April 25

Identifying Molds and Mildews on Your Deck

Springtime is here, and it is finally deck season again. You’ve got your grill set up and your outdoor furniture arranged perfectly for entertaining friends and family. Then you see it. An unsightly, discolored patch of wood, sticking out like a sore thumb.

When in their earlier stages, molds and mildews just look bad on your deck, but they can cause serious damage if ignored.

Diagnosing a Growth on Your Deck: Mold, Mildew, or Algae?

Any living thing that takes up residence on the surface of your deck is going to impact its appearance. If left unchecked,  the structural integrity could be at risk. Mold, mildew, and algae are particularly troublesome, but if you catch them early they are completely manageable.

Before we can figure out which treatment is best, we need to learn how to identify the difference between these problems. Mold is a fungal organism that grows in the outer layers of your decking boards, starting on the surface and spreading into the wood grain. It spreads naturally via spores that land on your deck, before sending down tiny filaments to break down the organic matter as a food source. You can identify mold by its furry and slippery growth which protrudes out in clumps. Mold will most often show as black or dark grey and green patches that might become lumpy as they get larger.

Mildew is biologically very similar to mold and is the name commonly given to the early stages of different species of fungi. These fungi progress from a mildew stage into a mold, so the name is also used for early mold infestations.  Mildew spreads through spores and establishes itself on the outer layer of wood. Unlike mold, mildew won't or hasn't yet penetrated the surface. Luckily for you, this means that mildew can be wiped off much more easily.

Mildew looks more like a white or gray powder that someone has dropped on your deck and is most often just flat spots of discoloration.

Algae is completely different from both mold and mildew. While mold and mildew are fungi, algae is a basic species of plant. It will present a slimy green film across your deck, and will most often grow in the wettest area of your deck.

Because algae is a plant, it doesn’t ‘feed’ on your deck as much as mold does, but it will absorb some nutrients from the organic matter in timber. It also retains a lot more moisture as it grows. This moisture will eventually get into the wood grain and cause issues by providing ideal conditions for other infestations.

Dry Rot

Dry rot is a different issue altogether. Like mold and mildew, it is caused by a fungus that colonizes and takes root in moist wood. The fungal organism then grows and covers the boards as it consumes the wood and the moisture within it. As this progresses, the dry rot fungi cause the wood to decay while it extracts all the moisture from your deck, leaving behind warped and brittle remains.

The fungus needs a moist environment to survive, so it only occurs on timber that regularly gets or remains wet. You may experience dry rot due to a shaded deck that never dries after rain, or because of leaking pipes, roofs, or gutters. You can see the fungi covering the wood with a woolly mycelium, its root-like network for future expansion. You can also identify it by warping, brittle, or cracking wood, and by a damp, moldy smell.

Dry rot is an issue for decks, and it should be dealt with immediately. It can compromise the structural integrity of your supports and joists, as well as the boards on top.

How to Remove Molds and Mildews

If your deck has mold, mildew, or algae on it, you’re going to want to get in and remove it as quickly as possible. Not only will you stop them before they cause any severe damage, but you’ll also keep the natural wood of your deck looking its best.

The most important thing to consider before starting removal is to identify possible causes of the issue. Both algae and fungal invasions need moisture to survive, so it’s sensible to address any leaks that might be causing your deck to trap standing water or have poor drainage.

Fixing broken or leaky downpipes or roof gutters is always a smart idea, and addressing poor drainage in your yard can help prevent issues from coming back. It can also pay to let a little more sunlight onto your deck, which will help stop a lot of molds and mildews from growing. You may need to do a bit of tree trimming or start retracting any awnings over the deck more regularly.

Manual Removal Techniques for Fungi on Your Deck

The cheapest way to remove molds and mildews is by applying some good old-fashioned elbow grease and removing it manually. Keep in mind that this won’t work for advanced cases, or most infections of dry rot.

Before you start scrubbing, it’s important to ensure you have the appropriate protective equipment to keep yourself safe. Inhaling mold spores can cause severe health issues, so a respirator or mask rated for biological particles is a must. It’s also prudent to wear eye protection and gloves, and you should cover any exposed skin. Even a thin layer can help prevent any spores from getting into places they shouldn't.

Sweeping, blowing with a leaf blower, or vacuuming your deck to remove any mold spores is a good first step in manual removal. Doing this will mean that you’re less likely to have new areas of infestation pop up after you've finished.

You can now either continue to sweep or scrub your deck with a soapy water blend or with white vinegar diluted with water. Both of these liquid blends combined with a stiff-bristled brush or broom will remove most cases of mold, mildew, and algae from a deck. Give it all a solid scrub, then wash it down with a hose or bucket of clean water. Ensure that you test any brushes on a discreet part of the deck first – some brush materials can scour the surface of softer woods, leaving you with a fresh problem after cleaning up.

If you want an easier option, then getting your hands on a pressure washer is another option. Most pressure cleaners will have enough power to get the mold out of the timber grain, but be careful with the nozzle you choose. You don’t want to overdo it and damage your wood. Check out our full guide on pressure-washing your deck, for more information.

If you have a particularly bad case of mold, you may have removed all the vegetative mass, but the wood is still stained. In this case, you might need to lightly sand the area, either by hand or with a belt sander. Be sure that you are using the right grit of sandpaper for your deck’s wood type, and be prepared to touch up the stain once you’ve sanded a layer off.

Choosing the Right Chemical Treatments for Your Deck

If you’ve tried manual removal and can’t remove all the mold from your deck, there is always a more advanced option available. Maybe you're not in the position to spend the time and energy needed for an afternoon of hard scrubbing. Maybe you’re having a cookout this weekend and didn’t notice mold until it was too late. For any homeowner looking to quickly defeat their local fungi, there are always chemical treatment options available.

There are a lot of different chemical treatment types available. These range from specific fungicides and herbicides that will kill the organism itself, to cleaning agents which will seep into the wood to bleach stains and kill any spores.

Be aware that some chemical wood cleaners and fungicides are hazardous to any humans, animals, and other landscaping they come in contact with – so choose your solution with that in mind. Woodrich Brand is proud to offer the Environmentally Friendly Cleaner (EFC-38) wood cleaner and mild stripper. The unique formula of EFC-38 tackles mold, mildew, and algae, in a simple, effective, and safer system than other wood cleaners.

Protect Your Deck with a High-Quality Wood Stain

After you have identified the growth on your deck and removed it with muscles or premium treatments, it is time to think about the future.

EFC-38 Wood Cleaner & Mild Stripper will also remove a wide range of stains and sealers, so this may be the perfect time for a deck restoration project. Re-staining your deck with a high-quality oil-based stain will defend your wood from future fungi and algae attacks. Not only will your deck look new and impress your friends and family, but you won’t have to deal with frustrating mold next spring.

Our project support team is ready to help you start this year off right, by improving your deck’s appearance, lifespan, and protection for the future. For personalized recommendations and guidance, contact us at (636)-288-8512 or send an email to support@woodrichbrand.com with a picture of your mold, mildew, or algae. You will know what to do in no time – we’ve seen it all before.


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