How To Clean A Plywood Subfloor? (6-Step Guide)

When tearing up old flooring, you may encounter a subfloor that needs a little TLC. You are probably asking, why do I need to clean my subfloor if I’m just going to lay new flooring over it again? Old flooring can leave behind adhesives that can make leveling your new floor a nightmare. Moreover, carpet is notorious for leaving mold, mildew, pet odors, and other unpleasant smells that no one wants in their home.

Just as your house or business is built on a foundation, the subfloor acts as a foundation for your new flooring. Any imperfections in the foundation can lead to problems and headaches down the road. Let’s take a look at how to properly clean a plywood subfloor so that you can make your next flooring project a breeze.

What You Need To Know About Cleaning A Plywood Subfloor ?

Exactly how you clean your plywood subfloor will depend on what type of flooring used to be present and what gets left behind in the removal process. You will need to physically strip old adhesives and fasteners, while things like mold and pet urine can be eliminated using cleaning agents. 

Regardless of the type of old flooring you had, make sure not to go overboard with getting the subfloor wet. Moisture is the reason that mold and mildew can form, and it is also responsible for rotting and warping wood. Expect to use some water to clean any residue from the subfloor, but be sure that the floor can dry quickly to avoid inflicting any more damage.

Supplies You’ll Need For Cleaning A Plywood Subfloor

  • Paint scraper/putty knife
  • Nail pullers/hammer
  • Screw gun
  • Broom/brush/mop
  • Bucket
  • Shop vac
  • Heat gun/hair dryer
  • Orbital palm sander/floor sander
  • Vinegar/bleach/Borax/hydrogen peroxide
  • Fan
  • Mask/respirator
  • Safety goggles
  • Gloves

How To Clean A Plywood Subfloor ? (6 Steps)

Step 1: Analyze The Subfloor

The first step is identifying your problem areas so that you can properly fix them. This will let you know what cleaning materials you will need and which ones won’t be necessary. 

Hardened or sticky resins left behind by things like carpet can usually be heated, scraped, or sanded away. Mold and mildew are better tackled with cleaning products, trying to sand these away will only lead to you breathing them in. If you find signs of mold, you will want to purchase a mask or respirator to protect your lungs.

Now would be the time to replace any sheets of overly damaged plywood. You can’t really fix warping or rotting, so you should start with fresh pieces for your subfloor to ensure a long-lasting product.

Step 2: Prep The Room

This is especially important if your subfloors are showing signs of moisture. Open any windows and get a fan circulating air to help dry the room out. Moisture can be a subfloor’s worst enemy, so we want to remove as much of it as possible. If you use a strong fan, be sure not to aim it directly at moldy spots because this will only make it easier to breathe in.

Vacuum any areas that may have loose dirt and dust laying around. It’s not uncommon for bits of the previous flooring to be left behind, so be sure to use a shop vac to get rid of as much as possible.

Step 3: Remove Adhesives & Fasteners

If any nails or screws have worked themselves loose since the subfloor was installed, you should replace them or at least make sure that they aren’t in the way. This means either pulling nails and replacing them or hammering them in further so that they don’t create any lumps in the flooring.

Adhesives like wood or carpet glue should be scraped or sanded off. If the adhesive is proving tough to remove, using a heat gun or hair dryer can help soften its bond. Just be sure to wear gloves so that you don’t burn yourself on the hot glue. Once it is heated, it should be much easier to scrape away with a flat edge, like on a paint scraper or drywall/putty knife. 

If you prefer to sand away these glues, use an orbital palm sander with 120-220 grit sandpaper for smaller sections or a floor sander for large areas. Just be careful not to disturb any mold if it’s present.

Step 4: Clean Mold & Mildew

Mold and mildew can be tough to combat in humid climates, but it’s imperative that they get removed before laying a new floor. While they don’t necessarily do any damage to your subfloor, they are signs of moisture, which will do considerable damage. 

This is where you need to be careful not to damage your subfloor. Wood will eventually warp when exposed to moisture for long periods of time, so we need to clean away the mold and mildew without ruining the subfloor.

In a bucket, mix a solution of either vinegar, hydrogen peroxide, OR bleach with water to kill these unwanted odors. A solution of one part vinegar or bleach to three parts water is a popular at-home recipe for killing mold. Diluting it also helps with the smell that can linger afterward. You can also use commercial cleaners like Borax to kill mold as well.

You can use a mop here, but it is a better idea to use a broom for larger areas and a brush for spot-treating mold. Mops tend to carry a lot of water, opening you up to the possibility of damaging your subfloor. Brooms and brushes won’t hold as much water, so they are the safer method. Apply and scrub away any signs of mold or mildew. You will want to give your solution a few minutes to work its magic, but we need to dry our subfloors as soon as possible.

Step 5: Dry The Subfloor

This is where fans and open windows come in handy the most. They will circulate the most air possible, drying the floor fast. You will want to aid this process by using a dry mop or towels to soak up any puddles or standing water that may have formed. Try to refrain from walking over your clean subfloor too much so that you don’t introduce any new substances that will need to be cleaned.

Step 6: Inspect

Check your work to make sure that no areas were missed. You may need to hit mold and mildew more than once to fully eradicate it. Your subfloor should now be free of any imperfections that will make it harder to lay new flooring.

Final Thoughts On Cleaning A Plywood Subfloor

Cleaning plywood subfloors is by no means a difficult task, but improper cleaning techniques can lead to doing more damage than help. The main takeaway here is to remove anything left behind from your previous flooring without using too much water. Removing fasteners and adhesives generally won’t lead to any damage, but cleaning out mold and mildew needs to be done carefully. Always take your time and check your work to ensure the best possible final product.

Meet your Flooring Expert

Travis McCullough

Travis McCullough

Travis is a lifelong jack-of-all-trades in the construction industry with 20 years of experience in a variety of fields. He’s tackled flooring, carpentry, and everything in between on residential and commercial projects of all shapes and sizes.
Working independently and as part of a crew has equipped him with the know-how to not only complete a project but also teach others the finer points within most building professions. When he isn’t out hanging off of a ladder or crawling around on a roof, Travis spends his time educating people about the construction industry.

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