How to Identify and Treat Mold in Your Basement

By
Lee Wallender
Lee Wallender
Lee Wallender

Lee has over two decades of hands-on experience remodeling, fixing, and improving homes, and has been providing home improvement advice for over 13 years.

Learn more about The Spruce's Editorial Process
Updated on 06/06/22
Fact checked by
Sarah Scott
SS
Fact checked by Sarah Scott
Sarah Scott is a fact-checker and researcher who has worked in the custom home building industry in sales, marketing, and design.
Learn more about The Spruce's Editorial Process
Treating Mold in Basement

yavdat / Getty Images

Project Overview
  • Working Time: 3 - 4 hrs
  • Total Time: 3 - 4 days
  • Yield: 80 square feet of basement wall
  • Skill Level: Beginner
  • Estimated Cost: $30 to $60

If any place in the house will grow mold, it's the basement. Basements collect and trap moisture, and moisture is one factor that leads to mold growth. And because basements have less natural light and airflow than other parts of the home, that mold will not die off on its own. Some strains of black mold can be a health hazard. Plus, mold can quickly decay organic materials such as wood, leading to structural failure. This means that identifying and treating mold in the basement should be a priority as soon as you believe that you have it.

Mold in the Basement: Identifying and Treating It

Homes that have basements often have mold. Due to basements' proximity to groundwater, water can wick up through concrete floors and continue wicking up through floor sleepers and wall studs. Homes without a robust water diversion system may accumulate water in the soil that can crack the foundation, which results in water leakage.

Identifying and treating basement mold is a multi-stage process. You must find the mold, then test it to make sure of what you're dealing with. You'll remove structural elements to permit access to the mold, as needed, and go through the process of killing the mold. Then you'll mechanically remove or encapsulate the dead mold spores, depending upon which is best for your situation. Finally, you'll turn your attention to fixing the problem that allowed the mold to grow in the first place.

Codes, Regulations, and Permits

Most communities do not have laws that monitor mold or enforce mold removal. However, always check with your local permitting office to see if permits are required for mold removal.

When to Treat Mold in the Basement

Remove mold in the basement as soon as possible to prevent its further growth. If the basement has recently been flooded, first remove all of the water and wait until the basement is completely dry before you begin removing the mold.

Safety Considerations

Because some strains of mold can be hazardous, wear the full range of personal protective equipment and seal off the work area. The personal protective equipment includes a HEPA N95 mask at a minimum, but ideally a P100 mask, hooded disposable coveralls, latex or latex-substitute gloves, shoe covers, and safety glasses.

The 5 Best Mold Removers of 2023

What You'll Need

Equipment / Tools

  • Cotton swabs
  • Glass container
  • Work light
  • Screwdriver
  • Wet/dry vacuum
  • Sponge
  • Personal protective equipment

Materials

  • Household bleach
  • Garbage bags
  • Plastic sheeting
  • Duct tape
  • Mold remover spray

Instructions

How to Identify Mold in the Basement

  1. Smell the Air for Mold

    One of the first indicators that your basement has mold is its smell. Mold is variously described as smelling musty, dusty, or earthy. If you know the smell of wet wood or dirty socks, this is similar to the smell of basement mold.

  2. Identify Areas Known to Harbor Mold

    When you believe you smell mold, go on the hunt to find it. Look near water supply pipes, around water drainage lines and sewage pipes, anywhere near dryer vents and in laundry rooms, under sinks, in the ceiling above a finished basement, near bathroom exhaust vents, around sump pumps, and inside wall cavities.

  3. Visually Locate the Mold

    Turn on the work light. Scan for signs of mold, including small black speckles, areas that look like burn marks, or large areas that simply look dirty.

  4. Test For Mold With Bleach

    Add 1 part bleach to 10 parts water in the glass container. Mix it well and daub the cotton swab in the mixture. Run the swab across the area suspected of mold. If the surface is dirty, the mixture will not cause it to change colors. If it is mold or mildew, the swabbed area will lighten.

  5. Probe the Area

    With the screwdriver, gently push into drywall or wood areas of suspected mold. If it is mold, the screwdriver will easily push into the surface, flaking it away. Sometimes, the material will fall apart.

How to Treat Mold in Your Basement

  1. Prepare the Work Area

    Ventilate the room with a box fan with the airflow moving toward the exterior. Tape plastic around the work area. Turn off the HVAC system or furnace to avoid carrying mold spores throughout the rest of the house.

  2. Dry the Work Area

    Use the wet/dry vacuum to vacuum up water. For other latent moisture, increase the heat in the room, turn on dehumidifiers, and leave the fan running until the area is completely dry.

  3. Spray the Mold With Mold Remover

    Spray down the areas of basement mold with the mold remover. Wipe the mold remover across the surface with the sponge, thoroughly working it in.

  4. Clean or Encapsulate the Mold

    After the mold remover has dried, the mold spores are dead but the mold physically remains. You may choose to paint over the mold with an encapsulating product designed for this purpose or remove the mold with dish detergent and hot water.

    Tip

    Surfaces such as bare drywall that can be ruined by the application of too much water should be encapsulated with with a mold sealant product for ongoing protection rather than cleaned with water.

  5. Prevent the Mold From Growing Again

    A good system of gutters and downspouts is one step toward reducing basement moisture. Grade soil around the home downward. Dehumidifiers in the basement can reduce the moisture content in the air. Seal around dryer vents with metal tape. Check pipes for leaks and fix, as needed.

When to Call a Professional

Mold remediation companies can treat basement mold, especially if you have large, pervasive sections of mold. If you are proceeding with a real estate sale, you may be contractually required to have a professional mold remediation company remove the mold rather than you treating it by yourself.

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The Spruce uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

  1. Borchers AT, Chang C, Eric Gershwin M. Mold and Human Health: a Reality Check. Clin Rev Allergy Immunol., vol. 52, no. 3, pp. 305-322, 2017. doi:10.1007/s12016-017-8601-z

  2. Who Can Test My Home or Clean, Fix, and Remediate My Home for Mold? United States Environmental Protection Agency.