Black Mold On a Wood Deck: How to Remove It and Prevent It

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Black Mold On a Wood Deck

A wood deck can be a beautiful addition to your home. Spending time outdoors is more fun and enjoyable when you have a nice deck for hosting friends and family. In many households, the deck is one of the most-used areas of the house during the summer months.

Although wood decks are beautiful and functional, they require some maintenance. One of the issues that you may experience is black mold on a wood deck. You may not even notice that you have mold at first, but you’re likely to notice the dark color of the deck boards.

Black mold should be dealt with for several reasons (which we’ll cover), not just for aesthetics. Of course, there are several ways to treat or kill mold, but some involve harsh chemicals. We always recommend avoiding chemical cleaners whenever possible for the safety of everyone in your home and the environment. Thankfully, there are several ways to deal with black mold without resorting to chemical cleaners, and we’ll cover them in detail here.

Related: Natural Mold Removal: 7 Safe and Non-Toxic Methods

What Is Black Mold?

Before we go into how to remove black mold, it’s important to understand what it is and where it comes from. Black mold is a type of fungus that can grow in damp, dark areas. Although there are several types of mold, Stachybotrys chartarum is the most common type of black mold. This particular type of mold produces toxins called mycotoxins, which can be harmful to humans when inhaled.

Wood decks are especially susceptible to black mold because they’re often exposed to moisture. The combination of heat and humidity creates the perfect environment for black mold to thrive. If you live in an area with high humidity or have many trees near your deck, you may be more likely to experience black mold growth.

One of the most apparent signs of black mold is the dark color of the spores. Black mold can also appear fuzzy or slimy and may have a musty smell. If you think you may have black mold on your deck, taking action quickly is essential. The longer black mold goes untreated, the more difficult it will be to remove.

Why Does Black Mold Grow On a Wood Deck?

As we mentioned, black mold often grows in damp, dark areas. Wood decks are often the perfect environment for black mold because they’re usually exposed to moisture. If your deck doesn’t have proper drainage, water can pool on the surface and create the ideal conditions for black mold to grow.

Another reason black mold may grow on your wood deck is the type of wood you’re using. Some types of wood are more susceptible to rot and decay than others. Using a softwood like cedar or pine may make your deck more likely to develop black mold. Hardwoods like teak and mahogany are less likely to experience mold growth.

Decks should be made with treated lumber, but if for some reason your deck was made with untreated lumber, it will be even more susceptible to black mold.

Why Black Mold On a Wood Deck Should Be Removed

Aside from the fact that black mold doesn’t look very good, there are several reasons why you should take action to remove it from your deck.

Health Issues Related to Black Mold

First, as we mentioned, black mold produces mycotoxins, which can be harmful when inhaled. If you have young children or pets who spend time on your deck, they may be more susceptible to the effects of these toxins.

Black mold can cause or worsen the symptoms of asthma and other respiratory conditions. Symptoms of black mold exposure include coughing, wheezing, watery eyes, and difficulty breathing.

In some cases, black mold exposure can also lead to skin irritation. If you notice any rashes or skin irritation after spending time on your deck, it’s possible that black mold is to blame.

Structural Damage

In addition, black mold can cause structural damage to your deck. As the mold grows and spreads, it can break down the wood fibers and cause rot. In extreme cases, black mold can even cause the wood to collapse. If you don’t take action to remove black mold from your deck, you may eventually have to replace the entire structure.

Risk of Injury

Another reason to remove black mold from your deck is the risk of injury. Black mold can make your deck’s surface slippery, increasing the risk of falls and other accidents. If you have black mold on your deck, it’s important to take action to remove it as soon as possible.

How to Remove Black Mold On a Wood Deck

Now that you know the dangers of black mold, you’re probably wondering how to remove it from your deck. The good news is that there are several effective methods for dealing with black mold.

One of the most important things to remember when removing black mold is to take precautions to avoid spreading the spores. Be sure to wear gloves, a mask, and protective clothing when working with mold. You may also want to put down a tarp or drop cloth to protect the area around your deck.

Once you’ve taken measures to protect yourself, you can begin working on removing the mold.

Pressure Washing

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One of the most effective ways to remove black mold is to pressure wash it away. Pressure washing will blast the mold spores off your deck and can also help kill any remaining mold cells.

If you don’t have a pressure washer, you can rent one from a local home improvement store or buy an inexpensive one. You don’t need a high-end model for cleaning your deck. Be sure to follow the instructions carefully to avoid damaging your deck.

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You can also hire a professional pressure washing company to handle the job for you, although it’s an easy DIY job if you’re willing to put in a few hours of work.

Use a nozzle that is 40-60 degrees, which will produce a wide spray. A narrow tip creates too much force and can damage the wood. Hold the wand about 2 feet above the deck boards and test it in an inconspicuous area first to ensure it doesn’t cause any damage.

You can use a pressure washer with just water or add a cleaning solution like Simple Green Oxy Solve Total Outdoor Cleaner. We recommend starting with just water, but you may need to add a cleaning solution for more significant mold issues.

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Natural Laundry Detergent

If you don’t have a pressure washer, you can remove black mold from your deck using a natural laundry detergent and water solution.

Mix one cup of detergent with two gallons of water to make the solution. You can use any type of natural laundry detergent, but we recommend using one that is non-toxic and biodegradable, like Seventh Generation.

Once you’ve mixed the solution, apply it to the affected areas with a brush or sponge and scrub away the mold. Be sure to rinse the area well when you’re finished so that all the cleaning solution is removed.

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White Vinegar

Another natural solution for removing black mold is white vinegar. Vinegar is a mild acid that can kill mold cells and prevent them from growing back.

To use vinegar, mix one part white vinegar with two parts water. Apply the solution to the affected areas with a brush or sponge and scrub away the mold. Be sure to rinse the area well when you’re finished so that all of the vinegar is removed.

Alternatively, you can also add some baking soda to the mixture. Baking soda is a mild abrasive that can help to scrub away mold spores.

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Oxygen Bleach

Oxygen bleach is a type of bleach that doesn’t contain harmful chemicals. It’s safe to use around plants and animals and won’t damage your deck.

To use oxygen bleach, mix one oxygen bleach and water. Apply the solution to the affected areas with a brush to scrub away the mold. Rinse the deck well when you’re done.

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Natural Deck Cleaners

While many available deck cleaning products use harsh chemicals, some natural options include Natural Choices Deck and Patio Cleaner. This product uses oxygen bleach as the active ingredient and is eco-friendly and non-toxic.

DIY methods like vinegar and laundry detergent will generally be cheaper than purchasing a specific deck cleaning product, but both options work.

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What We Don’t Recommend

There are some methods of removing black mold that we don’t recommend. One is using a wire brush. Wire brushes can damage the wood and leave behind scratches that provide a perfect place for mold to grow back.

We also don’t recommend using chlorine bleach. Bleach can kill mold, but it will also damage your deck by discoloring the wood and making it more susceptible to future mold growth. It’s also potentially hazardous to people and the environment.

Borax is sometimes considered a natural cleaning product, but there are some significant reasons for avoiding borax.

Finally, we don’t recommend using any type of chemical-based cleaner. These products may be effective at killing mold, but they can also be harmful to your health. If you must use a chemical cleaner, be sure to wear gloves and a mask, and ventilate the area well.

A Word of Caution for Painted Decks

If your deck is painted, you’ll need to be careful when removing the mold. Wire brushing or power washing can damage the paint and open up the wood fibers, making it even more susceptible to mold growth in the future.

If you have a painted deck, it’s best to remove the mold by scrubbing it with a hard brush and soapy water. You may also want to use a natural mold-killing solution like vinegar or tea tree oil.

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How to Kill Mold Under the Deck

Black mold can also be a problem on the underside of your deck board. Unfortunately, removing mold from under the deck can be more challenging. You can use the same methods, but you may need to take additional steps to protect yourself and whatever is below your deck.

Pressure washing is effective but potentially challenging depending on the height of your deck and the landscape below it. Another option is to spray a vinegar and water solution and then use a brush to scrub the mold away.

How to Prevent Black Mold On a Wood Deck

Once you’ve removed the black mold from your deck, you’ll want to take steps to prevent it from returning.

1. Apply a Mold and Mildew Resistant Sealer

One of the best ways to prevent black mold is to apply a mold and mildew-resistant sealer to your deck. This will create a barrier that mold spores won’t be able to penetrate.

Be sure to choose a product that is designed for use on decks. Some products are only meant for concrete or brick and can damage the wood.

You’ll need to re-seal your deck every one to two years, depending on the weather conditions in your area.

2. Keep the Deck Dry

Mold needs moisture to grow, so keeping your deck dry is an effective way to prevent it. If you have a pullout awning or any type of removable cover, remove it whenever it’s not in use. This will expose the deck to more sunlight and allow it to dry faster. You may also want to consider cutting back trees that prevent the deck from getting sunlight.

3. Remove Snow from the Deck

In the winter, be sure to remove any snow or ice that has accumulated on your deck. The wet snow will soak and penetrate the boards, leading to mold growth. An excellent way to do this is to use a plastic shovel. Metal shovels can damage the wood.

4. Check the Drainage

Make sure that the deck is drained correctly. If water is pooling on the deck’s surface, it could lead to mold growth. You may need to add additional drains or extend existing ones.

5. Clean the Deck Boards Regularly

One of the most important things you can do to prevent black mold is to clean your deck regularly. Even if you don’t see any dirt or debris, it’s important to regularly sweep and clean the boards.

If you live in an area with many trees, you may need to clean your deck more often. Leaves and other organic matter can fall on the deck and provide food for mold spores.

You should also hose down your deck periodically. This will remove any accumulated dirt or debris and lower the humidity level, making it less hospitable for mold growth.

6. Repair Cracks and Splits

Over time, your deck will start to show signs of wear and tear. It’s important to repair any cracks or splits as soon as you see them. These provide an entry point for moisture and can lead to mold growth.

You can use a putty knife and wood filler to repair tiny cracks and splits. For larger ones, you may need to replace the boards.

7. Remove Debris from Between the Deck Boards

Another way to prevent black mold is to remove any debris that has accumulated between the deck boards. This includes leaves, dirt, and twigs. You can use a putty knife or a small brush to clean the area between the boards.

Can Black Mold Grow on Composite Decks?

If you’re dealing with black mold on a wood deck, you might wonder if you could eliminate the problem by replacing the deck boards with composite deck materials.

While black mold can grow on composite decks, it’s not as likely as it is with wood. This is because composite materials are made from a combination of plastic and wood fibers. The plastic helps to resist mold growth, but it can still occur if the composite material isn’t cleaned regularly or if there’s excessive moisture.

However, not all composite deck boards are the same. Some are capped only on the top and sides, and others are completely capped on all four sides. Those capped on all four sides will be the most mold and mildew-resistant type of decking.

Related: How to Remove Mold from Clothes Using Baking Soda (and Other Methods)

Frequently Asked Questions

Why is my deck turning black?

The most common reason is the growth of black mold or mildew. This can happen if the deck doesn’t get enough sunlight or if it’s not properly cleaned and sealed.

How do I know if my deck has black mold?

One of the easiest ways to tell if your deck has black mold is by its color. Black mold will often appear as dark stains on the surface of the wood. Another way to tell is by its musty smell. If your deck has a strong musty smell, black mold is likely present.

Why does my deck have mold?

Mold can grow on a deck for a variety of reasons. The most common is excessive moisture. This can be due to poor drainage, improper sealing, or a lack of sunlight.

How do you remove mold from a wood deck?

There are several different ways to remove the mold, including pressure washing, using oxygen bleach, using a natural laundry detergent, using vinegar, or using a commercially-made deck cleaning product.

How do I prevent black mold on my deck?

The best way to prevent black mold is to keep the deck clean and dry. This includes sweeping it regularly, cleaning it with a hose, and repairing any cracks or splits. You should also seal the deck to help protect it from moisture.

Is it ok to power wash a wood deck?

Yes, you can power wash a wood deck. However, you need to be careful not to damage the wood. Use a wide nozzle and hold it about two feet away from the surface of the wood. Start at one end of the deck and work your way to the other. We recommend testing in an inconspicuous area first to make sure that it does not damage the wood.

Can you power wash mold off wood?

Yes, you can power wash mold off of wood. However, this will only remove surface mold. Other methods like oxygen bleach or vinegar may completely kill the mold.

Can I use bleach to clean my deck?

Yes, you can use bleach to clean your deck. However, you should only use oxygen bleach and not chlorine bleach. Chlorine bleach will damage the wood.

Black Mold On a Wood Deck: Final Thoughts

Black mold can be a nuisance on a wood deck. However, there are several ways to remove and prevent it from returning. Be sure to sweep the deck regularly, clean it with a hose, and repair any cracks or splits. You should also seal the deck to help protect it from moisture.

With these options available, black mold on a wood deck shouldn’t be a significant problem as long as it is addressed.

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