Do you need a waterproof membraine if installing floor boards directly onto concrete?

If you understand that concrete is a porous material that absorbs and has moisture in it, you then should also understand that this moisture will move toward the top surface of a concrete floor. This moisture will promote mold growth and will also destroy the bond of of most adhesives.

Membrane coatings are prone to failure when this moisture carries alkali in concrete to the surface. You are much better off using a penetrating sealer such as "StableCrete" to waterproof the concrete. This product penetrates to form a solid in the capillary/gel-pore system of a concrete. This stops moisture migration and provides for a superior bond to the concrete.