away. Detergents work best when combined with bleach because bleach is much better at killing the mold and mildew.

There are many detergents on the market for everything from cleaning your clothes to cleaning your driveway and deck. Detergents are safe and affordable and a great option for residential use.

“All-in-One” Products

These are proprietary combinations of chemicals that work to clean a specific surface. Companies can easily market these as “deck cleaner” or “driveway cleaner” to use in combination with a pressure cleaner.

They’re the best option for the DIYer. Professional will tend to use combinations of the above chemicals, but for most people these “All-in-One” products work great. Examples: Krud KutterKarcher Multi-Purpose Cleaner.

4. Preparing the Deck

  • Sealed or unsealed deck, doesn’t matter, your first step is removing everything from it – table, BBQ, flower pots etc.

Unsealed Deck Preparation

  1. Sweep or blow all dirt and leaves and other loose debris from the deck.
  2. Wet surface with garden hose.
  3. Apply detergent or all-in-one cleaner with a sprayer.
  4. Wait 10 – 15 minutes. (the hotter the day  the less time you wait).
  5. Power clean with 40 degree nozzle and medium-duty electric cleaner.
  6. Repeat in 10′ x 10′ areas until deck complete.
  7. Repeat steps 3 to 6 with a brightener (bleach).
  8. Wash down entire deck with light acidic solution to return wood to original pH.

Sealed Deck Prep

  1. Cover off surrounding painted areas and windows to ensure protected from caustic cleaners.
  2. Clean loose debris from deck.
  3. Water down deck and deck surroundings.
  4. Apply caustic cleaning solution with a sprayer.
  5. Follow steps 7 and 8 above.

Sanding After Pressure Washing Wood Deck?

The bleaches and caustic chemicals (if used) will cause the wood fibres to appear loose. You’ll want to sand the deck once dry to ensure surface is safe for barefoot walking. If you’re going to seal it after sanding make sure not to go finer than 140 grit sand paper cause the sealant won’t be able to absorb properly..

5. What’s the Correct Pressure Washing Technique?

  • Work in manageable areas to ensure the chemical doesn’t dry before getting to that part of the deck. An area 10 ft x 10 ft is good.
  • Wash with the grain not against it.
  • Adjust how high pressure wand is above deck as you go – you’ll see it working.

6. Future-Proofing Your Deck

Cleaning your deck is a great way to ensure it remains functional. Repeat the process every 2 years to ensure maximum deck health.

Since the sun and water damage the wood covering your deck with a roof can protect it. But given the cost and effort cleaning is a much better option for a back deck.

Safety Tips

  • Take 5 and Think About the “Swiss Cheese” Dangers: This exercise gets you to visualize the task to ensure things like removing trip hazards is done. Swiss cheese dangers are one’s where multiple things line up to create an unexpected but catastrophic result (multiple slices of swiss cheese line up to create a pathway through them). These are things like your cat running into the pressure water stream getting a fright and jumping up to scratch your eyes so you fall backwards off the deck. Avoid these by being aware they are possible – lock the cat inside and be sure you’re always aware of your surroundings.
  • Use Eye Protection: Always use eye protection. They’ll protect you from flying debris. Sunglasses work fine.
  • Use Hearing Protection (Gas Powered): If you use a gas powered pressure washer use hearing protection. If you’ve used a lawn mower then you know how loud a small gasoline engine can be.
  • Read Pressure Washer User Manual: Always read the User’s Manual of all the equipment you use. Tips and instruction for startup, use and shutdown will all be well laid out in the manual.
  • Read Any Chemical’s Used MSDS Sheets: Always read the MSDS sheet of chemicals used. Be sure you know what not to mix it with and what you’re supposed to do if ingested.

Sources and Useful Links

1. How to Clean Your Wood Deck. A great article by SealRX.com, a wood and concrete sealant company.

2. Deck Cleaning and Sealing. Powerwash.com produced a great article about deck cleaning with a pressure washer. Much of the article is dedicated to what detergent to use and is geared more for contractors. Regardless, a useful resource.

3. Pressure cleaning back deck image credit. Image sourced from user Motown89 on reddit.com.

4. Using a Pressure Washer to Clean a Deck. Decks.com article on proper things to consider when cleaning your wood deck.

5. Video on youtube.com was used as a starting point for researching this article. This video is produced by Lowes and is very focused on the sealing part of the deck cleaning process.

6. Characteristics of New Single Family Homes. Article from 2006 on the National Associates of Home Builders website. Page contains many useful stats on homes built in the USA between 1995 and 2005.

7. The 5 Best-and 5 Worst Home Improvement Project for The Money. Article on USnews.com that compiles stats from Consumer Reports on the future value of wooden decks for home sellers.

Disclaimer: Although much time has been spent ensuring its accuracy – this article should be thought of as no more than a starting point for your deck cleaning with a pressure washer research. PressureCleanerReviews.com claims no responsibility for any damage done to your deck, or any other property or person as a result of pressure washing your deck based on advice from this article.

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