Learning Objectives - After reading this article, you should be able to:
- Summarize the health hazards, flooring damage and other problems that can result from high levels of moisture in concrete floor slabs.
- Identify current methods for mitigating high moisture levels in concrete slabs.
- Describe a preemptive approach of using rapid drying concrete mix to solve moisture problems.
- Discuss the occupant health and project management advantages of using rapid drying concrete mix.
|1 AIA LU/HSW|
Moisture-related problems with flooring materials and coatings are today one of the most common and costly of construction issues. The direct and indirect costs associated with these problems are estimated to be in the hundreds of millions of dollars each year in the United States alone. The affects of high moisture levels in a concrete sub-floor can not only lead to failure of the flooring system but can also lead to costly construction delays, indoor air quality issues and the legal disputes that follow when these problems develop.
Moisture in the Slab
Water is an integral component of concrete and is necessary to properly hydrate the cement particles in the mixture. However, water beyond that which is necessary for hydration is added to concrete to create a mixture of a workable consistency. The additional water is known as; “free water” or “water of convenience.” Once the mix is poured and set, free water is released from the slab in the form of moisture vapor during the drying process.
Another source of moisture that can affect concrete slabs-on-ground is water in the earth beneath the slab. This moisture from the water table is constantly migrating upward through soils, in vapor form, until it reaches the underside of the slab. Ideally rising moisture is stopped at this point as it contacts a low-permeance vapor retarder in direct contact with the underside of the slab. However if adequate moisture protection is not in place below the slab, moisture in the concrete will increase over time.
High levels of moisture in concrete slabs can lead to flooring failures and health hazards.
Image provided by U.S. Concrete