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How to Pressure Wash Your Deck

July 01, 2016 by K

SIMPSON® MS31025HT 3100 PSI @ 2.5 GPM MegaShot Series Pressure Washer

Pressure washing your deck is the best way to quickly and efficiently clean all the build up that the weather leaves on the wood.  Your deck will be bright and revitalized for you to enjoy all season long!

Here we have a deck that is in need of some TLC and SIMPSON® is just the right pressure washer to do the job. Here we will show you basic set-up of your pressure washer and some tips to clean your deck by using pressure washer accessories. Accessories are a beautiful thing for pressure washers to speed up your cleaning time and also make sure you are not doing damage to the wood.

One of the main issues homeowners run into when attempting to pressure wash their deck is that they often do more harm than good. Sometimes homeowners think that more pressure is better, which often leaves deep and unsightly damage to the wood. With each new detrimental mark, people tend to add more pressure trying to erase the mistake. This will only add more damage to the wood and is not recommended! Rest assured, it does not need to be this problematic for the homeowner and here at SIMPSON® we will show you the right tools to get the job done.


It is very important to inspect the deck first.

Ask yourself these questions: Is the wood older? Is it stained or is there buildup of coating from the past? Is it a large surface or smaller with more intricate corners? These factors will help you determine the correct nozzle, cleaner and wand distance required. If there is significant buildup of stains or sealants a pressure washer safe cleaner may be required prior to pressure washing but typically, water pressure is enough to remove the buildup.

This deck is older and the wood is much softer, requiring you to use a larger fan degree nozzle. The smaller the degree, the harder it is on the wood. For most deck surfaces 1500 pounds per square inch (PSI) is more than sufficient.

UNDERSTAND: pressure (PSI) will blast the dirt loose and the flow rinses the debris away. We recommend that you use a 25-degree nozzle (for more stubborn build-up) to 40-degree (for newer decks with less damage or synthetic wood). We do not like to use any smaller degree nozzle than 25 degrees unless needed for EXTRA tough spots – However, this may damage your wood so be sure to test a small area with the chosen tip before beginning a larger area to ensure it does not cause any visible damage to the surface. We will also demonstrate how accessories can be of much help while cleaning below.

MAIN GOAL: clean away dirt and debris but leave no visible traces in the wood or leave raised wood fibers.

Always, prior to starting, make sure to have on the appropriate safety gear. These machines are very powerful and the force can lead to injury. We recommend a closed-toe boot/shoe (steel toe and water resistant is great!) Also, eye protection from any debris that may fly your way.

ALWAYS read your user manual before starting!


Today we are using the MS31025HT MegaShot Series pressure washer. This is a 3100 PSI (pressure) @ 2.5 GPM (flow.) Equipped with a HONDA® engine and OEM Technologies™ pump. Includes our 25′ MorFlex™ hose for extra flexibility, kink resistance, and won’t leave scuff marks. (For extra length and leverage for your MorFlex™ hose you can also purchase an extension hose that comes in 25′ or 50′. This unit also includes 5 nozzle tips for a variety of cleaning: 0, 15, 25, 40 and soap.

Prior to starting, make sure you remove any furniture or delicate items from your decks surface.

Here are a few accessories that you can purchase along with your machine, and in our professional opinion, is a MUST HAVE!

SIMPSON Turbo Nozzle is a powerful oscillating nozzle that removes extra tough spots and is perfect for second story decks (underneath where it is hard to clean.)

SIMPSON Dial-N-Wash® is amazing for adjusting your pressure right at the wand so that you do not need to switch nozzles for different areas that require more or less pressure.

SIMPSON Surface Scrubber will clean large areas on flat surfaces saving you TONS of time as opposed to using a regular nozzle.

Now lets start with basic set-up:

Connect High Pressure Hose to Outlet

Connect your MorFlex™ hose to your machine outlet by twisting clock-wise until secured.

Connect High Pressure Hose to Gun

Connect the other end of your hose to the gun by twisting clock-wise again until secured.

Connect Garden Hose to Water Inlet

Connect your garden hose to your pressure washer inlet and twist the connection clock-wise to make sure it is tightly secured.  You don’t want any leakage while pressure washing if this connection is loose. Then, turn on your water supply.

Pull Trigger to Ensure Water Flow

Make sure you have a solid flow of water coming through the machine by pressing the gun trigger. If you do not have a solid flow then you will want to inspect your water supply prior to starting the machine.

Pull Back QC

Insert Nozzle Tip

Insert your choice of nozzle by pulling the quick coupler back and inserting your nozzle. Once the nozzle is inserted release the quick coupler and make sure the nozzle is secure. If your nozzle is not secure it will blow off once you pull the trigger and this could potentially be dangerous. Today we are using the SIMPSON Turbo nozzle since we are going to start with the top of the upper deck awning. This can sometimes be hard to reach with a typical nozzle and by using a turbo nozzle it will allow us to achieve that extra force we will need to clean.

Check Oil

Switch to ON Position

Pull Choke

Now you will want to make sure you have a full tank of gas. Always be sure you are using ethanol free gas or 10% ethanol or less as ethanol can ruin your engine.

Your SIMPSON machine will come with a bottle of oil in the box, but always be sure before each use that your oil tank is full with the appropriate amount of oil. Reference your user manual for the correct amount of oil for your machine.

Turn your engine on by flipping the on/off switch to ON.

Pull your choke (especially if the machine has not been started for a while.) After your machine is started you will push your chock back inward.

Start Engine

Pull your engine cord by pulling straight out until engine starts.  If your engine cord seems stuck or unable to be pulled simply squeeze your gun trigger to relieve pressure, then try again…that should do the trick!

Starting your cleaning job:


Start from the TOP inside corner and work your way out and down. ALWAYS clean WITH the wood grain and not against it. Make sure you do not get too close to the wood, as this can damage the wood. You will see a huge difference right away. Just Look at that bright revitalized wood!

REMINDER: If there are some spots that seem to be stubborn, make sure not to go over and over it. This will just damage the wood and you will end up in an uglier spot than you started with. You may need some pressure washer safe cleaner to remove those darker areas prior to wash to lift some of those stains left by weather damage or years of stain build-up.

You may also be interested in purchasing an extension wand if the deck awning is very high. This will give you more length and you will not have to struggle lifting your arms for hours to clean. Our Extension Wands come in 16″ and 31″.


Once the top is finished then you can work your way down. You can also switch your nozzle tip to a 25 or 40 degree as to not damage the wood with a powerful turbo nozzle. IF you are going to use the turbo nozzle on the lower parts of the deck make sure you go slow and do not get too close to the wood.  If you go to fast you may have some circle looking marks (this is caused by the oscillating effect of the turbo nozzle.) Above you can see a huge difference pressure washing makes, as the post to the right is freshly pressure washed and the post to the left is not.


Once finished with the top of your deck, you can begin to clean the bottom. We recommend using our 15″ surface scrubber that allows you to cut cleaning time in half. This is made out of steel and has two powerful rotating jets for a thorough clean that is easy to use, streak-free and no splash back.  Once you are finished with your surface scrubber you will want to use your 40 degree nozzle or Turbo nozzle to lightly blow away any of the residual mud left behind.  This will come off easily and you should not have to apply any additional pressure to the wood.

NOTE: When choosing a pressure washer accessory always be sure to buy the correct PSI for your machine. Here we used “Up to 3400 PSI” rating since our machine is 3100 PSI. Never purchase an accessory that is not within your machines pressure range or you will loose pressure or damage your accessory.


Now you are free to paint, stain, or coat your deck once dried!


-SIMPSON Cleaning Team

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