How to Clean a Composite Deck 

 August 9, 2021

By  Dale Keese

A composite deck is made of composite lumber as opposed to just wood. Composite lumber is a combination of wood fiber, plastic, and a binding agent. It is denser and stronger than wood, which makes it ideal for outdoor usage. In recent years, composite decks have gained in popularity because it has greater stain and mold resistance than wood and it can withstand more wear and tear, which, overall, equals to a longer lifespan. 

Wood Pile

Naturally, composite lumber is more expensive than wood, but it is low maintenance too. In the long run, a composite deck will help you save money. Capped composite lumber, with a thin protective veneer or cap on top of the composite surface, provides even greater protection against stains, scratches, and wear and tear.

However, composite lumber is not completely immune. Cleaning must be done on a regular basis. When it comes to cleaning your composite deck, there are three parts to it:

  1. 1
    Firstly, even though composite lumber has superior stain resistance, sealing your composite deck is important and you should still clean up spills immediately and remove any existing stains right away.
  2. 2
    Secondly, composite wood decks should be routinely swept or vacuumed and washed.
  3. 3
    Finally, you should put in place certain maintenance measures to ensure that you have a clean composite deck all year long.

Spills and stains should be cleaned using an appropriate cleaner for composite wood within a week at most. The longer you allow the stain to remain on the composite deck’s surface, the more difficult it will be to clean and remove it. This is the key to extending it's life.

Stain-producing substances stuck in the embossing patterns on the deck will be the hardest to remove if you do not clean them right away.

Oily Stains

When it comes to cleaning oily stains, you will need a mild, non-acidic, and preferably pH-neutral liquid soap; a soft bristle brush; one bucket of lukewarm water; and one bucket of warm water. You can use a degreasing product as a cleaner as well. Mix a teaspoon of soap in lukewarm water, then dip the brush in the cleaning solution and scrub the stained area with it.

Once the stain has been removed, wash and rinse the area with warm water. The mild soap might not work on oily stains that have been sitting on the deck for over a week or if the stain is particularly stubborn. In such cases, replace the mild soap with a de-greaser or a specialist commercial oil stain cleaner in the cleaning solution discussed earlier.

Dirty Wood

Water Spots or Tannin Stains

Water spots or tannin stains regularly occur on wooden decks. The pure form of tannin is a natural vegetable dye that you can usually get from bark and plants. Other common tannin stains are from beverages that contain tannin like fruit juices, tea, wine, and coffee. While composite decks do resist these stains better than their wooden counterparts, over a period of time, you will notice water spots.

To clean water spots or tanning stains, first, you will have to sweep or vacuum the deck to remove all dirt and debris from it. Once that is done, apply a deck brightener with oxalic acid. Make sure that the deck is completely dry by the time you apply the brightener. The instructions for applying the brightener will be mentioned on the bottle or container. Composite lumber manufacturers recommend specific brighteners for their decks. So, you should adhere to that.

Note that the brighteners can also be used to clean and remove rust stains and stains that are particularly stubborn. Apply the deck brightener with a brush on the stained area and let it sit for 15 to 20 minutes. Use a regular garden hose to wash and rinse the spot after that.

Routine Cleaning

Routine cleaning is an essential part of composite lumber maintenance. Regularly cleaning composite decking will not only ensure that stains do not settle on the composite deck but will also increase its lifespan.

Sweep or Vacuum

You should sweep or vacuum the decking at least once a week to get rid of all dirt and debris. The frequency will depend on how much traffic the deck gets every day and season. Muddy patches are more likely to be an issue during monsoon season, while dead and dried leaves during winter. In such cases, you will have to sweep or vacuum the floor two to three times a week.

When it comes to vacuuming and cleaning composite decks, use the crevice tool provided with the vacuum cleaner to loosen dirt and debris stuck in between the boards and in the patterns if any. A leaf blower does a good job of blowing away dirt and debris as well.


For dirt and grime that is stuck to the surface, you will have to scrub it clean with a composite deck cleaner. First, use a garden hose to thoroughly wash the surface and loosen the dirt and grime. Use a high-powered nozzle on the hose. Then, mix a few drops of liquid dishwashing soap in a bucket of warm water, dip a soft bristle brush in this cleaning solution, and scrub the deck with it.

When cleaning a composite deck, pay extra attention to the crevices and embossing patterns because the most stubborn dirt makes these spaces their home. Remember to not use a stiff brush because that might scratch the surface and damage the veneer. Typically, scrubbing the deck a couple of times in a year is good enough, but if the manufacturer recommends that you do it more frequently, then adhere to that.

Vacuuming Floors

Power Washing

Power washing or pressure washing a composite deck is an alternative to scrubbing. Any one who's done some cleaning in the past can say that scrubbing is, without a doubt, more effective, but it takes up a lot of time and requires a lot of effort on your part. Whereas, power washing is faster and easier. Those who have really large decks prefer this cleaning method over scrubbing.

Before the power washing can begin, you need to sweep clean the deck and clear as much dirt and debris as possible. Next, test the power washer in one corner to check if it damages the surface in any way or not. This is especially important the first time you use a power washer. If the test result is positive, then go ahead and apply a composite deck cleaner solution across the deck.

The cleaning solution can be a liquid dishwashing soap mixed with warm water or a commercial de-greaser or a stain remover. Allow the composite deck cleaner to sit for a period of time. This period will be the amount of time recommended by the manufacturer. Finally, switch on the power washer and thoroughly wash the deck. It will take at least 24 hours to dry out completely.

There are a few things you need to keep in mind while using a power washer.

  • Read your power washers instruction manual. If you are renting it, then ask the supplier to demonstrate how to use it.
  • Ideally, rent a power washer that has a built-in cleaning solution dispenser. It will make your job easier.
  • Read the composite manufacturer’s instructions regarding the level of pressure to use and the type of nozzle to use on the power washer.
  • Always spray in the direction of the composite grain.
  • Never direct the sprayer towards yourself or anyone else.
  • Make sure there is no one nearby while you are power washing. Tiny debris and other particles fly off the deck and can injure the person.

Maintaining the Deck

Composite lumber should be kept dry as much as possible. A properly functioning drainage system around the deck can help you achieve that. If moisture is allowed to sit for too long, it can result in mold formation. To prevent this, there must be adequate drainage around the deck and in between individual planks.

While installing a composite deck, make sure there are at least 6 to 8 inches between the lumber and the ground beneath. This creates enough ventilation space and helps keep the surface dry.

Any water on the surface will drain off into the ground and the lumber will not be in contact with the wet ground either. In order for the water to drain off, you also need to make sure that the gaps between individual planks is free of dirt and debris. If the gaps are blocked, the water will remain sitting on the deck.


You should consider applying a sealant to your composite deck to give it further protection. It will also help if you need to remove ice and snow. You can use rock salt to melt the snow and the drainage system will take care of the rest or you can use a plastic shovel to remove it.

Outdoor Lighting

If you do use rock salt or if you live close to a saltwater body, then get the structure checked by an expert to determine its safety. Excessive salt can cause corrosion over time.

One other thing you need to keep in mind is not to use any harsh cleaners such as chlorine bleach or ammonia as composite deck cleaners. Certain dishwashing soaps contain ammonia. So, be careful of using them as well.

You're now an expert in cleaning composite decks properly with the right cleaner, you can be assured that your deck will be looking great all year long.

About the author

Hey, I'm Dale Keese.. thanks for reading.. hopefully this article can save you some time and trouble with your sealing job. I'm also in the process of making some video walk-throughs for youtube so check back soon! thanks

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