Description: Unwanted moisture in concrete floors annually causes millions of dollars in damage to buildings in the United States. Problems from excessive moisture include deterioration and de-bonding of floor coverings, trip-and-fall hazards, microbial growth leading to reduced indoor air quality, staining, and deterioration of building finishes. Understanding moisture in concrete leads to design of floors and flooring systems that provide excellent service for many years. This publication discusses sources of moisture, drying of concrete, methods of measuring moisture, construction practices, specifications, and responsibilities for successful floor projects. The second edition incorporates a brief discussion of terrazzo issues, an extended discussion of issues with ASTM F1869 moisture emission testing, additional references on drying times of lightweight concrete, and updates to the sources of supplies and standards.
Two fundamental concepts permeate this writing: 1) the floor is part of a building envelope, but 2) also is in itself a system comprising many elements. For a floor to function successfully, specifiers, builders, owners, and finish/flooring installers each must understand the factors for floor performance, especially moisture. In the past few years since the first edition, we have witnessed significantly increased dialogue between general contractors, construction managers, concrete contractors, flooring installers, and design professionals. The industry has introduced new and improved products including flooring adhesives, vapor retarders, and moisture suppression coatings. New moisture test instruments are on the market due to the widespread adoption of relative humidity testing. The industry has essentially eliminated the use of a blotter/cushion layer above vapor retarders in new slabs-on-grade construction, resulting in fewer chronic problems. However, moisture problems persist due to schedule demands, limited awareness of moisture issues, and sensitivity of some finishes and flooring systems.