How to Remove Mold From a Plywood Subfloor: 10 Must-Do Steps

By: Diana Rodriguez-Zaba
Updated on: November 2, 2020

Damp subflooring doesn’t turn into a cleanup project overnight. Whether it was soaked during storm flooding or saturated after an apartment plumbing mishap, a wet subfloor eventually becomes moldy.

How do you handle mold on the subfloor in the kitchen? How do you get rid of mold in the bathroom under the flooring?

Our ServiceMaster Chicago team explains how to remove mold from plywood subflooring in every room.

Let’s get started.

How to Treat Mold on a Plywood Subfloor: Your 10-Step Guide

The signs of mold under hardwood floors, carpets and vinyl are usually the same. You notice dark patches on the floor or a musty smell throughout the room. You pull up a small corner of flooring and expose the problem.

You’re looking at a big DIY project. Start by making sure you’ve taken care of the moisture source, and then follow these 10 steps for cleaning mold from a plywood subfloor.

black mold on wall

1. Protect Yourself First

Exposure to mold can result in serious health problems. Protect yourself by wearing an OSHA-approved particle mask or respirator. You also need a supply of disposable gloves, shoe covers and throwaway clothes.

Power Tip: Walking through the house in your work gear spreads mold spores, so keep a change of clean clothes just outside the affected area.

2. Check the Room’s Contents

Check furnishings and items in the room for signs of mold. Pay special attention to throw rugs, the bottom of table and chair legs and any other surfaces that rest directly on the floor. Double-bag and throw away anything that appears contaminated, and move everything else to a safe place.

3. Secure the Working Space

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.

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

4. Remove and Inspect 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.

5. 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.

6. Treat the Molded Plywood

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 plywood. 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 plywood.

7. 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.

8. Clean Up Any Remaining Mold

If there are areas of dead mold still left on the subfloor, try removing them with a HEPA vacuum. You can also give the plywood a final scrub using your treatment solution and disposable rags.

9. Treat Once More and Dry

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

10. 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.

We Want You to Be Safe

mold remediation professional

We must stress the importance of personal safety when you tackle mold growing in your home’s subflooring. The work can have a negative effect on your health and impact family members who deal with respiratory problems.

If you have any doubts about doing it yourself, please contact us first. Our mold remediation professionals  in Chicago are industry certified and highly experienced. You want the city’s most trusted mold removal specialists, so give us a call here at ServiceMaster by Zaba.

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.