How to Prepare a Wood Subfloor for a Hardwood Floor Installation

Wood subfloors are the preferred type of subfloor for solid hardwood flooring installations. They are easier to work with, but still provide a solid foundation to support your hardwood floors for years to come.

Your subfloors play an integral part in the success of your hardwood flooring. Even though the subfloor cannot be seen, you must go through the adequate process to ensure it’s ready to support your hardwood before you lay any planks. Here’s how to prepare your wood subfloor so you ensure a successful installation.

Step 1: Test the Integrity of the Structure

Because the subfloor is your hardwood flooring’s foundation, the structure must be strong and sturdy. For wood subfloors, there are a few ways to test for the structural integrity:

  • Walk on the floors. If they feel squeaky or hollow in certain areas, you might have a weak point.
  • Countersink a nail or screw into the floor. If it can’t be done, or the screw cannot be leveled, you should replace the subfloor.
  • Check the thickness. Most manufacturers require that your wood subfloor, plywood or OSB, is at least ¾ inches thick.

If you’re unsure about the integrity of your subfloor after going through these tests, call a contractor. Don’t jeopardize your installation because your subfloor is not up to par.

Step 2: Ensure the Floors are Flat and Even

If the structure is intact, you’ll also need to ensure that you’re working with a flat and even surface. Many people mistake this with a “level” surface. That’s nearly impossible to test because there is usually not a level to span across the entire room. Instead, you should look for any dips or holes in your flooring that are bigger than 3/16 of an inch.

To test your floor, get an even 8 to 10 foot plank. Then, lay it across your flooring to find uneven spots. Mark any areas where you see dips in the foundation.

If there is a small hump, you can probably sand it down without damaging the structure.

If you find large dips and vast low spots, fill them with a floor patch or leveling compound. To do this, add the water to the dry mix and stir. It should be a relatively thin mixture. Then, estimate how much you’ll need to fill the dip. Once you have enough, use the board to level the top of the filled area. Even if it does not look perfect, but it is level, the repair will work.

Planning on nailing or stapling your hardwood floors to the subfloor? Do not overuse the floor patch. You could crack your subfloor, causing more damage.

Step 3: Test for Moisture Levels

Moisture is dangerous for hardwood flooring. It will swell and slowly erode your floors, putting them at risk of buckling, warping and needing to be replaced.

Before you begin your installation, use a moisture kit. You should not have more than 4% moisture in the room or near the floor.

For further protection, you should also consider using a vapor barrier film for solid hardoowds or an underlayment with a moisture barrier for engineered hardwoods. To use this, you’ll cover your subfloor with the underlayment, taping down the rows. This helps keep out excess moisture that could seep up from the concrete below.

Once you’ve ensured that your wood subfloor is up to par, it’s time to put the finishing touches on your preparation. Sweep the floor and clean it of dust or dirt. The better you prepare your subfloor, the more successful your installation will be.

Have questions? Need a little bit of extra help? We’re here for you. Start a chat with one of our flooring experts in the box on this page and get a fast answer to your flooring installation questions.

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