How To Get Rid of Mold in Basement (*Ultimate Guide*)

Do you want to know how to get rid of mold in a basement?

Mold grows in basements as a result of excess moisture, and unfortunately --- it is a common experience with underground basements.

In this guide, I will go over...

  • How to get rid of mold in a basement
  • The most common causes of excessive basement moisture
  • Equipment needed to clean mold
  • Simple measures to prevent mold from regrowing

Let's get started with this guide!

how to get rid of mold in basement

How To Remove Black Mold In A Basement?

In addition to addressing the causes of moisture in a basement, if you have visible mold, it is important to begin the mold removal process.

If the mold is extensive, hiring an experienced contractor is strongly recommended. With a large mold contamination, full hazmat suits, face masks, air blowers, and other equipment may be used to remove and contain the mold.

My recommendations for mold removal are for small areas of mold growth only such as less than 10 square feet.

Ventilate The Area While Cleaning

It's important to realize that mold removal may release spores throughout the home if it is done in a haphazard way. It's a good idea to ventilate the home as much as possible during the mold remediation process such as opening windows.

Be careful in using the HVAC system to ventilate the home because it may blow mold spores throughout the home (especially if there is mold growth in the furnace as well).

Some equipment you may want to use when removing mold include face masks, gloves, high quality trash bags, goggles (without vent holes), and a spray bottle.

Read Also: What Are The Signs of Black Mold in Air Vents?

Removing Drywall And Carpet

If you mold growing on drywall or carpet, and you can't just wipe it off (mildew), then you really should just cut it out. (To know the species of mold you are dealing with, there are also mold test kits for homeowners that you can purchase.)

Mildew is usually powdery and just surface coats drywall and carpet which can be easily wiped off. Mold however will grow deeper into drywall and you can't just clean it or paint it over.

Drywall Removal

Before you start cutting and removing drywall, you may want to spray it down with water to help prevent spores from being released into the air.

It is also a good idea to turn off the HVAC system so mold spores don't get spread throughout the entire home. Mold spores are only released when the material is agitated such as removing cutting and removing drywall.

Depending on the size of the mold contamination, you may even want to section off other rooms with plastic sheeting --- but this begins to get into the realm of professional removal.

As soon as you remove the drywall, place it in a trash bag, and take it outside. If there is any insulation inside the wall that has black mold growth, it also should be removed.

Cleaning Wood Framing

After you have removed any contaminated drywall, it's important to get a flashlight and closely inspect the wall framing (studs).

If there is any visible mold growing on the wood, it will have to be cleaned and sanitized --- and you may have to remove more drywall just for access. Before attempting to clean mold from wood framing, be certain that there isn't any deteriorated or rotted wood.

If any of the wood is deteriorated, it will have to be replaced. Having a qualified contractor to help with framing repair is highly recommended.

Killing Black Mold With Sanitizing Spray

If there is no rotted wood, then the first step is to kill the mold by spraying it with a bleach and water solution --- however, if spraying a large area bleach can irritate your lungs. A 1 part bleach to 9 parts water solution is recommended (10% bleach).

For larger areas, you may want to purchase a specialized sanitizing spray made for killing mold. 

Let the cleaning solution soak the mold for at least 15 minutes, then dry it off.

Kilz Sealer

Before re-installing drywall, you now want to seal the framing --- I always recommend using Kilz sealer. Kilz has fungicidal properties and will help prevent any residual mold spores from regrowing --- it comes in gallon/quart buckets as well as spray paint.

How To Lower The Basement Humidity?

If you have visible mold in the basement, one of the first things I would do to check the relative humidity level. It is almost impossible for mold to grow if the relative humidity is below 60% (ideally between 30% to 50%).

Humidistat

You can buy a simple $10 humidistat to check the indoor humidity. During the mold remediation process (and treating the causes), I want to monitor the humidity levels.

Dehumidifier

If the basement humidity is above 50 to 60%, the first thing I would do is install a cheap dehumidifier to get the humidity down.

Most dehumidifiers you can even connect a water tube and insert it into a sink or tub so you don't have to keep dumping out the water tank.

Moisture Meter

Even if the basement humidity is below 60%, the exterior walls may have very high moisture levels.

You can buy a moisture meter for $25 to $50 and it is a valuable tool for diagnosing moisture problems. With a drywall moisture meter, you can quickly go over the entire basement, and determine any areas with high moisture levels.

The most common areas of high moisture are the basement corners --- and of course, it's related to downspouts dumping hundreds of gallons of water right next to the foundation.

I invite you to check out my detailed review on the best moisture meters to find hidden sources of water.

Bathroom Exhaust Fans

If there is a full bathroom in the basement, it is important to make sure that the home occupants actually use the bath fan.

I did an inspection for a home once where mold was growing along a basement hallway, and right next to this area was a bathroom.

Well, guess what? The bathroom did not have a bathroom fan. Any humidity from showering is all released into the basement. This is a big problem.

Should I Inspect The Furnace?

During the mold removal process, I highly recommend that you take off the cover to your furnace or indoor air handler to inspect for mold.

Since mold spores can travel throughout the entire home, the interior air handler is a central location where I commonly find mold growth. The air handler has three things going for it that mold loves... dust, darkness, and moisture.

Most covers are easily removed with a few screws or a few latches. Carefully inspect the blower fan, the ducting, and the evaporator coil for any signs of mold.

If there is mold growth in the furnace, it must be cleaned. Hiring an air duct cleaning company to clean the furnace (and air ducts) is recommended.

steam vs evaporative whole house humidifier

Read Also: 7 Pictures of Mold in Air Ducts (What It Looks Like?)

HVAC Filter

After you remove the basement mold, and clean the furnace, it's important to stay up to date on your HVAC filter installations. Most HVAC filters say that they are good for 3 months, but I always recommend to my clients to change the filter every 30 days.

Should I Install An HVAC Ultraviolet Light?

When the entire mold removal process is finished (including the furnace), then installing an HVAC UV light is highly advisable.

Here is an article I wrote on my best picks for HVAC UV lights to kill mold.

An HVAC UV light is a special type of light bulb that is installed inside your furnace, and it shines 24-hours to kill and prevent mold growth. The UV light shines a special light frequency known as UV-C that has been proven to kill mold organisms.

It actually disrupts their cellular DNA. Hospitals have been using UV lights for years to sanitize operating rooms.

The Worst Moldy Basement I Have Ever Seen

During my years as a home inspector (as well as a real estate investor), I have seen many basements with horrible mold growth.

I remember one inspection I performed on a home, mold was growing everywhere in the basement. Black mold was growing on the floor (through the wood flooring), and all over the walls and ceilings (drywall). Mold was likely growing inside the wall cavities on the wood studs.

Unfortunately, I didn't take any pictures on this inspection, since I was primarily doing air quality testing for insurance purposes (and yes, it tested very positive for mold).

On this home, the whole basement would have to be demolished and completely refinished --- likely to cost in the $40k to $50k range. Fortunately, most mold growth isn't this bad.

With this unfortunate homeowner, he vacationed in Africa for two months during the heat of summer, and he made two serious mistakes.

  1. He turned off the A/C
  2. He didn't turn off the main water line (and drain the plumbing) because the water heater sprung a leak

Most people don't realize that the air conditioner also has a dehumidifying effect, so even with the leaking water heater (not that bad of a leak), the mold likely wouldn't of taken root so extensively.

Read Also: How To Prevent Mold in Air Conditioners?

The Most Common Causes of Basement Water

If you have mold in the basement, at the same time as you clean or remove it --- it's also important to focus on the cause.

I will discuss some of the most common causes of excess water or moisture in an underground basement.

Poor Water Management

The hands down #1 way that water or moisture goes into a basement is from poor exterior water management.

The average roof has a significant amount of surface area, let's say around 1500 square feet. If the average rainfall in your state is in the 30-40 inch range, then that means your roof drains thousands of gallons of water every year onto the ground.

That is a lot of water!

And the basement wall doesn't have to become saturated with water for mold or mildew to grow. If there is enough humidity in the air, such as above 60% relative humidity, mold can grow just from the dampness.

Gutters And Downspouts

Almost every single home inspection I perform, I recommend to my clients to install downspout extensions to drain water farther away from the home.

It's such a simple thing to do, but it's also very important --- especially with basement mold or water issues. Install extensions on all downspouts, and make sure the water is properly draining several feet away from the home.

The next time there is a rain storm, it would be valuable to see how water is draining next to your home.

Is water ponding in certain areas? Are the gutters and downspouts actually working to divert water away from the home?

sources of basement water

Landscaping (Grading)

Another extremely common recommendation that I give to my clients is to improve the grading.

Grading is term used in the real estate industry for the slope of the lot. Usually, when I perform inspections, the ground is either flat, and in some areas --- even sloping towards the home.

You always want the ground next to the foundation to slope downwards and away from the home. Ideally, the ground should gradually slope downwards at least seven inches for the first seven feet from the foundation.

Proper home grading is building practice that has been in use for probably thousands of years --- it is hardly a new discovery.

Wall Penetrations (Pipes, Cables, & Vents)

Besides the gutter/downspout drainage system, and proper home grading --- the third most common source of water is the wall penetrations.

Basically, I am referring to any pipe, cable, or vent that is penetrating the exterior wall. And on some houses, there are a lot of holes.

This is necessary of course, since we have dryer vent (and bath) covers, gas meters, power meters, exterior A/C condensers, and other objects that need to go through the wall.

But, quite often, where these pipes go through the wall, it isn't properly sealed.

hose bib allowing water into basement

So especially if you are having moisture issues in a certain area of the basement, I would carefully look on the outside wall if there are certain things going into the wall that aren't sealed.

Sometimes it is objects that you wouldn't expect such as a deck. If a deck is bolted through the home, and flashing isn't used, or it isn't installed properly, moisture can form inside the wall.

Make sure all wall penetrations are thoroughly sealed with exterior caulking or plumber's putty.

Read Also: Should I Get A Mold Inspection When Buying A House?

Mold Growth Needs Three Things

Mold needs three things to grow in any environment...

1. Food Source

The food source for mold in a basement can be the gypsum drywall, paper (on the back of the drywall), carpeting, carpet pad, wood studs (framing), and other cellulose objects.

I discover mold in basements most commonly on drywall.

2. Water Source

Mold will be inactive unless it has a water source. With basement problems, the water is usually from the exterior, but sometimes there can be interior plumbing leaks.

3. Darkness

Mold can't grow in direct sunlight.  Unfortunately, most basements don't receive a lot of sunlight. Especially if you go on vacation, mold may take root in the basement.

What's The Bottom Line?

If you have visible mold in your basement, it's something to take seriously for the sake of your health.

You want to attack basement mold on two fronts. It's important to quickly and effectively remove any visible mold. You will have approximately 24-48 hours to clean any water saturated material in a basement before mold growth may appear --- acting quickly is a priority.

But at the same time, you want to remove the cause of the mold. Mold cannot grow unless there is some type of water source... either liquid water or very high humidity.

I hope you enjoyed my article. If you have any questions or comments, please leave it at the bottom of this article in the comment box --- I promise to answer all questions. Thank you.

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Arie Van Tuijl

Arie Van Tuijl

Arie is the founder of Home Inspector Secrets, an online resource dedicated to helping people understand how homes work. He is a licensed home inspector in two U.S states and owns a residential and commercial inspection company. To ask Arie a question, please use the comment box at the bottom of the relevant article.

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