How To Get Rid Of Mold From Subfloor: 8 Steps

By: Diana Rodriguez-Zaba
Updated on: March 28, 2024

If you have mold in your subfloor, you have to act quickly to remove it.

In addition to being a health hazard, mold can destroy your flooring and lead to costly and extensive repairs.

Fortunately, we’re here to help.

At ServiceMaster Restoration by Zaba, we have more than 85 years of combined experience eliminating mold from subfloors, and we’ve compiled that expertise into this complete guide.

Before You Get Started

Do these things to set yourself up for mold removal success:

  • Prioritize your safety. When addressing mold in your subfloor, it is crucial to wear appropriate personal protective gear (PPE) to safeguard your health. This includes an N-95 or N-99 face mask to filter out mold spores, disposable gloves to prevent direct contact with mold, shoe covers and hair covers to prevent spreading mold spores to other areas, and long pants and long sleeves to protect your skin from potential irritants. It is also important to set up a “negative pressure environment,” since it can prevent mold spores from spreading to other areas of the home. You can do this by using an air filtration device to create a vacuum effect – directing airflow away from the contaminated space without allowing contaminated air to escape back into clean areas.
  • Consider your treatment options. If you have mold in your subfloor, there are several treatment options available, and each varies in approach and effectiveness. For minor mold issues, cleaning the area with mold-killing solutions such as vinegar or bleach may suffice. For more severe infestations, however, you’ll need to use stronger methods. This might include replacing affected wood panels or applying specialized mold remediation products that penetrate surfaces to eradicate mold at its source. 
  • Decide between DIY and professional removal. DIY mold removal methods can be effective for small, visible areas of mold. If the infestation is more widespread, though, professional removal is strongly advised. Professionals have the equipment, chemicals, and expertise needed to safely and thoroughly get rid of mold, even in areas where you can’t see it with the naked eye. They also conduct air quality tests to ensure the environment is safe post-removal, which is usually beyond the scope of DIY efforts.

What Causes Mold To Form In Subfloor?

mold in subfloor

When mold forms in subfloor material, it can be due to any of the following causes:

  • Moisture Accumulation: Persistent moisture, whether from spills, high humidity, or leakage, provides the ideal environment for mold growth.
  • Lack of Proper Ventilation: Inadequate ventilation in crawl spaces or basements contributes to stagnant air and moisture buildup.
  • Water Leaks: Leakage from pipes or appliances situated above or around the subflooring can seep down and create a moist environment conducive to mold.
  • Flooding: Events like flooding can saturate subfloor materials, and if not dried out properly, can lead to mold development.
  • Condensation: Cold surfaces beneath floors can lead to condensation, especially if there’s a significant temperature difference, providing another moisture source for mold.
  • Poor Drainage: Exterior poor drainage systems can cause water to pool around a home’s foundation, potentially seeping into subfloor components.

How To Treat Mold On A Subfloor: Your 8-Step Guide

how to treat mold on a subfloor

1. Determine The Cause

To determine the cause of mold in your subfloor, start by examining areas that are prone to moisture buildup, since mold thrives in damp environments. 

Here are a few tips:

  • Look for signs of water leaks, such as stains or discolorations on the flooring or nearby walls. Pay special attention to plumbing fixtures, inspecting for any leaky pipes or fittings that might be introducing moisture into the subfloor. 
  • Check the exterior of your home as well, ensuring that downspouts and gutters are directing water away from the foundation. 
  • Utilize a moisture meter to pinpoint areas with excessive moisture levels. 

Once you’ve identified a cause, such as a burst pipe or a leak, you’ll need to address and resolve this source of moisture promptly. Addressing the root cause not only halts the spread of mold but also prevents future occurrences.

2. Secure Your Workspace

Secure the room by hanging heavy plastic sheets over doors, windows, air registers and vents. Leave one window open so that you can blow contaminated air outside. Position a heavy fan to vent out the window, and let it run constantly while you work.

Be careful to angle the fan so that it doesn’t blow directly on the moldy subfloor.

Additionally, consider shutting down your HVAC system during mold removal. 

Here’s why:

The airflow generated by HVAC systems can easily distribute mold spores to other areas of your house, contaminating clean spaces and causing other issues like allergies and respiratory problems. 

By turning off the system, you effectively minimize the risk of cross-contamination, ensuring that the mold removal process is thorough and limits mold’s impact on your home’s indoor air quality and your health.

3. Locate The Mold

Once you’ve secured the area and pinpointed the source of the moisture that’s allowing mold to grow, you’ll need to identify the mold itself.

Here’s how to do it:

  • Look for Visible Signs: Begin your inspection by looking for visible signs of mold. Mold can appear as fuzzy, slimy, or powdery and often in shades of black, green, white, or yellow.
  • Identify Mold by Smell: Mold has a distinctive musty, earthy smell. If there’s a strong odor, it’s likely there’s mold growth, even if it’s not immediately visible.
  • Remove Baseboards: Carefully pry baseboards away from the wall, and inspect them for any signs of damage. Subflooring mold often spreads to trim, so you’ll probably have to replace the old baseboards. Double-bag and dispose of mold-damaged trim.
  • Use a Flashlight: Shine a flashlight at an angle against the subfloor. This technique can help reveal mold growth that might not be visible with overhead lighting.

4. Expose The Moldy Subfloor

Depending on the type of floor in the room, use one of these techniques to remove it and any underlayment. You need to completely expose all moldy subflooring.

  • Pry up hardwood floors one board at a time starting at one edge of the room.
  • Pull back and tear out carpet and padding, and pry up tack boards.
  • Cut slits in linoleum floors in the bathroom or kitchen, and scrape up flooring and backing.
  • To safely dispose of contaminated material, seal it in heavy-duty plastic bags. Check local regulations for disposal of mold-infested materials, as some areas may require special handling or dropping off at designated facilities.

5. Treat The Molded Subfloor

Treat exposed molded subflooring with a mixture of 1 cup of borax and 1 gallon of water or an EPA-registered mold removal product. Spray the solution on the moldy subfloor. You can also soak affected subflooring with a brush broom. Wait 10 minutes, scrub the area, and repeat the process two more times.

Power Tip: Repeated applications allow a treatment to penetrate and kill mold deep in the subfloor.

6. Check Floor Joists

Mold in a subfloor can spread to floor joists, so take a look down in the crawl space. If you find signs of mold, treat the entire area. Otherwise, mold will spread back into your subflooring.

7. Treat Once More And Dry

After you’ve removed all mold from the subfloor, lightly coat it with a fresh layer of treatment solution, and let everything dry for three days. Use large fans and a dehumidifier to speed up the process.

8. Repair And Replace Damaged Subflooring

You may find that some subflooring needs repair or replacement. This adds more time and elbow grease to the job, but you know your subfloor should stay in good shape for years to come. Finish up by replacing the carpet, hardwood or vinyl, and congratulate yourself for taking care of a very big project.

Let Us Help You Get Rid Of Mold Safely And Effectively

mold removal

Mold removal can be a complex, exhausting, and dangerous process.

Fortunately, you don’t have to do it alone.

Regardless of why you have mold in your subfloor, our team can help you get rid of it. 

Offering comprehensive water damage restoration and mold removal services, we’re here for you.

Contact us today to learn more about us or request your quote. 

How do you check for mold in a subfloor?

Pay attention to strong, musty smells. Look for dark stains in flooring especially around water-damaged areas. Pull up several floorboards or a 1-foot square of carpet and padding. Use a flashlight to inspect the subfloor for signs of mold.

How do you treat mold on a subfloor?

Expose the subfloor by pulling up carpet or floorboards. Mix 1 gallon of water with 1 cup of borax, and spray the solution on the moldy subfloor. Let it sit for 10 minutes, and scrub clean. Repeat the process twice.

How do you remove black mold from a subfloor?

Don’t risk your health by trying to clean toxic black mold from a subfloor. Leave the job to certified mold removal technicians. They eliminate toxic mold using industry-proven remediation techniques that prevent its return. They also repair and restore affected subfloors, flooring, baseboards and drywall.