Moisture Issues in Concrete Floors Part 1

This is a guideline of issues causes, remedies, concrete, installations, curing sealing, and toppings, decorative overlayments are also at risk because of their low permeability they also require “bond or primer” coats thus sealing the concretes surface.


Decorative Concrete toppings and repair products can be used effectively and give new looks and provide long lasting low maintenance flooring systems.  Always follow the technical installation methods for each system installed and provide proper concrete surface profiles.  Although one if not the most effective systems used care needs to be taken in installing decorative systems. How we respond to the moisture issues today will allow for continued successful use of these materials.

From warehouses, restaurants, schools, hospitals, and almost 100% of industrial and commercial buildings all pick concrete.  Most provide useful floors and structures without problems while providing a long service life for owners.Construction of modern buildings would not be possible today without concrete floors.

If a concrete floor is allowed to remain relatively dry while in use many problems can be avoided.  Concrete needs water in order to begin the hydration process; however unwanted moisture in concrete floors causes millions of dollars of damage and lost time each year to owners of concrete floors.


Moisture problems have increased for a number of reasons:

¨Curing and sealing of concrete; September of 1999 new VOC laws changed both formats and application methods and more than ten years later most do not understand the methods.

¨Fast track construction also really began over the past 20 years.  “Time is of the essence” is written in contract documents which put everyone under a certain time frame and general contractors in a bad mood.

¨Lightweight aggregates and aggregates that absorb moisture are being used.

¨Tighter time frames of building construction.

¨EPA restrictions on land results in some buildings being built on marginal land.

¨Changes in concrete mix designs including the use of both slag and fly-ash results in slower cure times.  Set retardants and admixtures also have contributed to these issues.

¨Failure of tradesmen to stay abreast of new emerging trends.

The previous has also contributed to moisture vapor transmission problems.

Moisture Vapor Transmission (MVT):

MVT is a natural migration of gaseous water from a high moisture source to an environment with a much lower concentration of moisture.  An example of MVT is the relationship between the subgrade soil and grading materials and the concrete slab directly above it.

Many times water migrates into the concrete from the material beneath it in a gaseous or liquid state.  The moisture then migrates to the top surface of the concrete.  The migration takes place in the natural capillary pours within the concrete slab.

If the concrete slab is sealed with an impervious flooring system, the moisture vapor cannot pass through the floor.  As the internal pressure increases, the flooring system or the adhesive many lose bond which results in flooring failures.

Just a simple understanding of the general physics MVT can go a long way in understanding the issues involved.  When the humidity in the concrete is higher than the humidity in the air above, the water vapor begins to migrate to the concrete surface as a gas.  If a flooring system has an impervious coating that prevents the moisture to pass failures can occur.

Note:  2-3 lb of pressure is not enough to cause failures in a well bonded floor.  Larger amounts of pressure, however, can cause serious damage to floor coatings.  This can present failures from minor trip hazards to costly repairs (which may also fail,) or worse yet, lawsuits. There are products now available that, when properly applied, will allow coatings to be applied when the MVT pressure is 12-15 lb.  Each job should be evaluated when these conditions exist before application of coatings.

Pre-job conferences are important to discuss such issues (when moisture becomes an issues no job is too small).  ASCC offers an excellent check list for meetings.

The following outline will address these issues:

  • Damage caused by excess moisture.
  • Discoloration of both floors and coatings giving an unacceptable appearance.
  • Delaminating of floor coverings and coatings.
  • Growth of microbes that can lead to poor indoor air, odors, and even some allergic reactions.
  • Deterioration of wall coatings and mold reactions inside the walls.
  • Corrosion of items embedded in the concrete or attached to the concrete.
  • Damage to items stored on the concrete.
  • Safety issues such as slipping.
  • Issues that lead to MVT problems.
  • Subgrade soil.
  • Soils that did drain before construction that become compacted and do not drain.
  • Subbase.
  • Capillary breaks.
  • Vapor retarders.
  • Cleaning compounds.
  • Cures and sealers.
  • Primers and adhesives.
  • Excessive cleaning with water.
  • Putting the concrete into service too soon.

See Part 2: Moisture Issues in Concrete