Concrete Flooring Moisture Failure Causality and Testing - a Multi-Industry Inability to Let Go of Incorrect Terms and Methods - Part 2

As in the first part of this article series, there can be a real attachment to just about anything that sounds "scientific" to explain problems associated with flooring failures; with this next fallacy being yet another example: Flooring Failures caused by moisture vapor pressure.

Vapor Pressure in a Livable Environment

This subject is being restricted for the exact issue of environmental vapor pressure causing flooring failures rather than an overall examination of vapor pressure(s).

In a livable environment, the vapor pressure than can build up underneath a floor is impressive, well impressive that a force that generates LESS than 1.0 psi has been so widely disseminated and accepted as a cause of flooring failures, even failures associated with epoxies, which generally have greater bond strengths than the cohesive properties of the concrete itself (well over 100 psi).

What Causes Vapor Pressure?

Vapor pressure is created when there is a difference in temperatures and/or humidity from one area to the next. This is a natural tendency towards equilibrium, which in the field, irrespective of what you might have read, or heard, or is claimed, NEVER happens in the vast majority of field conditions. The moment a temperature change occurs, or there is a change in humidity, this is when there is a reciprocal change in vapor pressure and the equilibrium attempt is once again in motion.

Generally speaking, and in an unobstructed environment, vapor pressure increases with increased temperature as well as increased humidity. The reverse is also true.

Now if someone actually thinks about the duality of temperature and humidity BOTH influencing vapor pressure, what happens if something blocks either of these conditions? The result is that the influence governing vapor pressure is greatly reduced, which is exactly what happens when a floor covering is installed! A floor covering is an effective way to reduce vapor pressure since humidity differences are for all intents and purposes, severely retarded if not eliminated. This leaves ONLY temperature differences as the determination of vapor pressure.

Moisture Vapor Pressure Realities

When a coating. covering or flooring is installed, the typical differences between the interior environment and the concrete temperature will create a net vapor pressure based solely on the respective temperature DIFFERENCES. In a livable environment, where most of the floors, coatings and coverings are installed, this will create a net vapor pressure typically less than 0.25 psi.

To place this in perspective, a pressure of 0.25 psi usually cannot even be felt, much less create pressures sufficient to disbond a coating or floor covering. It takes approximately 2 psi to inflate a latex ballon, which is nearly ten times the vapor pressure in a typical flooring environment.

Worse, there have been MANY (and still are) presentations given to professional groups, even within the concrete industry where the declaration of moisture vapor emission causing disbondment of mortars, epoxy flooring, etc. is presented as a "known fact", with very few if any, challenging these assertions.

Ironically, it is one of the worst interpretations of "Moisture Vapor Pressure" which appears to have been extrapolated by what the 3.0 lbs and 5.0 lbs vapor emission limits used for calcium chloride tests meant.

The moisture in pounds is a calculated weight of the water, based on a 24 hour period over a thousand s.f. area. The misinterpretation was that these figures represented actual vapor pressure, not volume! This miscommunication, rather than being questioned, was simply accepted as it was then once again misinterpreted to mean the vapor pressures were a reality and capable of disbanding any type of flooring material.

and we wonder why there are so many moisture-related claims....look at the "expertise" being relied upon...

Bottom Line: Vapor Pressures DO NOT cause flooring failures!

P.S. There is chemistry within concrete that can disrupt what the calculated vapor pressures SHOULD be, creating chemical reactions that are independent from moisture vapor pressure.

Next: Moisture migration originating from the sub grade is the main cause of flooring failures.