Remove Black Mold on Deck Wood In 3 Ways [Reasons & Prevention]

You must be introduced to black mold long ago if your property includes a deck. Mold and mildew growth is very common outdoors, especially on deck wood. Decks are generally placed in wet or bowery areas. Hence, black mold growth is obvious in there. Even though black mold takes place following the rules of the ecosystem, it can offer negative consequences.

Black mold and mildew are not safe for your property and health. It is a kind of fungus that causes the decaying of your deck. Deck wood becomes rotten if you do not clean off the black stain frequently. Having said that, black mold and mildew on deck wood need to be removed the moment you notice it.

However, getting rid of black mold on your deck wood doesn’t require professional help always. You can clean it by yourself as well if you know the proper way. Luck on you, today, we are going to cover you with the ways and everything about removing black mold and mildew from wood.

Black Mold on Deck Wood

Reasons Why My Deck is Turning Black:

If your deck is turning black, it is obviously growing black mold. There are many reasons why black mold is taking place all over the deck wood. Let’s get to the reasons.

a) Wet Deck:

wet deck wood

This unsightly fungus manages to grow on a material when it is wet always. It also grows on materials that are highly filled with cellulose. Materials including lumber, gypsum board, fiberboard, and all, are suitable for black mold growth.

However, in the case of deck wood, most of the time it remains moist. Due to the humid climate and hot weather, moisture in the deck wood takes place. In this situation, if you do not clean your deck on a regular basis, the micro fungus takes advantage.

b) Unsealed Deck:

Unsealed Deck wood

Again, deck wood not sealed with adequate and proper sealant can also be a reason why your deck is turning black. Since, after rain, deck wood takes a long time to dry, the area becomes more suitable for black mold.

c) Thickly Stained Deck:

A thickly stained deck is also one of the reasons. If you overly apply deck stain on your deck wood it creates a thick layer. Again, the thick layer takes a drying time of several days. Within this time the stained deck gets contaminated by the dirt and pollen of trees.

These contaminants get stuck with the stain and provoke black mold to breed.

d) Oil and Water-based Stains on Deck:

There are mainly two types of stains available for the deck. One is an oil-based stain and the other is a water-based stain. Water-based stain doesn’t include any chemicals in it. Hence, it offers less chance of mold growth.

On the contrary, oil-based stains are made with many additives. These additives can be a reason for promoting mold growth. However, the best oil-based stains come with algaecides in them. It helps in declining mold growth.

So, these are the probable reasons why black mold grows its kingdom on your deck. However, places, where the deck wood gets even a little sunlight, can also be affected by this fungus. Then again, as water-based stains are not durable and fail many times, it can also grow mold.

What Kills Black Mold & Mildew on Wood:

There are many cleaners and solutions available in the market to clean off black mold. Professionals out there most of the time use commercial cleaners. Again, there are DIYers who like to use natural and homemade cleaners to get rid of black mold from their deck. You can try on the following cleaners to kill the mold on wood.

1. Commercial Mold and Mildew Deck Cleaners:

There are many cleaning solutions for wood cleaning. These cleaners are used for normal dirt removing and brightening of the wood deck. Again, some of these commercial cleaners are also used to kill mold, mildew, moss, and other fungal elements.

moss mold mildew algae stain remover - wet&forget

Mixing a generous amount of cleaner with water, these cleaners are used. Moreover, the cleaners with concentrated formula contain mildewcide in them that helps in the faster removal of mold and mildew. Also, it provides a future protection barrier to the deck for mold regrowth.

2. Trisodium Phosphate (TSP):

Klean Strip TSP No Rinse Substitute Cleaner

Trisodium Phosphate is also an effective cleaner of black mold. It comes in a powdery texture. It is also considered an industrial cleaning material. Mixing 1.5 cups of TSP with two gallons of water, the solution is made.

However, using TSP has some side effects. If carefulness is not ensured, it can harm the landscaping and environment.

3. Oxygen-based Bleach:

Non Chlorine Oxygen Bleach

This material is also helpful in killing black mold. Solution of water and bleach works well on some materials. But in the case of the wood deck, it might leave a negative effect on it. The fibers of the wood can be damaged by using bleach.

Again, bleach cannot penetrate the wood properly. Hence, it cannot clean the mold through its roots. Thus, with bleach, the clean is undone sometimes and it provokes mold regrowth. Read Also: 6 Best Chemical Resistant Spray Bottles for Bleach Solution.

4. Distilled White Vinegar:

Natural Distilled White Vinegar

Vinegar is one of the most popular natural elements for cleaning off mold. White distilled vinegar is hugely used for indoor moss infestation. However, it can also be used for outdoor black mold attacks. Hence, to remove black mold from your deck wood, you can use white vinegar.

5. Detergent:

Detergent especially the laundry one is also a good cleaner of mold from the wood deck. Mixed with water, it can remove mold effectively. Unlike bleach, detergent can rich out the mold roots and offer deep cleaning.

6. Pressure Washer:

clean deck Electric High Pressure Washer

This is another way you can kill the black mold on wood. You won’t need any other chemicals or cleaners if you use a pressure washer. However, while using a pressure washer you need to be a bit careful. Only the proper use of the pressure washer can help you out with the removal of black mold.

The pressure washer not only removes black mold but also brings back the previous brightness of the wood. However, delivering excessive pressure can damage the wood. Especially while using the pressure washer on the softwood, be extra careful.

3 Ways to Get Rid of Black Mold on Deck Wood Fast:

Now that you know the materials that can be used to remove the growth, you have to know the process. Well, apart from the pressure washer, all the described materials are used in the same way to get rid of the mold. You will know better when you know in detail.

1. Removing Black Mold With Pressure Washer:

Removing Black Mold with Pressure Washer on Deck

Many choose to deal with a pressure washer for faster removal of mold and mildew. A pressure washer is a powerful tool that comes with a wider range of pressure. It can create a pressure of water of about 2,000psi or more. However, to deal with mold problems on deck wood pressure of about 1500psi would be enough.

Whereas for usual deck cleaning you need pressure around 800psi to 1000psi, for mold cleaning 2000 will create excess pressure. Again, a nozzle with a 40 to 60-degree wide angle will also be required. Make sure you do not choose a nozzle with a narrow tip.

Using the nozzle, spray the wood deck systematically. Make sure you are spraying from up to two feet away. Spraying too close to the deck can damage the wood. If the mold infestation is highly significant then first apply a cleaner with a soap dispensing pressure washer.

Starting from the deck inside the corner, wash the place systematically. When you are done pressure washing all over the deck wood rinse the deck using a garden hose. Clean off the soap from the deck so that it doesn’t become slippery.

For your information, using the pressure washer on softwood requires only pressure of about 500 to 600psi. More pressure will decay the softwoods including cedar, pine, and all. Likewise, you also need to be careful with the hardwood as well.

2. Cleaning Off Mold without Pressure Washer:

If you are not using a power tool then you have to go for the cleaning solutions to get rid of the black mold and mildew. For that, you will need the equipment or essentials written below.

Required Essentials:

  • Cleaners
  • Water
  • Spray bottle
  • Soap
  • Bucket
  • Sponge or bristled brush
  • Mask
  • Gloves
  • Eye protector

Get all these essentials together before you get started with cleaning off the black mold.

Now that you have got all the essentials, get to the cleaning process step by step.

Step-1: Ensure Protective Gear:

Ensure Protective Gear

Since, the black stain can affect your health as well, make sure you wear all the protective gear. The smell from the mold spores can invade your respiratory system if inhaled. So, wear a mask, gloves, eye protector, and wear other protection.

Step-2: Vacuum the Deck:

vacuuming the moldy area on deck

This is the next very important step. To loosen the spores of the black mold vacuuming the area is important. Using a HEPA filter vacuuming can be done. It helps to suck up the mold spores and lose them for easy cleaning.

After vacuuming, make sure the contents are disposed of well. Put the vacuumed contents in a plastic bag and seal it well so that the spores cannot escape and infest further.

Step-3: Make the Solutions:

Now, in this step, making a cleaning solution is important. Depending on the infested area, a cleaner should be chosen.

  • If the mold yet not has affected the deck wood deeply penetrating the material then a simple detergent or soap solution will work. Adding a teaspoon of detergent or soap to a spray bottle, fill it with water. Then shake the solution properly in the spray bottle.
  • However, there are chances only using soap solutions won’t always work. In this case, use white vinegar with tea tree oil. Distilled white vinegar is highly effective and it is capable of removing mold species of 80% and more. Mix vinegar and water at the same ratio rate in a spray bottle and add a spoon of tea tree oil. Then shake the bottle well.
  • Again, if all the mentioned solutions fail, then get a commercial or industrial mold and mildew cleaner. For severe black mold infestation, these cleaners can help you out. They come in liquid solutions. Mixing with water the solution needs to shake in a spray bottle.

Step-4: Spray Solutions on Black Mold:

After making the solutions in a spray bottle. Spray the solution all over the mold-infested place. While using soap solution, after spraying it use a brush with soft bristle to rub gently. The sponge can also be used to scrub the area.

Again, if you use a vinegar solution, leave the place to dry for an hour after spraying. Within one hour it will react with the black stain on the wood deck. When it is dried on the surface, using a moistened rag or cloth wipe the deck. After that, using a dry towel wipe it again. However, by using a dehumidifier the deck will dry faster.

Step-5: Sand the Deck Wood:

Sand the Deck Wood for off mold

This is an optional step. It only should be done when it is necessary. In many cases, small traces of stubborn molds get stuck with the wood even after cleaning. It creates a black spot or stain on the wood surface. In this situation, sanding is the last option.

Nonetheless, use only sandpaper of 100-grit. With the sandpaper rub the deck wood gently. Do not get overwhelmed while rubbing. Sanding too much will damage the deck wood. To remove the dust after sanding vacuum the place.

3. Cleaning Off Mold from Stained Deck Wood:

using vinegar to off mold

Mold and mildew growth is not that common with painted or stained deck wood. Nonetheless, black mold can start growing if the stain fails in the very beginning. However, to remove the mold and mildew growth from stained deck wood. You can simply use the dishwashing detergent mixing with warm water.

Take the regular usable 2 to 3 spoon of detergent per gallon of water works well on it. Spraying over the stained wood, scrub it gently. As a tip, do not use bleach on stained deck wood. It will discolor the surface.

Again, to deal with stained deck wood, a pressure washer is not supposed to be used. There are chances of stripping off the paint from the wood deck if the pressure washer is used. Also, using vinegar will help to prevent penetrative mold.

Prevention from Black Stains on Wood Deck:

To deal with many adverse situations including black mold, prevention is always the better option than cure. If you manage to stop the growth of black mold in the very first place, then there will be no chance of further growth. To prevent black mold, you can consider the following points.

a) Keep the Deck Dry:

Since, the wet deck is highly susceptible to grow black mold, keeping it dry is necessary. Make sure your deck wood gets enough sunlight every day. It will keep the deck dry and prevent black mold and mildew. Again, if you own a deck awning, make sure it is rolled allowing the deck to have some sunlight.

b) Use Mold and Mildew Resistant Sealant:

Sealing is also a good solution to prevent black mold on deck wood. However, sealing deck wood using a water-based mold and mildew-resistant wood sealant will be appropriate. Sealing the deck each year with this type of sealant will prevent the deck wood from swallowing the moisture.

The sealant also helps in the fast dry of the deck wood after rain. So, the chances of mold growth become lower.

c) Use Quality Stain:

Best quality stain helps in preventing mold growth on deck wood. A high-quality stain boasts quick-drying properties. Also, the best stain contains herbicide additives to prevent the deck from pollen and dirt. So, mold cannot breed as well.

d) Clean the Deck Frequently:

To not provide the mold with food, clean the deck wood on a regular basis. Pollen, leaf clumps, sticks, and many debris materials are food for mold. So, to stop promoting mold growth keep cleaning the deck surface properly.

e) Re-route Water Away from Your Home:

To save your deck from being wet, it is important to re-route the water away from home. Otherwise, the deck wood will remain wet and inspire mold growth.

f) Shovel Snow off Your Deck:

To prevent mold and mildew, ensuring a dry environment is important. However, it is not always possible especially when snowfall occurs. The best you can do is shovel the snow off your deck from time to time.

g) Use didecyl dimethyl ammonium chloride Chemicals:

Use Chemicals on deck wood

Lastly, if nothing works and you own a bare wood deck then you can try on some chemicals. The most used and recommended chemical you can use is didecyl dimethyl ammonium chloride. It is highly effective but it can be erosive to the skin. Again, you can also use chlorothalonil and Mildew-X, to prevent mold colonies.


Question: How to get rid of mold on pressure-treated wood?

Answer: Pressure-treated wood or lumber can also give birth to mold growth. However, using the same steps written above, the mold on pressure-treated wood can be removed. Again saying, do not use bleach. It causes damage to the pressure-treated wood as well.

Question: Does black mold destroy wood?

Answer: If you still stick to us, you must know now how dangerous is black mold on deck wood. If the mold and mildew get enough time to increase their realm, it will start eating up the wood. Gulping the surface nutrients of the wood, mold gradually weakens it. Hence, the wood becomes rotten eventually and destroys the wood.

Last Updated on October 17, 2021 by Rogers Weber

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