Can Wood Floors Be Installed Over Concrete?

You can install a hardwood floor over a concrete slab.

Hardwood flooring is unusual in its warmth and beauty. Low maintenance (so long as you protect it from spills and scratches), hardwood flooring is appropriate in any room of the house. Installing hardwood over concrete is certainly an option. The key is to do the prep work conscientiously; otherwise, the flooring will buckle or worse.

Moisture

Moisture is the main threat to hardwood wherever it is installed. Even spills of water need to be cleaned up immediately lest the floor stains. You can control moisture if the concrete slab on which you are installing the hardwood planks is on-grade or above-grade. If the slab is below-grade, you would do best to install an engineered hardwood floor. The concrete slab must be completely dry before you install hardwood (or any other) flooring. Do not guess; test the slab for dryness. And see that the wood flooring is dry too. Store it in a dry room at room temperature for at least five days before installing it.

Flatness

The concrete slab must be absolutely flat or the wood floor cannot be installed properly. Do not try to use a carpenter's level to test for flatness because it isn't long enough. To check for flatness, use a 6- to 10-foot long straightedge. Place it on the slab in various positions. If the slab is not flat, you will notice depressions and dips. Use a concrete-based self-leveling mortar to even out the floor, following the manufacturer's directions.

Vapor Retarder

You must install a vapor retarder on top of the slab to create a moisture barrier between the concrete slab and the hardwood flooring so moisture does not migrate from the concrete into the flooring. Some options are two layers of asphalt felt applied with an asphalt mastic or 6-ml polyethelene sheeting.

Subfloor

Next you would need to install a 3/4-inch treated plywood subfloor over the vapor retarder. Use concrete screws every 16 inches. Leave a gap of 3/4 inches along the walls and a gap of about 3/8 inch between the sheets of plywood for expansion. The best approach is to lay down the plywood at a 45-degree angle from the direction you will lay the floor to prevent cracks along the edges of the panels. Alternatively, you can screw rows of treated 1 x 4s to the concrete perpendicular to the direction you will install the hardwood flooring. The 3/4-inch plywood and the 3/4-inch thick hardwood flooring will raise the floor 1-1/2 inches, which could be a concern if you are installing the flooring around cabinets or other built-ins.

Hardwood Flooring

You must nail the hardwood flooring to the plywood subfloor or the 1 x 4s using a flooring nailer. If you are installing unfinished hardwood planks, the floor would then need to be sanded and finished.

References

• Hardwood Council.com: Installing a Hardwood Floor over a Concrete Slab
• Family Handyman Magazine; Installing Wood Flooring Over Concrete
• Wood Floor Doctor.com: Installing Hardwood Floors on Concrete Slab