How to Clean a Composite Deck

  • September 21, 2019
  • / By Dale Keese
Wood Pile

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’s denser and stronger than wood, which makes it ideal for outdoor usage such as in a deck. 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 all equals to a longer lifespan. 

Wood Pile

Naturally, composite lumber is more expensive than wood, but it’s 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 decks aren’t completely immune. So, it needs to be taken care of and cleaned on a regular basis. When we talk about how to clean your composite deck, there are three parts to it.

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

Spills and stains should be cleaned within a week at most. The longer you allow the stain to remain on the composite deck surface, the more difficult it will be to remove it. This is the key when you’re considering cleaning your composite deck. Stain producing substances stuck in the embossing patterns on the deck will be the hardest to remove, if not dealt with right away.

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 de-greasing product as well. Mix a teaspoon of soap in the lukewarm water, then dip the brush in the solution and scrub the stained area with it.

Once the stain has been removed, 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.

Dirty Wood

Water Spots or Tannin Stains

Water spots or tannin stains regularly occur on wooden decks. While composite decks do resist these stains better than wooden decks, over a period of time you will notice water spots.

First, you will have to sweep or vacuum the deck to remove all dirt and debris from it. Once that’s done, apply a deck brightener with oxalic acid in it to the deck. Make sure that the deck is completely dry at the time you apply the deck brightener. The instructions for applying the deck brightener will be mentioned on the bottle or container. Composite deck manufacturers recommend specific deck brighteners for their decks. So, you should adhere to that.

Note that deck brighteners can also be used to 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 rinse the spot after that.

Routine Cleaning

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

Sweep or Vacuum

You should sweep or vacuum the deck 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. There’s a greater chance of muddy patches during monsoon and dried, dead leaves during winter. In such cases, you will have to sweep or vacuum the floor 2 to 3 times a week.

Use the crevice tool provided with the vacuum cleaner to loosen dirt and debris stuck in between the boards and in the patterns on the deck if any. A leaf blower does a good job of blowing away dirt and debris on the deck as well.


For dirt and grime that’s stuck to the deck surface, you will have to scrub. Firstly, use a garden hose to thoroughly hose the deck 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 soapy solution and scrub the deck with it.

Pay extra attention to the crevices and embossing patterns, because the most obstinate dirt makes these spaces their home. Remember to not use a stiff brush, because that might scratch the deck 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. 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 method over scrubbing.

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

The cleaning solution can be a liquid dishwashing soap mix with warm water or a commercial de-greaser or a stain remover. Allow the cleaning solution to sit on the deck 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. The deck will need 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 the instructions on how to use a power washer. If you’re 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’s 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 decks should be kept dry at all times. A properly functioning drainage system around the deck can help you achieve that. If moisture is allowed to sit on the deck for too long, it can result in mold formation. To prevent this there must be adequate drainage around the deck and in between individual deck planks.

While installing a composite deck make sure there are at least 6 to 8 inches between the deck and the ground beneath. This is an important part cleaning your composite deck. This creates enough ventilation space and helps keep the deck dry.

Any water on the deck surface will drain off into the ground and the deck 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 deck planks in 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 off the deck. 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 on composite decks. Certain dishwashing soaps contain ammonia. So, be careful of that as well.