Which of the following is an essential item for installing 3/4" strip flooring over a concrete slab?

Installing 3/4" strip flooring over a concrete slab necessitates the use of vapor barriers. Concrete is a highly porous material that can absorb moisture from the ground. If this moisture rises to the surface, it can compromise the flooring above, leading to problems such as mold growth, warping, and deterioration of the flooring material.

A vapor barrier serves as a protective layer to prevent moisture from penetrating the flooring system. This barrier is typically made of heavy plastic or polyethylene sheeting that is laid over the concrete slab before the installation of the flooring. By keeping moisture at bay, the vapor barrier helps to ensure the longevity and stability of the strip flooring.

Other listed items, while potentially useful in different contexts, do not directly address the critical issue of moisture prevention in the specific scenario of installing strip flooring over concrete. For example, wood glue might be useful for certain adhesive applications, metal brackets are more suited for structural support, and timber joists are used in elevated flooring systems rather than directly on a concrete slab.