How To Get Rid Of Black Mold On Wood Deck

Black mold on your deck isn’t just unsightly; it can damage your deck and adversely impact the health of those using it. When inhaled, black mold spores can cause respiratory problems, while wood-eating fungus can cause rot and decay, laying waste to a deck.

With that in mind, it’s essential to remove black mold as quickly as possible. Before opening up your wallet to pay for an expensive professional cleaning, consider ridding your deck of that black mold yourself with common household cleaners you probably already have in your home.

To remove black mold from deck wood, apply a solution of ordinary dish soap and water to the deck, scrub it with a scrub brush attached to a pole, spray it clean with a hose, then spray the deck with vinegar to prevent new mold growth.

In this article, we’ll examine this and other methods for safely removing black mold from your deck without harming your health, landscaping, or the deck wood.

Black Mold On Wood Deck

What Is Black Mold?

Black mold, or Stachybotrys chartarum, is a micro fungus that grows on material with high cellulose content, including fiberboard, gypsum board, and lumber. Because black mold requires a significant amount of water to grow, it generally exists in places that are always wet.

In addition to being unsightly, black mold can cause serious respiratory problems, which is why it typically requires professionals to perform mold removal or mitigation when found on a home’s interior.

Why Is Black Mold Growing on My Deck?

Black mold is most common in hot and humid climates where the deck wood is often moist. If the wood in these climates isn’t adequately treated with sealer and regularly cleaned, black mold will eventually grow on the boards.

Black mold is also common with decks in wooded areas that see little direct sunlight. Shaded decks take longer to dry out after the rain, making them more susceptible to black mold growth.

There are a variety of reasons why black mold might be taking up residence on your deck.

Over-applying deck stain is one common cause. Too thick a layer of deck stain can increase a 24-hour drying time to several days, giving contaminants such as tree pollen and dirt to end up in the stain. Once trapped in the stain, these contaminants can breed mold, resulting in black mold growth.

Certain oil-based stains can also cause mold growth. Oil-based stains have additives that can promote the growth of molds. For this reason, most oil-based stains include algaecides to prevent this from happening. Cheaper stains that don’t have an algaecide can promote black mold growth on a deck.

While water-based stains may not have chemicals that promote mold growth, they aren’t as durable as oil-based stains and can cause black mold to grow as the stain wears and fails.

Is Black Mold Dangerous?

Black mold can cause serious respiratory and even pulmonary health problems in people and pets, which is why most homes are inspected for mold before being sold.

Health concerns associated with black mold are more of an issue when black mold forms inside homes where the mold spores become concentrated in the air and can more easily be inhaled by residents.

While this isn’t as big of a concern outdoors where there is ample ventilation, it still presents a health hazard. In addition to spewing mold spores into the air, black mold can also make a deck very slick, making it dangerous to walk on. This is especially hazardous if the black mold is allowed to grow on deck stairs.

Can Black Mold Damage My Deck?

Black mold isn’t just unsightly. If left unchecked, it can and will eventually destroy a deck as black mold is usually accompanied by wood-eating fungus.

Mold breaks down the wood fiber, leading to rot and decay. Rot will ultimately impact the structural integrity of the deck, requiring parts of the deck to be replaced.

What Kills Black Mold on Wood

When it comes to removing black mold from a deck, there are a variety of options. Laundry detergent mixed with water is an effective way to remove mold. The detergent kills the mold to the root and is generally easy on the environment.

While some people will use bleach, it has a harder time penetrating the wood, which could leave the mold roots intact, allowing them to regrow. Bleach is also very harmful to the environment and may damage the wood fibers on the decking.

A pressure washer, when used properly, is an excellent way to remove the black mold while brightening the wood and returning it to its former glory. However, care must be taken when using a pressure washer to prevent damaging the deck.

How to Remove Black Mold From Wood Deck

How to remove black mold from wood deck

There are numerous options to consider when determining how to best remove black mold from a deck. In the next section, we’ll review some of the best methods for black mold removal.

Common Household Items

Cleaning black mold from a deck doesn’t have to involve the purchase of expensive deck cleaners or an expensive pressure washer rental. Simple laundry detergent, white vinegar, or oxygen bleach are all cleaners most people already have at home that can be used to effectively remove black mold from a deck.

For laundry detergent, mix about 1/3 of a cup of detergent with water to create a cleaning solution. Use a large brush to scrub the deck with the solution. The detergent will quickly kill black mold while also setting up a shield to prevent new mold from growing.

A vinegar and water or a baking soda and water solution used as a spray in tandem with a soft bristle brush for scrubbing the solution into the deck are also effective.

While chlorine bleach is not recommended because it will damage the deck, an oxygen bleach spray will kill mold without affecting the wood, making it a good option.

The biggest positive of using these household items is they are generally easier on the environment. This also means they are less likely to kill any grass or landscaping you have around the deck that may be affected when the cleaner is rinsed off the deck.

That said, if household cleansers may not be enough to handle advanced mold growth problems that require a more powerful cleaner.

Trisodium Phosphate

TSP, also known as trisodium phosphate, is a powdered cleaner that is particularly effective at killing mold and mildew, including black mold. TSP is an industrial cleaner, so make sure to have protective gloves and eyewear to avoid injury when working with it. TSP works on a ratio of 1.5 cups to every two gallons of water.

Apply the solution, then use a scrub brush attached to a pole to scrub the cleaner into the deck. For particularly stubborn mold, add oxygen bleach to the mixture. When done, hose off the cleaner. While TSP offers an effective means for cleaning decks with advanced mold growth, keep in mind that it is harmful to the environment and your landscaping, so use wisely and sparingly.

Chemical Deck Cleaners

Removing mold from deckChemical deck cleaners provide some of the most convenient means for cleaning a deck. These products are specially formulated with the right ingredients for killing black mold and often include a sprayer that makes application easy. Look for a cleaner that contains a mildewcide and will kill black mold to the root.

A good mildewcide will also leave a protective barrier that prevents the return of any mold. While mildewcides are some of the most effective means for killing existing black mold and controlling the growth of new black mold, they can also be costly compared to cleaning products you may already have at home.

Pressure Washer

Remove mildew from deckA pressure washer is one of the fastest ways to rid your deck of its mold problems. These powerful tools can produce a spray of water at around 2,000 psi or more, creating enough force to blast the mold from the wood. A pressure washer also works quickly. What takes hours of scrubbing with a cleaner might only take minutes with a good pressure washer.

Just keep in mind that a pressure washer works to remove mold from the surface. To kill the roots of the mold to prevent it from returning, mildewcide should be added to the sprayer to kill the mold to the root.

Before using a pressure washer, assess the situation. If there is a significant build-up of black mold and other grime, you’ll need to begin by applying cleaner to the deck first using a pressure washer tip designed for dispensing soap. After the soap is applied, scrub the deck using a long handle scrub brush,

Using a wide-angle 40 to 60-degree nozzle, spray the deck from about 2 feet away using a sweeping motion. Do not use a nozzle with a narrower tip or spray too close to the wood, or the pressure may end up damaging the deck.

For softer woods, such as pine and cedar, use a low psi of between 500 and 600. Hard, harder woods can safely withstand up to 1,500 psi.

How to Remove Mold From Stained or Painted Wood

Although mold grows most easily on bare wood, old stain or paint that is beginning to fail can allow black mold to take root and grow. To clean mold from a stained or painted wood surface, use regular household dishwashing detergent and warm water.

Three or four tablespoons per gallon are enough to do the trick. Apply the solution and scrub until clean. Avoid using bleach to clean stained or painted wood as it can cause discoloration.

A pressure washer isn’t a good option with painted decks as the pressure washer can easily strip the paint. Once the area is clean, apply vinegar to kill any black mold roots and as a preventative to stop new mold growth.

How to Remove Mold From Composite Decking

Care needs to be taken when using cleaning products with composite wood to avoid damaging the deck. Pressure washers should never be used on composite decking as the force of the water can easily “imprint” the plastic in the decking, ruining it.

It’s also a bad idea to use bleach on decking. Most composite decking manufacturers warn that bleach will discolor their products, especially if used in sunlight. Chlorine bleach can also affect the composition of the decking, causing it to crack or chip prematurely.

Instead, use a mix of dishwashing liquid and water, which will remove the mold but is mild enough not to harm the deck. As with cleaning stained and painted decking, apply vinegar with a spray bottle after cleaning to prevent future mold growth.

How to Prevent Mold on a Deck

As with many things in life, an ounce of prevention is worth a pound of cure. The best remedy for a black mold problem on a deck is to prevent it from happening in the first place.

Since black mold thrives in wet conditions, the best way to prevent it from growing is by keeping the deck dry. Ideally, your deck would get a good dose of direct sunlight each day, drying the deck quickly, keeping mold at bay.

If you have awnings or other coverings over the deck, consider removing them or rolling them back to allow the deck to dry. While sunlight is an ideal preventative for black mold, most homeowners have little control over how much sunlight the deck receives.

When there isn’t enough sunlight to keep the deck dry, treat the deck with a water sealant once a year. This will prevent the wood from soaking up the moisture, allowing the deck to dry faster after rain.

As we discussed above, it’s also important to be mindful when staining a deck. Make sure to use a quality stain that dries quickly and includes herbicide additives. This will prevent impurities such as dirt and pollen from becoming stuck between the stain and the wood, where they can breed mold.

It’s also crucial to keep debris off the deck. Clumps of fallen leaves, pollen, and sticks are sources of food for mold, promoting its growth. Prevent debris from building up on the deck and clean the deck a few times a year to eliminate any spores or food sources that make their way onto the deck surface.

How to Get Rid of Mold Under a Deck

Black mold that forms on the underside can be unsightly, especially if you have a two-tiered deck and you’re forced to look at it every time you use the lower section.

Removing this mold can be a real challenge, requiring ladders and difficult above-the-head work.

A pressure washer is the most effective way of cleaning the underside of a deck; however, it can be tricky as using too much pressure will damage the wood.

Another option is to use a garden sprayer with a cleaning solution. A solution with oxygen bleach, which unlike chlorine bleach, won’t harm plants, is effective at cleaning away mold.

Apply the solution, use a scrub brush on the end of the pole to remove the mold, then use a standard garden hose to rinse.

Keep in mind that cleaning the underside of a deck presents additional hazards. Working from a ladder presents the danger of falling, and cleaning the underside of the deck means water and cleaning agents will be dripping onto you as you work.

With that in mind, be sure to use protective goggles and clothing when cleaning the underside of a deck, as you will get wet.


The most affordable and effective way to clean a deck without harming the deck itself is to use a solution of warm water and mild dishwashing soap with a wide scrub brush attached to the end of a pole.

This will remove the mold while protecting the deck from potential damage. And, it won’t cost you much money, especially if you already have the brush and soap.

For decks with more advanced mold issues, pressure washers and powerful industrial cleaning agents like TSP are good solutions.

Whether working with dish soap or trisodium phosphate, it’s important to keep safety in mind. Rubber gloves, protective eyewear, and clothing that will protect the skin are all good precautions to have when working with cleaning products.

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