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How to Prevent Mold in Your Shed

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Mold and mildew are things that nobody wants to find in his shed. They indicate not only a moisture problem, such as a leak, but indicate that the problem has gone on long enough to allow fungi to enter and grow, perhaps even long enough to cause rot.

The 3 steps for preventing mold in your shed is controlling the humidly, not allowing any moisture to remain and to use a dehumidifier or have a good source of ventilation.

If you’re wondering how mold could get into your shed, the answer is that fungi propagates by shedding spores. These spores are so small most can fairly float in the air, and most can’t be seen with the naked eye unless you step on a ripe puffball mushroom, in which case you’ll cause a cloud of them to poof upward.

The mold spores can float on a breeze into your shed or can be carried in clinging to your yard tools. All they have to do is brush against a damp cardboard box or plywood siding and they settle in and propagate. While fungi don’t grow on metal, their spores can certainly be carried into your shed on metal tools. This is one reason that you shouldn’t put any tools away unless they are dry. Rust isn’t the only potential problem with that.

How Do I Get Rid of Mold in My Shed?

If you notice sooty or slimy black spots on things in your shed, on the walls or studs, or the flooring, you probably have mold. A strong musty odor is another indication. Even if you don’t have mold per se, the musty smell indicates some kind of fungus.

Any kind of fungus in your shed is not good. This calls for seeking out the mold or mildew and cleaning it up. Then comes the most important part, which is figuring out what allowed its development in the first place and taking steps to change the relevant conditions.

Fungus forms in moisture, but some can live in drier places afterward. Mold needs three things to grow, thrive and multiply: moisture, oxygen and warmth. Your shed may not seem warm to you, but it could get warm enough at times to encourage mold growth. Existing mold can’t multiply under dry conditions, but that doesn’t mean it dies when the weather dries out. It just exists until it gets more moisture and can begin producing spores again. If your dealing with a musty stench check out my article How to Get Rid of Musty Odor in Shed? for more information and how to remove it.

Is Vinegar or Bleach Better for Killing Mold?

Many people believe bleach is a real mold killer, but actually, vinegar does a more thorough job of killing fungi. Even the EPA does not recommend using bleach on mold. The agency states that some mold spores still remain after bleach application.

Bleach will kill the surface mold, but not the membrane of filaments underneath, meaning that the mold will grow back. The mold may even recognize the bleach as a threat and later grow back stronger. When bleach is applied to porous materials such as wood or drywall, mold membranes actually move deeper down to avoid the bleach.

White vinegar is the best kind to use for mold cleaning. While regular vinegar usually has five percent acidity, you may be able to get cleaning vinegar, which has six percent. One brand isn’t any better than any other, so go ahead and get the generic while vinegar. Be aware that there are a few surfaces that can be damaged by vinegar, such as natural stone, waxed wood, aluminum and cast iron.

How to Kill Mold on Walls?

Plain, white vinegar is best for not only cleaning mold off your walls but also preventing it from growing back. It gets to even the parts of the mold that aren’t readily visible. It’s actually a worse threat to the mold than bleach.

Pour vinegar into a spray bottle and spray it onto the mold spots and surrounding area. Wait an hour at least, then wipe it off. It’s great on drywall and wood products such as plywood or Oriented Strand Board as long as the wood hasn’t been waxed.

This procedure can be used almost anywhere, not just on walls. Put on protective clothing and gear as described below before cleaning away mold spots. Use a spray bottle with straight vinegar and spray it on the mold and the area around it to get any invisible spread. Let it stay for at least an hour, then wipe away.

If you need more help to get out the stain, use a stiff brush, dip it into a container of hot water, and then a dish of baking soda and scrub. Be prepared to put some elbow grease into this, as you want to ensure you get all the filaments that may be hiding. Blot up the excess moisture, then let it dry.

Do I Need to Do a Mold Test?

If you should see some blackened spots on your shed wall but don’t know if it’s mold or dirt, there’s an easy way to check. Dab a little bleach on the area and wait a few minutes. If the area turns a lighter color, you have mildew. If it doesn’t change color, it’s just plain dirt.

If you see mold, you don’t need to do a test. However, if you find a place or two inside your shed that is damp or looks like an entry point for moisture but can’t see any visible mold, you don’t have to call for a professional mold inspection. There are home test kits on the market that will do the job just fine.

The best way to find mold is to find the moisture source. You’ll need to find that source anyway to rectify the situation. One of the easiest ways is to really go over your shed carefully after a good rain and check for damp spots. Small leaks can cause the biggest problems, as they aren’t as obvious as a leak causing a steady drip on things or on your head.

A small leak can go undetected for a long time, allowing moisture to seep into the walls or framing and giving mold and mildew a good start and place to grow. This means that you’ll have to clear out the shed to check everything, but you’ll need to go through everything anyway if you have mold problems to either clean or discard affected items.

Check all around any openings such as window frames, vents, the base sill plate, and the top sill. Check over the underside of the roof, especially in places where flashing was installed above. Don’t rush this check; you want to look into all the nooks and crannies. If you find damp or suspect wood places, probe them with a screwdriver or other sharp object.

If the wood feels soft or it crumbles, mold has already started to rot the wood. If you find a musty smell in a place but don’t see any sign of moisture, you may have to dig deeper, such as peeling back the insulation to check underneath.

Do I Need to Wash Down Everything?

If you discover mold or mildew in your shed, that doesn’t mean that you have to wash down all the walls or the underside of the roof. You can wash just the affected areas with vinegar as outlined above. You probably should clear out the shed to check for items affected by mold.

You’ll need to do this anyway to make a thorough check for moldy or damp spots in the shed to begin with. Check over all items thoroughly. If they smell, even if they don’t seem affected, assume they have spores and need to be cleaned or discarded. Mold can come in other colors than black, such as brown, green, yellow or even white, so don’t just look for black spots.

If you find items with mold, your best bet is to discard them if you can live without them. Other things can be cleaned depending on the material. Porous things such as cardboard and paper products should be discarded. If a cardboard box used for storage has been affected, check all the items inside for mold, then repack them in a different box.

Trying to clean the box itself isn’t worth the effort. Besides, the fact that it had mold means that it has gotten damp at some point even if it isn’t at the moment, and the structure itself has been weakened.

Clothing or other cloth items can be salvaged with thorough washing and disinfecting. However, cloth items really are not suitable for storage in a shed in the first place, so another place in the house should be considered.

Electronics shouldn’t be stored in a shed, but if you have some, it’s hard to tell how they may have been affected. Spores could have drifted inside and been hard to spot, not to mention the fact that you’d have to take the item apart to find them. If your item has been stored near a known mold spot, it probably should be discarded.

What Safety Precautions Should I Use When Cleaning Mold?

Once you start working on cleaning mold, the spores will start to disperse into the air. You won’t even see them, but they will find their way into your sinuses, causing at the very least some irritation.

While you probably won’t be dealing with the much-publicized toxic mold, any kind of mold can cause or worsen existing health problems such as COPD or asthma. Many people are naturally allergic to mold and may not be aware of it until they come into contact.

When working with mold, wear long sleeves and long pants, along with eye protection, a respirator rated for mold and rubber gloves. Since the spores will cling to your clothes, it’s best to make a plan for removing the clothing right after you get into the house and get it into the washing machine with the least disturbance possible.

You could also choose some coveralls over your regular clothing that you can remove outside, then put into a bag. Carefully spraying water over the clothing inside the bag before removing it and putting it in the washer should help keep the spores from flying around.

How to Prevent Mold from Coming Back in Your Shed

There are two good ways to keep mold from coming back into your shed. One is to go over all seams around the outside, including all window, door and vent frames with caulk. Also, seal siding seams if possible, and the top plate where the walls meet the roof.

Check the roof thoroughly for broken or missing shingles and replace them. Check around any flashing and caulk that also. You’ll need to check periodically, as caulk does eventually dry and crack with the weather and needs to be replaced when it does.

The other good way is with proper ventilation. If you have moisture coming in that’s not from a leak, you need ventilation or more of it. Moisture seeps up from the ground and can seep up from a concrete slab even with a vapor barrier from rainwater contacting the sides of the slab.

Moisture can also collect on a hot, humid day when it comes into contact with the cooler slab. It eventually creeps up into your shed. If your shed is raised, the airflow underneath will help prevent moisture from collecting on the underside of your shed base, but not stop it entirely. If you live in an area with a lot of rain or long periods of high humidity, the moisture can’t readily evaporate into the atmosphere and can collect underneath the shed.

Ventilation inside helps by keeping air moving, which makes it hard for moisture to condense. In addition, the proper airflow will allow moisture-laden warm air to rise up and out, carrying its moisture with it. A vent on each gable set into the wall with a turbine or box vent on the roof is a simple scenario that will allow air to come in and go upward and out the top and will also draw the inside air up with it. For more information check out my article Should I Install a Roof Vent for Shed Ventilation?

Will a Dehumidifier Help with Controlling Mold?

A dehumidifier will help keep down moisture, which prevents mold growth and spread. Many people, however, don’t have electricity run to their shed, and these machines need to be plugged in. There are battery-operated models available, but they won’t handle the square footage of larger sheds.

If you do have electricity in your shed, it’s probably best to work on other ways to cut down on moisture, such as adequate ventilation rather than depending on a dehumidifier. You can still run the dehumidifier occasionally on extra humid days or days when the weather prevents you from opening and airing out the shed for several days.

Should I Treat the Inside of My Shed with an Anti-Mold Solution?

There are several products that kill mold and prevent it from coming back. Some require rinsing off after a time while others just need to be sprayed on. None of them is a permanent solution.

You’ll still need to find the underlying moisture problem and deal with it or the mold eventually comes back. Usually, cleaning wood and other materials with vinegar is sufficient to not only kill the mold but discourage it from returning, at least for a time. If you live in a humid or rainy area, you may want to try something else.

What Natural Non-Toxin Ways Can I Use to Remove Mold?

  • Vinegar is the number one choice to remove mold, especially since it discourages the mold’s return.
  • Baking soda comes in next, but sources are divided as to whether you can leave it on the affected area or need to rinse it off after scrubbing.
  • Tea tree oil is touted as a natural fungicide that can be used to clean off mold as well as discourage spore growth. Use one teaspoon of the oil per cup of water in a spray bottle. Allow it to dry, then wipe off the excess. Gloves should be used, as the oil can irritate the skin. The scent should go away in a few days.
  • Grapefruit seed extract and other citrus seed extracts contain natural acids that act on mold. Mix in a spray bottle at about ten to twenty drops to a cup of water, spray on, then let it set from ten minutes to an hour before wiping off the residue.
  • Orange peel oil can also be effective, especially if the peel is soaked in vinegar. Some prefer to use half an orange applied directly to the mold.
  • Hydrogen peroxide can clean mold and prevent regrowth, but it’s not suited to apply to every surface. If in doubt, try it out on a small place to see the effects.

A combination of baking soda, vinegar and lemon juice can work together to combat mold. Mix equal parts vinegar and lemon juice with a lesser amount of baking soda to form a thick paste. Spread it onto the moldy areas and scrub. Leave it on for ten minutes or so before washing with plain water.


If you discover mold in your shed, you’ve got some work ahead of you. Discovering the source of the mold, cleaning it, and fixing the problem that let in the moisture to begin with are not easy. Neither is going through the contents of your shed to see what might have been affected.

However, once you have cleaned up the mold, taken care of the cause of the moisture, and perhaps increased the ventilation in your shed, you shouldn’t have to deal with this problem again.

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