How to Find, Kill and then Prevent Garage Mold


Mold is a dangerous fungus. You should kill it, clean its stain, and prevent it from returning. Mold causes serious illness, including asthma, allergies, and lung infections.

  • Visually inspect the garage, and use a moisture meter to find mold growth areas
  • Fix leaks everywhere including the floor, door, windows and roof
  • Use insulation to prevent condensation in areas where warm and cool air meets
  • Wipe away surface water, and use a dehumidifier to remove moister to below 50%
  • Use a fan to speed up drying time
  • Wear skin, eye and air protection when searching for and cleaning mold
  • Replace drywall mold whenever possible because mold penetrates fibers that are hard to clean
  • Use a BAC or Quat (Wet & Forget or ShockWave) based products to clean garage wood, steel and concrete
  • Apply mold inhibitor (Concorbium) to the garage drywall, wood, plastic, concrete, stone and carpets
  • Use a hygrometer to test that he dehumidifier is maintaining garage air moisture below 50%

Bleach, vinegar, phenols (Lysol Disinfectant) and hydrogen peroxide have fungicidal properties, but are not as effective as the BAC and Quat chemicals.

Is Garage Mold Dangerous?

Mold in the garage is dangerous. The Centers for Disease Control (CDC) says that mold can cause infections in people with poor immune systems and chronic lung disease. Coming in contact with mold can cause a fever. Mold causes asthmatic attacks. Mold provokes allergic symptoms including red eyes, skin rash, sneezing, and a runny nose. The CDC says that the health response can happen immediately or sometime after the exposure.
Mold is also dangerous to clean. The CDC recommends wearing the following gear to clean garage mold:

  • long sleeve shirt
  • long pants
  • waterproof boots
  • goggles
  • rubber gloves
  • N-95 or better respirator

How to Find Mold in the Garage

Measuring wall moisture
Measuring wall moisture

Mold grows where there is water. Water enters the garage through leaks, porous concrete, and condensation. Use a moisture meter to find wetness.
Is rain seeping in through the garage seal? Then the garage door and nearby floor might be moldy.
Is there a big temperature difference between the garage and the outdoors? That difference can cause condensation, which shows up as water droplets on cold water pipes, for instance.
Does the garage floor have puddles? If you put a plastic food wrap on the floor over night, are there droplets on it in the morning? Then the floor might be moldy. Is there a carpeted floor mat on that weepy floor? Then the mat might be moldy.

Use a Moisture Meter to Find Excess Garage Moisture

Use a moisture meter to detect excess moisture on garage concrete, steel, wood and drywall.
A moisture meter tells you the moisture content of various materials. When shopping for a moisture meter, check that it works on garage materials you want to test. Some meters test drywall and concrete, some test wood, etc. This type of meter comes in “pin” and “non-pin” varieties. For pin measurements, put the pin on or in the material. For non-pin measurements, put the sensor on the material you want to measure.

General Tools Moisture Meter
General Tools Moisture Meter

Use a Hygrometer to Test Humidity

Keep the relative humidity in the garage below 50% to prevent mold growth. Some dehumidifiers come with built-in hygrometers, which are humidity testers. High humidity is a trigger to pull more moisture from the garage air.
You can start with a handheld hygrometer before purchasing a dehumidifier. If the relative humidity in your garage is always below 50%, you might not need to buy and run a garage dehumidifier.

LittleGood Hygrometer
LittleGood Hygrometer

Why is Mold Growing in Your Garage?

Mold is growing in your garage because there is water in your garage. Spores are common but don’t grow until they mix with water.
Spores are in your garage. That’s just a statistical fact. They come into the garage in the air, on your car, on equipment going in and out, and on your clothes.
You don’t see spores, but you can see and smell mold growth. Water is the magic potion that makes mold blossom.

How Long Before Garage Mold is Dangerous?

Mold is dangerous as soon as it starts growing. It starts growing one to two days after the spores and water meet. Young mold (mildew) releases spores that cause allergic, asthmatic and irritation reactions.
Never touch mold. Avoid breathing air in a moldy garage. This is where your personal protective equipment (PPE) comes in. You never want to touch, taste or breathe growing mold or its spores.

Where Does Mold Grow in the Garage?

Mold grows anywhere there is oxygen and moisture. Mold can grow on any surface in your garage. Mold grows on wood (walls, ceiling, and possibly the door), fiberglass (insulation), concrete (floor), steel (door), and drywall (walls).
Mold is common on garage walls, garage foundations, garage doors, and garage floors. Mold is slightly less like to grow on concrete, but it easily grows on minerals that fall onto the concrete floor. Do not confuse efflorescence for mold. Efflorescence is harmless salt, but it looks like a white mold common on concrete floors. Assume the worst until you’re sure one way or the other.

Is it Safe to Clean Garage Mold?

Cleaning mold is unsafe for people with compromised immune systems, asthma, and lung disease. Mold is toxic for everyone but particularly harmful to these groups. Otherwise, you can safely clean garage mold so long as you wear all of the protective gear. See the SBA mold remediation guide for a complete list. SBA recommends an N-100 respirator, and non-vented goggles.

Woman incorrectly cleaning mold on a wall.
This is NOT how to clean mold. She should be wearing googles and a mask. Mold is dangerous.

What is the Best Mold Cleaner for the Garage?

BAC (Wet & Forget), Quat (Shockwave) and Phenols (Lysol Disinfectant) are the best chemicals to kill and clean garage mold. Bleach, vinegar and hydrogen peroxide come in second place.

Wet & Forget and ShockWave (BAC and Quat) Mold Treatments

Benzalkonium chloride (BAC) and quaternary ammonium chloride (Quat) are from similar chemical groups that disinfect surfaces and kill mold.
Wet & Forget is a benzalkonium chloride (BAC), and ShockWave is a quaternary ammonium chloride (a Quat). These groups of chemicals are similar in nature and have varying abilities to kill different molds.
These chemicals work on wood, concrete and steel. While they do kill drywall mold, they can also kill the drywall during application. This is because BAC and Quat chemical applicators put a massive amount of water on the target. Unpainted drywall can absorb the water and disintegrate.
In any case, you need to dry that water out with a dehumidifier and fan to avoid creating more mold growths.
You always have the option of replacing that moldy drywall.

Fiberlock ShockWave
Fiberlock ShockWave

I have used Wet & Forget It on my home, deck, and ShelterLogic garage. I had a good experience with it in those places. For the attached home garage, though, you have to consider whether you can deeply wet a surface in order to kill the mold. You definitely do not want to add moisture to the garage with mold spores about. Too much water will break down unpainted drywall, so you don’t want to use this product there. If you use a water applicator in the garage, have a fan and dehumidifier ready to get the garage dry again.
Popular BAC mold treatments:

  • Wet & Forget Moss, Mold and Mildew Stain Remover
  • Mold Armor Disinfectant and Fungicide

Popular Quat mold treatments:

  • Fiberlock ShockWave

Phenol (Lysol Disinfectant) Mold Treatments

Phenol fungicides such as Lysol Disinfectant kill garage mold. Lysol outputs much less water than BAC and Quat treatments. This makes phenol-based treatments such as Lysol Disinfectant better for treating drywall.
Interestingly, Lysol Mold treatment is NOT as good for garage mold as is Lysol Disinfectant. Lysol Mold treatment is a bleach-based treatment more suited to the bathroom. Lysol specifically recommends NOT using this product on wood and painted surfaces.
While Lysol Disinfectant is good for killing many types of garage mold growth (see fungicide properties), it might or might not kill the mold in your garage. Lysol Disinfectant kills aspergillus niger. The label does not indicate that it kills other types of mold.
Phenols are toxic, but not overly wet like BACs, which makes phenols are better choice to kill garage mold. Not only is it essential you follow the directions for Lysol to work, you absolutely must wear the recommended inhaler when applying Lysol in large amounts.

Bleach, Tilex and RM-68 (Hypochlorite) Mold Treatments

Hypochlorite (bleach) fungicides such as RM-68 and Tilex are best at killing bathroom mold rather than garage mold. Bleach solutions and products depend on bleach’s ability to kill mold, and that ability is not absolute. Sometimes bleach appears to kill mold, but just knocks it dormant for a while.
Tilex does better in the bathroom where the surfaces are hard and non-porous. Bleach does not reach into unpainted wood and drywall the way that Phenol, BAC and Quat cleaners do.

Vinegar as a Mold Treatment

White vinegar is safe and effective at killing 80% of mold species. Vinegar of 5% or 6% acidity will kill mold growth if that growth is one of the 80% that vinegar can kill. If vinegar doesn’t work, you know it is in the 20%, and you will need a different approach.

Hydrogen Peroxide as a Mold Treatment

Hydrogen peroxide is a safe cleanser that removes mold growth stains from carpet, concrete, wood, drywall and steel. Fiberlock sells its peroxide product as a mold stain cleaner, not as a mold killer. While the hydrogen peroxide product has fungicidal (mold killing) properties, it’s better at cleaning the dead mold then killing it in the first place.
Popular peroxide mold cleaners:

  • Fiberlock Advanced Peroxide Cleaner

How to Remove Mold from the Garage

Use this mold remediation guide from SPB, formerly known as St. Bernard’s Parish, which is a charity that grew out of Hurricane Katrina disaster recovery. This is the most complete and thoughtful mold remediation guide I have found. The guide outlines the personal protection equipment (PPE) you should wear, and the steps you should take to remove mold from the garage.

Wear Safety Equipment to Clean Garage Mold

First, protect yourself. Protect your skin, your eyes, and your airways. Wear long clothes, rubber gloves, and a respirator.

Find and Fix Garage Leaks, Condensation, and Humidity

Next, use a moisture meter to find areas of areas of excess moisture. Excess moisture comes from leaks and condensation.

Insert pins into wood to get internal moisture measurement
Insert pins into wood to get internal moisture measurement

Fix all leaks, whether they are in the garage door seal, the roof’s gutter, or the windows. Use insulation on condensation areas such as sweaty pipes. Condensation occurs when cold and warm air meets.
Dry wet areas with towels and run a fan to speed up the process. Use a hygrometer to test relative humidity. Run a dehumidifier to reduce air moisture below 50%.

Kill the Garage Mold

Use a fungicide to kill the mold. After waiting the recommended time, brush the dead mold with a wire rather than a nylon brush. Wearing your respirator is literally critical at this stage. Flaking moldy drywall into the air is an invitation for lung disease.

Wear personal protective equipment when spraying mold
Wear personal protective equipment when spraying mold

Clean the Garge Mold Stain

Use a HEPA vacuum to clean the loosened particles. HEPA filters grab tiny particles that lesser vacuums shoot back into the air. Any live spore shooting back into the garage is another mold spot giving birth. Just add water.
When everything is dry, apply a mold inhibitor the garage surfaces.

Concrobium mold inhibitor
Concrobium mold inhibitor

Sanitize Your Mold Cleanup Safety Gear

Clean the clothing and protective gear after use. Wash clothing in bleach and hot water, or soak it in Fiberlock Advanced Peroxide Cleaner. Spray goggles with Lysol Disinfectant. Allow time for the product to kill any mold, and then wash the goggles in hot, soapy water.

How to Remove Mold from Garage Walls and Doors

Use Fiberlock ShockWave on wood walls, and wood or steel doors. Run a dehumidifier and fan during and after treatment. Use a steel brush and a HEPA vacuum to loosen and remove dead mold.

Measuring moisture at stairs with Tramex MEP moisture meter
Measuring moisture at stairs with Tramex MEP moisture meter

How to Remove Mold from Garage Drywall

If the drywall in your garage is unpainted, cut out the affected piece and replace it. Drywall is soft. Mold eats the outer layer, and then digs into the inner fibers. Bleach does not get into fibers.
BAC and Quat treatments reach the fibers, but the treatment can waterlog the material. Benzalkonium chloride treatments are best at killing deep mold partly because you apply them with a lot of water. The water carries the fungicide to the interior fibers. But that is counterproductive, because wetting down unpainted drywall will just destroy it. You have to burn the village in order to save it.
Even professionals who advocate bleach admit that bleach-based mold cleaners are not effective below the surface. You can scrub a bleach solution into the drywall. If the affected area is just on the surface, the bleach might be effective.
Never paint over mold. Paint does not stop mold growth.

Measuring wall moisture
Measuring wall moisture

How to Remove Mold from the Garage Floor

Make sure that the white powder on the garage floor is mold and not efflorescence. Wearing goggles and a respirator, use a magnifying glass on the garage floor. Efflorescence is a harmless salt that rises to the surface from under the concrete. You can use a broom to sweep it away. Mold sticks to the floor and does not move under a broom.
Concrete grows mold because it is naturally porous and moist. Material such as minerals and dust fall on concrete, and the materials can get moldy. In this case, a broom might move the moldy material along. If you cannot tell if it’s mold, assume it is mold and clean it wearing protective gear, including an N-95 or N-100 respirator.
If a carpeted floor mat is moldy, consider throwing it out. Mold penetrates fiber and the infiltration can be hard to remove. You can clean fiber mold with Fiberlock Advanced Peroxide Cleaner.

How to Permanently Remove Garage Mold

You cannot permanently remove mold spores from the garage, but you can prevent leaks, condensation, and excess humidity.
Even mold remediation professionals do not guarantee permanent mold removal. Once mold is in a building, it’s next to impossible to track it all down and kill it. Spores fly through the air, evading your steel brush and fungicide.
As a result, your focus should be on:

  • killing the mold
  • removing the stains
  • ensuring the garage is and stays dry to prevent future growth

Keep the garage humidity below 50%. Use a fan to dry moisture. Wipe down wet spots. Insulate pipes, walls and the door to prevent condensation. Run a dehumidifier to collect water out of the air. Empty the tank often, or drain the water to the outside.

The Great Bleach Debate

Bleach solutions work well to clean bathroom mold because bleach works well on hard tile. Bleach is less effective on softer wood and drywall, and porous concrete. You can learn more about where U.S. government agencies stand on the matter below.

Mold References

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