FLOORING : Mix Wood, Concrete With Right Methods

Doomsayers will tell you that you can’t install wood flooring over a concrete floor or basement slab. Despite the popular notion that wood and concrete don’t mix, any kind of wood flooring--parquet, laminated, and even solid strip or plank--can be installed over concrete successfully by following the right techniques.

Preparation

Dryness of the concrete is the key. Before ordering wood flooring, test for moisture by taping several pieces of polyethylene film (available from building suppliers), each about 18 inches square, to the concrete floor in various locations. Seal the edges of each piece with duct tape. Check the pieces after 48 hours. If there is no moisture clinging to their undersides, the floor is sufficiently dry.

Laminated Flooring

Laminated flooring--thin layers of wood bonded together and shaped into tongue-and-groove panels--can be glued with mastic adhesive (available in flooring and hardware stores) directly to a dry concrete floor above ground level.

Start by cleaning the slab and covering uneven areas with cement-base self-leveling compound, a liquid that hardens to fill minor dips and hollows. After pouring the compound, smooth it with a long, straight board. When the compound hardens, spread mastic adhesive with a notched trowel and embed the flooring according to the manufacturer’s instructions.

Below Ground Level

If a concrete slab is below ground level, install plastic film as a vapor retarder after cleaning and leveling the floor. Its purpose is to reduce any moisture reaching the flooring.

Use a notched trowel to apply waterproof mastic adhesive. Start at a far corner and work toward the doorway. When the mastic dries, unroll sheets of polyethylene film over it, beginning at a doorway and working toward the corners of the area being covered. Overlap sheets by at least 4 inches and seal the seams with contractor’s sheathing tape. Press down firmly to embed the film; puncture any bubbles with a pin to release trapped air. Afterward, laminated flooring can be installed with mastic adhesive as described above.

Solid Wood Flooring

For a solid wood flooring--parquet and strips or planks--and to provide a flat, smooth base above a damaged floor, install widely spaced 2-by-4s called sleepers, which serve as joists, followed by plywood underlayment panels, which serve as new subfloor.

Cut sleepers 18 to 48 inches long from flat, straight 2-by-4s and place them on their wide sides at 12-inch intervals, perpendicular to the direction you plan to use for the finished flooring. Overlap the ends of the sleepers by at least 4 inches.

Above ground level, fasten the sleepers to the floor with masonry nails. Below ground level, apply a polyethylene vapor retarder with mastic adhesive and embed sleepers in it with the same adhesive. In areas where humidity is high, cover below-ground sleepers with an additional layer of polyethylene. Slabs of rigid foam can be placed between sleepers to provide insulation.

For underlayment, use a single layer of three-fourths-inch-thick plywood or two one-half-inch layers. Fasten the material to the sleepers with ring-shank nails spaced 6 to 10 inches apart; leave a gap of about one-eighth inch between sheets--one-half inch near walls--and stagger arrangement to minimize long seams. Strip and plank flooring up to four inches wide can be nailed directly to the sleepers without an underlayment.

Attach parquet flooring to underlayment with mastic adhesive. Use nails to fasten strips or planks.