There are many questions about gluing down solid wood flooring to concrete. The traditional industry standards for wood floor installation limited the direct glue down of solid wood flooring over concrete to short pieces or parquet patterns. A well made engineered wood floor looks like a solid floor but avoids some of the installation difficulties. The backer of the engineered flooring helps reduce the movement with moisture changes. For many applications this is the best solution.
With the advent of elastomeric adhesives gluing solid flooring directly to concrete has become more common. NOFMA produced a technical publication outlining recommended procedures for installing solid wood floors to concrete about five years ago. Despite the inherently higher risks of gluing solid to concrete it has become an accepted practice for many people in the industry. This installation method takes more effort to manage the risks. Moisture issues are the primary concern. Test to see if the concrete is dry enough. The ASTM F2170-2 test is a widely accepted procedure which measures the relative humidity inside the concrete. It is often prudent to apply a sealer to the concrete just in case moisture is introduced into the concrete at a later time. Then if the concrete gets wet in the future a trowel on moisture cured urethane vapor barrier or penetrating sealer such as Bone Dry which was applied prior to installing the floor can keep the water away from the wood. An alternative to a glue installation is to install a plywood subfloor over the concrete then nail down the flooring.