Concrete Coatings Articles

Moisture and Your Floor

Concrete is a very strong, durable material, and it is the primary substrate on which flooring materials are applied. What is well documented but seemingly not well understood are the problems that moisture can cause on a concrete floor that has been coated with non-breathing flooring materials.

Real-World Scenarios

Concrete is essentially a hard sponge. Like a sponge, it readily absorbs water from any available source unless it can be sealed on all sides. Most new slab-on-grade (or ground) construction incorporates a vapor barrier on the positive side of the concrete slab (aka the bottom side of the concrete). This vapor barrier is designed to prevent moisture from entering the slab from the ground.

If an effective vapor barrier is in place and the concrete is properly cured and dried, it can then be coated with an impermeable flooring system with a very high probability that there will not be a purely moisture-related failure. This is the near-perfect condition for applying impermeable flooring materials, but what of the many other scenarios? What happens when a vapor barrier isn’t used on the positive side? What happens when a vapor barrier is used, but there are still problems with the coatings delaminating?

No Vapor Barrier

In this scenario, the flooring contractor (we’ll call them ABC) has been told that a vapor barrier has not been installed under the concrete. ABC does not want to make a mess by performing a core sample to verify if there is or is not a barrier but does decide to perform ASTM F2170: Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes and ASTM F1869: Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride. The contractor follows the testing requirements to the “T” and creates a very nice report showing the owner that the average results using ASTM F2170 showed 75 percent relative humidity (RH) and ASTM F1869 showed an average of 3 pounds (1.4 kg) per 1,000 square foot (92.9 m²) per 24 hours. ABC goes on to state that the flooring manufacturer’s published literature shows that the flooring material can be applied to concrete meeting these test results. The owner is thrilled and ABC proceeds to install the flooring material.

After a wet autumn the owner notices blisters forming on the seven-month-old floor and contacts ABC. ABC finds blisters filled with an aqueous solution. He reruns ASTM F2170 and finds that the concrete is now showing RH values of 100 percent on every test. He explains to the customer that the only fix for the blisters is to totally remove the flooring material. He denies any wrongdoing, stating that he ran the proper tests and complied with the manufacturer’s technical data sheet. The customer is angry and threatens legal action against ABC and the material manufacturer. ABC loses the lawsuit and his reputation.

Thought There Was a Vapor Barrier!

A general contractor (GC) hired XYZ flooring company to install a 1/8-inch (0.3 cm) double broadcast epoxy flooring system to a converted auto repair facility. The GC tells XYZ that there is an existing vapor barrier. XYZ has done a number of jobs for this GC, so he takes the GC at his word and does not take a core sample, but XYZ does perform ASTM F2170. The tests show an average RH value of 78 percent, which is well within the range required by the material manufacturer.

The flooring system is installed and looks beautiful! Then, 13 months after the installation, the owner contacts the GC who contacts XYZ to say that there are slits with black goo coming out of them. XYZ determines that moisture is coming up through the slab and performs a core sample. XYZ finds that there is no vapor barrier in place, that the slab is contaminated with oil, and goes to battle with the GC. The battle results in a lawsuit and the end of what was previously a great relationship. All parties lose a great deal of time and money.

There Is a Vapor Barrier

COOL MAN, a vinyl composition tile (VCT) company, reviews the project specifications and finds that there was a required vapor barrier to be installed on the project he is about to start work on. COOL MAN meets with the project superintendent who tells COOL MAN that he was onsite when the concrete was poured and that the vapor barrier is definitely there. COOL MAN is glad to hear that and begins to prepare the concrete for the VCT.

Before long, the VCT installation is complete and COOL MAN’s work is done. The building is complete and occupied within four months from the date COOL MAN completed his work. But then, COOL MAN gets a call from the superintendent stating that the VCT is coming up all over the facility. COOL MAN visits the site and sees that what he has been told is true. He has many discussions with the superintendent and learns that the slab was poured long before the roof was on the building. He did not run any moisture testing because he wrongly believed that the existence of a vapor barrier meant that he did not have to worry about trapped moisture. COOL MAN owned up to his mistake but could not cover the losses and went out of business six months later. Water wicks up concrete just like a sponge. If this moisture is trapped above an effective vapor barrier it can cause moisture related failures once locked in.

Offer Protection

If you have been in the flooring business long enough you have heard of or even experienced situations like these. The fact is that there is great risk when applying impermeable floor coverings to slab-on-grade concrete construction. Performing and knowing how to interpret core samples is critical. Testing per ASTM F2170 and, to a lesser extent, ASTM F1869 is critical. But even when the flooring contractor has done these things, moisture-related failures are still a possibility. The best way to protect your company, your customers, and your relationships is to offer a moisture suppression system! These systems are designed to stop moisture migration from eroding the adhesive bond line of the flooring system.

It is critical that this offer be made in writing, stating that you cannot be responsible for moisture-related failures and that if they choose not to select the option of installing a moisture suppression system they do so understanding that they have no warranty for moisture-related flooring failures. When presented clearly and professionally there are few customers who will not see the wisdom in purchasing this much-needed protection.

About the Author:

Chris O’Brien, president and CEO of Rock-Tred Corporation, has worked with specification writers, architects, building consultants, general contractors, facility managers, and home and business owners over the past 23 years to design and execute coating and overlay projects that beautify and protect. He holds patents on both processes and equipment, has authored articles for numerous magazines, served on the board of directors for several profit and non-profit corporations, and is actively engaged in the manufacturing, marketing, and sales of specialty coatings all across the United States. For more information, contact: Rock-Tred, (888) 762-5873,

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