How to Lay a Floating Subfloor over Concrete - Part One

A circular saw cutting plywood subflooring.
  • 24-48 hours
  • Beginner
  • $60-200
What You'll Need
Concrete sealant
Leveling compound

Installing a floating subfloor over your cement floor can add warmth, homeliness, and character to your room. You can create a floor that is appealing and that will act a barrier between the cold cement and your interior. Follow the steps below to begin preparations for this process.

The Underlayment

A floating subfloor is flooring that actually never touches cement underneath. It "floats" or rests on top of a waterproof underlayment instead. This may be made of various materials including polyethylene, plastic, or styrofoam. The underlayment exists to create an air-filled gap between the concrete below and the subflooring, which will help to insulate the floor and keep the room warmer. Additionally, the underlayment is always a waterproof material that will create a waterproof barrier.

The Subfloor

Subfloors are strong, versatile, and very durable. They are capable of sustaining heavy furniture or objects and stand up well to traffic. The aforementioned air gap created by the underlayment will give the floor a little bounce and create cushion. The underlayment also adds a softer feel to the floor than what you could get by just laying it directly over the cement. Most types come in two foot by two foot pieces that interlock with each other, which will make installation relatively simple.

Step 1 – Inspect the Cement Floor

The first thing you should do is prepare the cement floor for installation. Check the floor for cracks, excess moisture, or sudden dips. If you find any of these issues, investigate and research further before continuing with this process. For example, if you find cracks, you should check the foundation of your home because the problem may lie in the way the cement slab below your house was poured.

Treat the cement floor with a concrete sealant prior to installation if you find that your floor seems damp, wet, or that it collects moisture. If you have not previously treated your floor with sealant, you should go ahead and do this as a precautionary measure anyway, as the sealant will create a more waterproof barrier for the floor and will help protect the subflooring.

If you find that your floor has dips or is not level, you should properly level the floor by using leveling compound.

Step 2 – Prepare for Installation

Next, you will want to make sure that the cement floor is clean by vacuuming and sweeping to remove any dirt, soil, or debris. Then, it's time to let your subfloor material breathe. To do this, remove it from any packaging and allow it to stand in the room where you will install it for at least 24 hours prior. It is best to lay the flooring plastic side down, directly onto the cement floor. As a result, the material for the subfloor will acclimate to the temperature and moisture content of the room, expanding or contracting before the installation rather than after.

With that, you are prepared to commence with the installation of the flooring. The steps for this procedure will be covered in part two.