How to Kill Mold on a Wood Subfloor

Hunker may earn compensation through affiliate links in this story.
If you have damp subflooring that has turned moldy, then you should know that this isn't a simple cleanup job.
Image Credit: SrdjanPav/iStock/GettyImages

If you have damp subflooring that has turned moldy, then you should know that this isn't a simple cleanup job. Although you can clean up mold yourself, it's not a easy task to kill mold on a wood subfloor. Not only are you dealing with treating the mold, but sometimes it's difficult even to see signs of mold under hardwood floors. If you detect mold on plywood subfloor, then you should really hire a professional to get the job cleared up.

What is Sub-flooring?

Sub-flooring is the layer or layers of flooring that is underneath a finished floor covering. A finished flooring can be made out of carpet and pad, hardwood, laminate, vinyl or ceramic tile, and they're usually the layer on top of floor joists. If you have a vinyl or sheet vinyl flooring, then you may have more than one layer of subflooring.

The majority of subflooring is made out of plywood or oriented strand board (OSB), which is a type of engineered wood. Since most sub-flooring is made out of plywood, it is highly susceptible to mold.

How Does Mold Develop?

Unfortunately, it doesn't take much for mold to grow, and with subflooring, it can go undetected for long periods. Since there are layers of flooring, mold can be stuck between those layers. Mold in subflooring can form for a variety of reasons. If you have a leaky faucet, then it can build there.

Also, if there is excess subfloor moisture, mold is more apt to grow. In warm homes, mold is also more likely to develop. The combination of warm temperatures, water and materials like plywood or OSB is a recipe for a mold disaster.

Mold Health Risks

Although mold may seem like public enemy number one, it's actually everywhere. You just have to keep an eye out for the type and amount of mold that is in your environment. Mold is in nature and even in our homes, but if mold growth is visible to the naked eye, that's when you know that you have a problem.

Mold colonies reproduce or are attacked by different types of mold colonies. If mold spores or mycotoxins (chemicals present in the mold) are released into the air and inhaled, then this can cause allergic reactions in people that have sensitivities to mold. If you come into contact with mold, it can cause nasal stuffiness, throat irritation, coughing or wheezing, eye irritation, skin irritation or severe allergic reactions.

If you have chronic lung illnesses, you can also get severe infections in your lungs due to being exposed to mold. If you do have a chronic lung illness, then you should stay away from compost piles, cut grass and heavily wooded areas.

Signs of Mold Under Hardwood Floors

If mold is growing underneath your floorboards, then it can be a bit challenging to detect initially. For the most part, you should see mold. But if mold is growing underneath finished sub-flooring, you won't usually see it..

You can smell it, though. If you're smelling a musty, pungent, earthy odor, then you might have mold.

The easiest way to detect mold in sub-flooring is if you see discoloration, warping or distortion in areas of flooring. Plywood and OSB absorb moisture, so this can cause their layers to separate or warp. But mold under vinyl plank flooring can even grow. When you see warping, it may not be a 100 percent chance you have mold, although it can be a strong indicator that you have a problem.

If you're suspecting mold because you see that your sub-flooring is warping, or your carpet and pad roll back easily, you need to inspect your sub-flooring further. To detect mold in plywood sub-flooring, you're going to have to remove a small area and check underneath. You can reinstall hardwood or plywood easily, and it won't cause damage to the overall flooring.

Mold Removal Myths

The cleaning rumor that bleach can always kill mold is, in fact, not true. It actually won't kill mold that is on porous surfaces. Chlorine bleach is only made out of 95 percent water and 5 percent chlorine. Chlorine does kill bacteria, but it's not strong enough to kill something as powerful as mold.

If you apply chlorine to the wood sub-flooring, all it will do is absorb into the wood because wood is very porous. Chlorine doesn't absorb into porous materials, but because chlorine only compromises about 5 percent of the overall solution, that little bit will only clean the surface mold. The mold that is under the sub-flooring, which is what's causing the real problem, won't be absorbed.

Bleach can kill mold, though, that is on non-porous surface materials, such as glass, countertops and ceramic tile. To kill sub-flooring mold, you can clean it on your own. It is recommended that you hire a professional to make sure that every bit of mold is killed.

Professional Mold Removal Tips

If you get an inspection and they suspect that there is mold, the area has to be covered and cleaned immediately. If the area isn't covered, the mold can spread through mold spores. Trying to remove subfloor mold is a bit of a complicated process. If you don't know what you're doing, then you can spread the mold to unaffected areas in your household.

You need a plan to contain and remove the mold before you actually begin the removal process. If you hire out workers, then they will have all of the equipment that you'll need to remove the mold, and they're well-versed in these jobs. First, they'll have a negative air machine:or air scrubber to scrub any of the mold spores from the air. This will also prevent cross-contamination. They'll also use protective equipment such as masks, gloves, and unique clothing when they're dealing with the mold infestation.

Mold Removal Aftercare Tips

Aftercare is just as important to mold pre-prep and the removal process. If any porous materials come into contact with the mold, then they may be contaminated. This means you'll have to remove and discard these items, as well. A mold removal crew will make sure that any additional materials aren't affected, as well as make sure that the mold will not reappear.

They will also make sure any extra water is cleaned up because even though mold will not survive without water, mold spores can actually reform. If the mold spores reform, then your mold problem will return. That's why you must have professionals clear away every bit of the mold. You may think that you have gotten rid of the mold, but it can come back with a vengeance if it isn't correctly discarded.


Allanah Dykes is a freelance writer and her work has been featured on Elite Daily, Levo League, Popsugar, Complex, Gurl, The Kitchn, HelloGiggles, Revelist, and Food 52.

View Work