Understanding moisture related problems, causes and the possible remedies

Moisture-related problems with epoxy flooring and coatings are one of the most common and costly of today’s 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 legal disputes 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 or the integrity of the vapor retarder is compromised moisture in the concrete will increase over time.


High levels of moisture in concrete slabs can lead to flooring failures and health hazards.

Floor Covering Failures
If flooring materials are installed on a slab before it has reached an acceptable level of dryness, moisture can either prevent epoxies from properly curing or lead to the breakdown of them due to the development of a saturated high pH environment at the surface of a slab. Epoxy degradation, blistering, disbondment and the expansion of flooring materials are all conditions that can be the result of excess moisture in the slab.

Owners and contractors are forced to wait an extended period of time for the concrete to dry naturally to an acceptable level, or incur the cost and disruption of installing a topical moisture mitigation system. In either case the costs can be significant and can delay the project completion beyond what may be acceptable.


Elevated moisture levels in a concrete floor slab can result in indoor air quality and costly flooring damage. Above are some of the visible signs of a moisture related problem.

Testing Moisture Emissions
Most U.S. manufacturers of floor coverings, adhesives, and resinous coatings require that moisture tests be performed prior to the installation of their materials and that the tested levels are at or below limits considered to be safe for the installation of their materials.

Historically the most common test required by manufacturers has been the measurement of the Moisture Vapor Emission Rate (MVER) by the calcium chloride method. Many manufacturers are now requiring that the concrete’s internal relative humidity level be tested also. These two test methods measure moisture in, or from a different portion of the slab. The MVER test measures moisture emitting from the top ½ in. to ¾ in. of the slab only. Measuring the concrete’s internal relative humidity helps to determine what the moisture level in the slab will be once the flooring materials are installed. It is important to understand that the results of either test can only be considered meaningful if a low-permeance vapor retarder is in-place directly below the slab and the testing is done under the same or similar environmental conditions under which the flooring products will be permanently exposed.

Testing the Concrete Surface pH Level
Most epoxy flooring manufacturers also require that a pH test of the concrete surface be performed. Soluble alkali salts are naturally present in concrete. However if there is sufficient moisture within the concrete to place these salts into solution, the pH level at the surface of the slab will rise to levels that can lead to the breakdown of adhesives and epoxy flooring materials. What is important to understand is that to perform a pH test one must introduce liquid water. If there is not sufficient water in the concrete to create a solution after the flooring system is installed, pH will not be an issue regardless of what the test indicated. In short, getting rid of the water and protecting the slab from moisture entering from below, will ensure that pH will not be an issue.

The First Line of Defense
The best preventative measure for moisture-related problems in flooring is time; time for the concrete sub floor to dry adequately. Time is required to allow moisture levels to reach the tolerances of the materials specified. With some exceptions for certain subgrade conditions (i.e. high groundwater levels), establishing realistic timelines and including testing for accurate moisture conditions prevents a significant number of moisture-related flooring problems.

However, as we so often hear, time is money, and owners and contractors increasingly find themselves spending money to mitigate problems time would resolve. Tight project schedules and the demand for maximized production mean that moisture mitigation systems have become more readily-used to manage moisture conditions in a slab, prior to flooring installations.

Moisture Mitigating Strategies
In the past, most projects have delayed implementation of a moisture mitigation strategy until it is certain that the treatment will be needed. Using this approach, the moisture level of the slabs is tested a few weeks before the flooring is scheduled to be installed. If the moisture levels are found to be acceptable, the moisture mitigation system is not installed. If, however, the moisture levels are not found to be acceptable, the system is installed. The biggest problem with this approach is that more often than not the floors are not found to be at an acceptable moisture level. Implementation of the mitigation system at this late stage significantly increases the cost and is a disruption to other trades.

The following approaches are currently being used to mitigate high levels of moisture in concrete sub-floors:

  • Accelerated Drying
  • Topical Treatments
  • Reactive Penetrants
  • Moisture Mitigation Coatings
  • Modified Cementitious Overlays
  • Alternative Finishes
  • Integral Admixtures

Once a moisture transmission problem is identified, it requires considerable time and testing to work through the sequence of treatments. Today’s technology, however, is beginning to solve the problems associated with moisture vapor transmission.  Please feel free to contact us to help navigate you through the complexities of the problem and the many treatment options.

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