Hardwood Floor Over Concrete

I really would like to have a solid hardwood floor but my existing house has a concrete slab. Is it possible to install a hardwood floor on top of concrete? How in the world do you attach the strips of hardwood to the concrete? What needs to be done to insure that the floor looks as good as one installed on a wood sub-floor?

If your slab surface is level with the outside earth or is an elevated concrete slab you can install traditional hardwood flooring over it. Concrete slabs that are below ground level are not candidates for solid hardwood flooring. If you have such a slab, I would consider installing an engineered hardwood flooring. This material is made by taking different plys or layers of wood and gluing them together to make a wood product that is more stable when subjected to elevated levels of humidity often found in basements or below grade slabs.
Wood is a hygroscopic material. In other words wood changes its shape in response to changes in relative humidity or the presence of liquid water. As the humidity goes up or if wood gets wet, it swells. As the wood dries it shrinks or contracts. This type of movement can cause all sorts of problems with finished wood floors or even wood furniture. For this reason it is important that the hardwood stays dry and at or near constant humidity levels before, during and after installation.
To successfully install your hardwood floor over the concrete you need to make sure the concrete is dry. If the slab is new, it usually takes a minimum of 60 days for it to release sufficient moisture before you can proceed with the hardwood installation. If you are building a new home be sure the contractor installs a high performance cross laminated vapor barrier under the concrete. These vapor barriers are often used in high end commercial jobs and are very nearly impervious to any vapor transmission. They are also very puncture resistant.
To test any slab for excess moisture simply vacuum a small area first. Then tape a 15 inch square piece of clear polyethylene film to the slab using two strips of duct tape along each of the four edges. If no condensation or fog develops under the plastic after 48 hours, the slab is sufficiently dry. If the slab is wet, then heat the space and open windows or use a dehumidifier to draw moisture from the slab. Retest the floor for moisture content once you think it has dried.
The hardwood flooring is fastened to plywood or 2 x 4 strips that are securely attached to the concrete. Keep in mind that the height of your finished floor will end up at least one and one half to two and one quarter inches above the slab height depending upon which wood subfloor you decide to use. This raised floor can be a problem at doorways if you or the builder do not plan for this.