It is not recommended to install solid wood flooring over a concrete slab. Although this is the general rule, there have been successful installations of solid wood flooring installed over dry, concrete slabs. This entails several additional steps. A plastic barrier is set over the slab and taped at all seams. Then some sort of moisture-resistant wood subfloor (marine plywood) is built on top of the plastic film. Then the flooring is nailed to the wood subfloor. If you decide to take the chance be sure to consult with the manufacturer as to their recommendations. Be aware, you may be voiding your warranty.
There is a new synthetic underlayment product on the market (called Sika AcouBond) that may allow for installing solid wood flooring over a dry slab. Check with the manufacturer of the wood floor to see if they will warranty this type of installation and what their recommended installation procedures are for this type of installation.
What wood floor can I install over a concrete slab?
With the improvements in hardwood floors most engineered and longstrip engineered plank floors can be used over a concrete slab. Manufacturers do not recommend using solid wood floors over a slab. Engineered planks and strip wood floors can be glued directly to a clean, dry, well-cured concrete slab. Some engineered wood floors can be glued at the tongue and grooves and then allowed to be floated over a special padding that is laid over the concrete slab. Longstrip engineered planks can be floated over the slab with a padding underneath. There are some new "hybrid" engineered floors that can be floated over a concrete slab and come with a click (glueless) tongue and groove locking system.
Note: New concrete slabs need to be fully cured for a least 60 days. All wood planks should be acclimated for 24-48 hours prior to installation. Be sure to read and follow the manufacturer's recommended installation procedures.