The Options for Installing Hardwood Floors Over Concrete

Hardwood Floor Types

• Hardwood floors are available in solid and engineered wood options. Solid wood floors are made from planks of solid wood you can install on grade or above grade. They are not recommended for below grade (basement) installation. Engineered wood floors are composed of three to nine layers of hardwood veneers. They do not expand and contract as much as solid wood floors with changes in temperature and humidity. These floors can be installed at or below grade, making them acceptable for basement installation when moisture is not an issue.

Moisture

• Before considering the installation of a hardwood floor, check the concrete slab for moisture. New concrete should cure for six to eight weeks for moisture to dissipate. In older concrete, test for the presence of moisture by placing a 15-inch square of polyethylene in several locations on the floor. Tape the squares down on all sides. After 24 to 48 hours, check the polyethylene for condensation. If no condensation is present, your concrete slab is suitable for the installation of a hardwood floor.

Leveling

• A level slab will give the most satisfactory surface for installation of your floor. The slab should be flat within 3/16 of an inch in a 10-foot radius. Check the surface by placing a straight edge on the floor in several locations around the room. If light is not evident from under the straight edge, your floor is level. Fill in low places with leveling compound and sand down high spots with a concrete grinder.

Plywood Subfloor

• Plywood is used as a subfloor for hardwood floor installation. Before installing a plywood subfloor, cover the slab with polyethylene to create a solid moisture barrier between the concrete and the plywood. Place 5/8-inch plywood over the vapor barrier and attach it to the slab using concrete fasteners. An alternative method is to create a floating floor. In this case, two layers of 3/8-inch plywood are fastened together over the vapor barrier. This method does not penetrate the vapor barrier, which ensures that moisture does not make its way to the wood above. After installing the plywood subfloor, the hardwood floor is either glued, nailed or stapled to it.

Glue-Down Method

• When installing a hardwood floor on grade, you can glue the wood directly to the slab, as moisture is not usually an issue. The floor must be clean and dry for the glue to adhere. A proper amount of a good adhesive designed for hardwood floor installation must be used. Engineered floors are more suitable for the glue-down method, since they are more flexible than solid wood.