Concrete moisture damages floor often in the Las Vegas – Henderson area as the desert climate enhances upward movement of vapor.

 

Understanding flooring failures due to excessive concrete vapor emissions is to first realize the water within the concrete is the culprit. Although moisture can condense on the surface of the slab prior to being covered with a floor or floor coating, the most common source of moisture is from the concrete itself or water from surrounding soils moving into the concrete even water flowing toward the slab should the local landscaping be higher than the slab.

 

Once moisture is in the concrete the law of physics comes into play as water and water as a gas (vapor) moves upward when the right conditions are offered in the building itself.  Much of this has to do with the location of the building and the environment the building is placed. For example, Arizona, Southern California and Las Vegas are locations of low relative humidity and higher temperatures and vapor moves upward, and inward, when the concrete slab is at 100% Relative Humidity (Rh) and the building’s interior environment is at 20% Relative Humidity (Rh). Moisture Vapor moves from high concentrations to low concentrations and the result is adhesive or coating failure as the vapor turns to water once above the slab surface and under the flooring material.  Vapor  pressure and the movement of vapor from low to high cannot be stopped. Remember that vapor is what turns turbines and steam engine locomotives.

 

The financial losses to contractors, manufacturers and flooring retailers is staggering and we often hear numbers of millions per year and over a billion dollars in loses over the past decade.  These financial losses are real yet unexplainable to anyone with common sense possessing a basic understanding of water and water as a gas.  This may seem a bit harsh, but the facts are in and the simple facts are:

  • Water runs downhill.
  • Vapor in the air condenses on cool surfaces (glass of ice tea or cold concrete slab)
  • Vapor as a gas always wants to be equal in density, meaning equal in Relative Humidity. Vapor moves from high concentrations to low concentrations to become equal.
  • Vapor moves from cooler temperature to higher temperatures and solidifies to water from higher temperatures to cooler temperatures.
  • Vapor, as a gas, moves upward. Gas is lighter than air.
  • Rain starts out as vapor in a cloud that cools, solidifies to a liquid and falls to earth.
  • Water evaporates into the air as a gas, to again fall to earth as a liquid.
  • Bottom line: Vapor goes up, water goes down.
  • Cooling air within the building lowers the RH, and solidifies the vapor to water, called Dew Point. This falls to the concrete surface.

 

Dew point failures are most often found in adhesive failures as the vapor condenses on the adhesive as buildings are cooled. In other words, the air conditioning is turned on in the morning to bring the building to a more comfortable working condition or warm air entering buildings through open doors into a conditioned atmosphere. Dew point is defined as :The dewpoint temperature is the temperature at which the air can no longer hold all of its water vapor. The vapor solidifies into a liquid and falls to the concrete surface or into the adhesive. This is Rare.

 

Then there are the basics of concrete which is; Water is a component of concrete, not some foreign unexplainable mystery unknown to the flooring contractors and builders.  Water, by volume, is 10% to 15% of the concrete mix and there can be no concrete without water. Because water is a component, water will always be welcomed back into the concrete whenever water is available to the concrete. No matter how dry the concrete becomes, it will always enjoy the return of water and absorb then release the water again when conditions are introduced. Moisture differences within concrete are never ending cycles of change that cannot be stopped, only controlled.

 

Understanding moisture and concrete are synonymous, as concrete cannot become concrete without the addition of water leaves the never ending question of:  What does a building owner, building contractor or flooring provider do to protect against moisture and vapor related failures?

 

Preventing Concrete Vapor Emissions Failures is Achievable

 

Prevention begins with some basic facts about concrete.

 

  1. As Concrete ages the inner capillarity’s becomes larger.  Capillaries are formed by the evaporation of water added upon batching the concrete mix.  As vapor moves through the capillaries they are cleaned. Free Alkali moves upward with the movement of the water vapor causing older concrete to emit vapor at higher volume compared to concrete after initial cure.
  2. Newly poured concrete contains 10% to 15% water, by volume. Water will forever be a component of concrete and concrete NEVER dries.
  3. Concrete absorbs water after full cure is achieved, whenever water is available. (link to water sitting on the side of a slab)
  4. If water is present within the slab, the color of the slab is blue to dark blue depending on the amount of water remaining within the slab.
  5. Power Troweling slabs agitates the aggregate and cement fines to the surface building a hard matrix wear-layer that is dense enough to trap hydration water to later cause flooring failures. (link to power troweling)
  6. Vapor barriers placed under slabs are often clear plastic or plastic not meeting vapor barrier standards. (link to vapor barriers).
  7. Vapor barriers placed under newly poured slabs are often cut by the placement contractors to allow excess mix water.
  8. The higher the water to cement ratio, the more vapor is allowed to move through the slab. Water to cement ratio is the main cause of excessive vapor movement damaging installed flooring materials and coatings.  (link to water to cement Ratio)
  9. Just because the existing floor did not fail due to excessive vapor emissions does not equate to a slab low enough in vapor emissions to install a new floor.
  10. Plastic vapor barriers degrade with age and are temporary, not permanent. Quality of the barrier and available alkali from concrete and acids from soils determine length of service.
  11. It is the responsibility of the Building Engineer, Architect and Specifier to design buildings and surrounding elevations to force water to flow away from the side of the slab.
  12. It is the responsibility of the Flooring Installation Contractor to inspect the building and surrounding grounds for problems with water flowing toward the building and check downspouts, ect.
  13. Moisture vapor moves upward only within the slab.
  14. Water flowing to the slab will be under the slab, on top of the plastic then upward