Installing a hardwood floor over a concrete slab?         Back

Even if your home was built on a concrete slab, you can still enjoy the beauty and charm of hardwood floors. Here are nine things you should consider before the job is started.

• At or Above Grade - With the right subfloors, solid hardwood floors can be installed on slabs that are either on-grade (at ground level) or above-grade (above ground level). Moisture can pose problems for solid hardwood floors below ground level, so engineered wood floors (made of layers of wood glued together) are the best choice there.
  
  
• Protect the Flooring - Wood floors should not be subjected to very wet conditions. Before delivery to the site, the building should be closed-in with outside windows and doors in place. All concrete, masonry and sheet-rock should be completely dry. In warm weather, the building should be well-ventilated. In winter, heating should be maintained near occupancy levels at least five days before the flooring is delivered and until sanding and finishing are complete.
  
  
• Dry Slab - Concrete slabs, whether new or existing, must be dry before the subfloor is installed. For best results, several areas of each room should be tested for excess moisture. If tests indicate too much moisture is in the slab, do not install hardwood floors. A new moist slab should be allowed to dry naturally or the process can be hastened with heat and ventilation. Slabs less than 60 days old are generally too wet to install floors.
  
  
• Test for Dryness - To check a light-colored concrete slab for moisture, place a flat, non-corrugated rubber mat on the slab. Weight it to seal it against the surface. Look under the mat after 24 hours. If the covered area shows dark, wet marks, there's too much moisture evaporation from the slab. For other concrete floors, tape a 15-inch square of clear polyethylene film to the slab with moisture-resistant tape, sealing all four edges. If no condensation collects under the film after 24 to 48 hours, the slab is dry enough for floor installation.
  Flat, Clean Slab - The slab must be flat with a trowel finish, free of grease, oil, stains and dust. Grind off any high spots and fill any low spots.
  
  
• Vapor Barrier - With solid hardwood floors, a proper vapor barrier must be installed on top of the slab to make sure normal slab moisture does not reach the finished floor. Layers of asphalt felt with asphalt mastic or 6 mil polyethylene sheathing are the best choices.
  
  
• Subfloors - Two nailing surfaces are recommended: either three-quarter inch thick plywood or two-by-four-inch (2X4) sleepers. Either system will work for three-quarter inch flooring up to four inches wide.
  
  
• Plank Flooring - Plank flooring four inches and wider requires either the plywood-on-slab system or the sleeper system topped with three-quarter inch thick plywood.
  
  
• Acclimation - When the site is prepared, the flooring can be delivered and stored in each room where it will be installed. It will take at least a week to let the flooring become acclimated. The flooring should be removed from its boxes and all packing materials during this process.