Concrete Subfloor

A subfloor is a layer of material installed directly over the structural floor joists in a building. It serves as the foundation and support for the final flooring material, such as hardwood, carpet, tile, or vinyl.

The subfloor provides a flat, level surface and helps distribute the weight of foot traffic and furniture evenly across the floor, ensuring stability and preventing the final flooring from flexing or sagging. It also acts as a barrier, protecting the underlying structure from moisture and providing a base for additional flooring layers or underlayment.

Plywood is among the most common materials used for subfloors, particularly in North America. Read on to learn more about plywood subfloors, their relative strengths and weaknesses, and things you should keep in mind when installing floors over them.

Benefits of Concrete Subfloors

Concrete offer a number of great benefits, such as:

  • Durability and Longevity: Concrete subfloors are highly durable and can withstand heavy loads, making them suitable for high-traffic areas in both residential and commercial buildings. Properly maintained concrete subfloors can last for decades without significant wear or damage.
  • Moisture Resistance: Concrete is naturally resistant to moisture, making it an ideal choice for areas prone to spills or water exposure, such as basements, kitchens, and bathrooms. With the right sealants and coatings, concrete subfloors can provide excellent moisture protection.
  • Stability and Levelness: Concrete subfloors offer a stable and level surface for various types of flooring materials. They prevent floor coverings from flexing or warping, ensuring a long-lasting and secure installation.
  • Energy Efficiency: Concrete has excellent thermal mass properties, helping to regulate indoor temperatures by absorbing and slowly releasing heat. This can contribute to energy efficiency and reduced heating and cooling costs.
  • Fire Resistance: Concrete is non-combustible and has high fire-resistant properties, adding an extra layer of safety to the building.
  • Low Maintenance: Concrete subfloors require minimal maintenance compared to other materials. Regular cleaning and occasional sealing can keep them in good condition for many years.
  • Versatility: Concrete subfloors can be used with various flooring types, including tiles, hardwood, carpet, vinyl, and more, offering design flexibility.
concrete slabs

Downsides Concrete Subfloors

Despite plywood subfloors having many advantages, there are also some downsides that you should consider:

  • Installation Complexity: Pouring and leveling concrete requires specialized knowledge and equipment, making the installation process more complex and time-consuming compared to other subfloor materials.
  • Initial Cost: The initial installation cost of concrete subfloors can be higher than some alternative materials due to the labor, materials, and equipment involved in the process.
  • Cracking: While concrete is durable, it can develop cracks over time due to settling, temperature fluctuations, or structural movement. Proper preparation and reinforcement can help minimize this issue.
  • Lack of Insulation: Uninsulated concrete subfloors can feel cold, especially in colder climates, which may necessitate additional floor heating systems or the use of insulating underlayment.
  • Limited DIY Feasibility: Concrete subfloor installation is typically not a DIY-friendly project due to its complexity and specialized requirements.

Flooring Installation Methods That Can Be Used On Concrete Subfloors

Several installation methods are used to install floors over concrete subfloors, and the specific method chosen depends on the type of flooring material being used.

These are are some of the most common installation methods that work with installing on concrete subfloors:

Floating Installation:

  • Flooring Types: Laminate, engineered wood, luxury vinyl plank (LVP), and luxury vinyl tile (LVT).
  • Method: The individual planks or tiles are interlocked or glued together, but they are not attached to the concrete subfloor. Instead, they “float” above the subfloor, allowing for some expansion and contraction. A foam or cork underlayment is typically used to provide cushioning and support.

Glue-Down Installation:

  • Flooring Types: Hardwood, engineered wood, vinyl sheet, and some cork flooring.
  • Method: Adhesive is applied directly to the concrete subfloor, and the flooring is firmly glued in place. This method creates a strong bond between the flooring and the subfloor, offering stability and preventing movement.

Nail-Down Installation:

  • Flooring Types: Solid hardwood and certain types of engineered wood.
  • Method: For solid hardwood, the flooring is attached to the subfloor by nailing or stapling it through the tongue into the concrete. Engineered wood may also be nailed down, depending on the thickness of the top layer and the manufacturer’s recommendations.

Tile Mortar Bed Installation:

  • Flooring Types: Ceramic or porcelain tile, natural stone tile.
  • Method: A thick layer of mortar or thin-set is troweled onto the concrete subfloor, and the tiles are pressed into the mortar. The mortar bed creates a stable and level surface for the tile installation.

Installing Flooring Over Concrete Subfloors: Additional Things To Keep In Mind

If you’re thinking about installing floors yourself over concrete subfloors, there are many things that you should be cognizant of. Here are just a few things to name to keep in mind:

  • Moisture Concerns: Concrete can retain moisture, which may lead to problems with certain flooring materials like hardwood or laminate. Proper moisture testing and the use of vapor barriers or sealants are essential to prevent moisture-related issues.
  • Uneven Surfaces: Concrete subfloors can have imperfections such as cracks, rough spots, or uneven areas. Leveling the subfloor with a suitable patching compound or self-leveling underlayment is necessary to create a smooth and even surface for the flooring.
  • Type of Flooring Material: Different flooring types have specific installation requirements. Consider the compatibility of the flooring material with the concrete subfloor and choose the appropriate underlayment to provide the necessary support and cushioning.
  • Underlayment Selection: Selecting the right underlayment is crucial for proper flooring performance. Each flooring type may require a specific underlayment material, such as foam or cork for laminate, cement backer board for tile, or a moisture barrier for hardwood.
  • Adhesive Compatibility: If adhesive is necessary for the flooring installation, ensure it is compatible with both the flooring material and the concrete subfloor. Using the wrong adhesive can lead to poor bonding and result in flooring failure.
  • Transition Areas: Plan for smooth transitions between different flooring materials and rooms. Proper transition strips or thresholds should be used to create a seamless and visually appealing flow between spaces.
  • Acclimation Time: Allow the flooring material to acclimate to the room’s temperature and humidity for the recommended time before installation. This helps prevent expansion, contraction, and warping after installation.

Ultimately, concrete subfloors offer many benefits and concrete makes for a great subfloor variety to install floors on. However, there are many nuances that you should know, and a degree of difficulty it takes to install floors over concrete. Therefore, if you have concrete subfloors, it is best advised to let a professional handle the installation.

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