top of page

Black Spots on Cedar Deck: Causes, Treatment, and Prevention for Cedar Decking

black spots on cedar deck

A stunning red cedar deck is a great addition to your home - it adds a lot aesthetically and it’s the perfect spot for outdoor entertaining. As homeowners, we put a lot of time and effort into keeping our decks pristine, which is why black spots on cedar decking are such a nuisance. 

I have black spots on my new cedar deck - what should I do? You’re not alone. In this guide, we’ll explain everything you need to know about black spots on cedar decks. We’ll explain what can cause these dots, how to remove them, and how to prevent black dots in the first place. 

So, how can you make sure your beautiful cedar deck isn’t tarnished with black spots? Read on to learn how to keep your pride and joy in pristine, perfect condition, and save on potentially costly repairs and maintenance along the way! 

Quality Cedar Products can meet all your cedar board needs. This blog is informational only and not a replacement for expert advice. Please consult a professional before starting any building project as your needs and specifications may vary and it may not reflect the most current building codes, regulations, or industry standards.

Why Do I Have Black Spots on My New Cedar Deck?

First of all, why do I have black spots on my new cedar deck, and where did they come from? Once you understand what these spots actually are, we can talk about how to remove the black spots on cedar wood. 

What Are They?

Black spots on cedar decks are typically a form of discoloration that can vary in size and intensity. They may appear as small specks or larger blotches, often giving the wood a dirty or moldy appearance - they’re not nice to look at. 

While these spots are usually superficial, they can sometimes penetrate deeper into the wood, making them harder to remove. But what causes these black spots on deck wood? Let’s take a look at some common culprits. 

Common Causes

Mildew and mold thrive in moist, shaded environments, making cedar decks particularly susceptible if they do not receive adequate sunlight and ventilation. These fungi can quickly spread, creating unsightly black spots that mar the wood's natural beauty. 

Another cause of black spots on deck wood is tannins. Cedar wood contains natural oils and tannins that can sometimes rise to the surface, especially when the wood is exposed to moisture. These tannins can react with metals and other contaminants, resulting in dark discoloration or staining.

Metal contamination is another cause. Metal objects such as nails, screws, and patio furniture can rust and leach iron into the wood. When iron comes into contact with the tannins in cedar, it can cause dark, black stains to form on the deck surface.

Another cause is airborne pollutants like dirt, dust, and organic debris. These can accumulate on the surface of a cedar deck, and when mixed with moisture, they can form black spots that are difficult to clean.

Neglecting your deck can also be a problem - inadequate sealing, staining, or maintenance of a cedar deck can leave the wood vulnerable to the elements. Without proper protection, moisture can seep into the wood, promoting the growth of mold and mildew and tannin staining.

How to Remove Black Spots on Cedar Wood Deck Safely

So, what can you do about black spots on deck wood? With the right cleaning agents and techniques, you can usually restore your cedar deck to its original glory. Here’s a step-by-step guide to help you remove those ugly black spots from your deck. 

Choosing the Right Cleaning Agents

Selecting the correct cleaning agents is crucial for effectively removing black spots without damaging the cedar wood. Here are some good options:

  • Oxygen bleach: A safer alternative to chlorine bleach, oxygen bleach is effective in removing mold and mildew without harming the wood or surrounding vegetation.

  • Mild detergents: Non-abrasive, mild detergents can help remove surface dirt and stains.

  • Commercial wood cleaners: Specifically formulated for wood, these cleaners can target and eliminate black spots while preserving the wood’s integrity.

Avoid harsh chemicals like chlorine bleach, which can damage the wood fibers and affect the deck’s color.

Preparing the Deck for Cleaning

Before applying any cleaning solution, it’s important to prepare your deck. Remove all furniture, plants, and other items from the deck surface, then use a broom to sweep away loose dirt, leaves, and debris.

While your deck is clear, it’s a good chance to check for any damaged or loose boards and make any necessary repairs, like replacing any boards that aren’t in good shape. Check out our guides on how to sand a cedar deck, how to refinish a cedar deck, and how to install cedar deck boards

Applying the Cleaning Solution

Once the deck is prepared, it’s time to apply the cleaning solution. Follow the manufacturer’s instructions to mix the cleaning agent. For oxygen bleach, dissolve the powder in warm water as directed. 

Use a garden sprayer or a brush to evenly apply the cleaning solution to the black spots on wood deck boards. Ensure the solution covers the black spots thoroughly. Let the solution sit on the surface for the recommended duration, usually 10-15 minutes, to penetrate and loosen the stains.

Make sure you understand the type of wood your deck is made of, as the manufacturer’s cleaning instructions may vary for redwood vs cedar decks, pine vs cedar decks, or douglas fir vs cedar decks

Scrubbing the Deck

After the cleaning solution has had time to work, it’s time to scrub the deck. Use a soft-bristle brush to avoid scratching or damaging the cedar wood. Work in small sections, gently scrubbing the black spots on wood deck boards in a circular motion. 

Apply moderate pressure to lift the stains without harming the wood fibers of your deck boards. If you have really stubborn black spots on cedar wood, you may need to repeat the cleaning and scrubbing steps again to lift them.

Rinsing and Drying

The final step is to thoroughly rinse and dry your deck. Use a garden hose with a spray nozzle to rinse off the cleaning solution and lifted stains. Don’t use a pressure washer, as the high pressure can damage the wood.

Make sure all traces of the cleaning agent are removed to prevent any residue from affecting the wood, and let your deck air dry completely before replacing furniture or applying any sealant. This may take a few hours to a day, depending on the weather conditions and how much sun your deck gets. 

Tips on Preventing Black Spots on Cedar Deck Going Forward

We’ve explained how to deal with black spots on wood decks, but wouldn’t it be easier if you didn’t have to scrub away at your deck to remove the spots? The good news is that black spots on cedar wood are often avoidable - here’s how to prevent them. 

Regular Maintenance

People always ask us how long does cedar decking last. The truth is, it last much, much longer if you learn how to protect a cedar deck, how to care for a cedar deck, and how to clean cedar decking

Regular maintenance is key to preventing the buildup of dirt, mold, and mildew, which can lead to black spots on cedar deck wood. Make sure you’re sweeping your deck regularly, washing it every few weeks, and doing a seasonal deep clean to keep your deck pristine. 

Staining a cedar deck is also a great way to protect your cedar wood, and painting cedar decking is another option to extend the lifespan of your deck and reduce the chances of black spots on cedar deck boards. 

Using a Sealant

Learning how to seal a cedar deck is another way to prevent black spots on deck wood. A quality sealant provides a protective barrier against moisture and other elements that contribute to black spot formation. 

Select a sealant specifically designed for cedar wood that offers protection against UV rays, moisture, and mildew. Transparent or semi-transparent sealants are often preferred for preserving the natural look of cedar.

Reapply the sealant as recommended by the manufacturer, usually every 1-3 years. This ensures the protective layer remains intact and effective. Use a brush or roller for even coverage, and pay special attention to end grains and joints where water can penetrate.

Ensuring Sun Exposure and Ventilation

Sunshine and good ventilation help keep your deck dry, reducing the likelihood of mold and mildew growth and the black spots that can come with them. Trim back any overhanging branches or nearby plants that can cast shade and trap moisture on the deck surface. 

Keep the deck surface as uncluttered as possible to ensure good air circulation. Avoid placing large, solid objects directly on the deck for extended periods, as they can create damp spots which can later lead to black spots.

If you’re planning to build a new deck or renovate an existing one, add design features that enhance ventilation. Make sure you understand cedar deck board spacing for airflow, and make sure there is adequate clearance between the deck and the ground.

Wrapping Up Our Guide to Black Spots on Cedar Deck Boards

Let’s face it, with all the time, effort, and money you’ve put into your deck, you don’t want it to get covered in unsightly black spots. Learning how to prevent these spots, and how to treat any that do show up, is key to keeping your beautiful cedar deck in prime condition. 

One of the best ways to prevent black spots on cedar deck boards is to start with the best quality cedar deck boards and cedar timbers available. Here at Quality Cedar Products, we only offer the best in premium cedar boards for sale

From clear cedar to tongue and groove cedar, we have a wide range of quality products for your next project. We manually sort and grade all our cedar lumber, ensuring we sell you nothing but the absolute best - we want your deck to look stunning and last forever too! 

Enjoy a stress-free process when you order cedar lumber online from us - our money-back guarantee means you can simply turn our truck around if you aren’t 100% satisfied with your order. We’re builders ourselves, so we know that every project needs to start with the best possible materials. 

Don’t settle for second-grade cedar that causes black spots on your deck - invest in hand-sorted, premium cedar wood backed by our team at Quality Cedar Products. 

G&B Wholesale Lumber Incorporated does not assume any liability for the accuracy, completeness, or usefulness of the information provided in this blog post. The reader is solely responsible for any actions taken based on the information presented. Any reliance on the information is at the reader's own risk.


G&B Wholesale Lumber Incorporated is not responsible for any loss, injury, or damage that may occur as a result of following the suggestions, tips, or recommendations provided in this blog post. Building projects involve inherent risks, and it is essential to exercise caution, obtain proper permits, and engage qualified professionals to ensure safety and compliance with all applicable laws and regulations. The inclusion of external links, references, or recommendations in this blog post does not constitute endorsement or guarantee the quality, reliability, or suitability of the linked sources. The reader should independently verify the information and assess its relevance to their specific circumstances. The author reserves the right to modify, update, or remove the content of this blog post at any time without prior notice. It is recommended to check for the most recent updates or consult with professionals to ensure the information is current and applicable. By reading this blog post, the reader acknowledges and accepts the above disclaimer and agrees to use the information provided responsibly and at their own discretion.

141 views0 comments


bottom of page