Balancing the moisture and pH balance of concrete slabs

A familiar situation across plants nowadays is the following: Moisture content of precisely a new concrete slab met the flooring manufacturer’s recommendations. However, the concrete showed a high pH of 10 to 11. The result: The manufacturer wouldn’t warranty the finish flooring and construction ground to a halt.

By Bill Imhoff

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A Colorado facility recently faced a flooring dilemma that is becoming increasingly common around the country. The situation: Moisture content of precisely a new concrete slab met the flooring manufacturer’s recommendations. However, the concrete showed a high pH of 10 to 11. The result: The manufacturer wouldn’t warranty the finish flooring and construction ground to a halt.

A high-tech corporate and manufacturing facility in Austin, Texas struggled for 15 years with floor-tile failures due to moisture and high pH. It spent more than $250,000 to remove its failed floor tile and encapsulate the concrete slab with a moisture barrier to install a warrantable floor covering that will provide 2,000-psi strength for the massive machinery that moves across this floor (Figure 1).

Figure 1

Figure 1. Moisture and pH problems led to strip failure, stressed vinyl composition tile and efflorescence in the seams.

Behind the moisture-pH dilemma

Balancing the right pH and the right moisture level in slabs can be a challenging and often costly problem. Concrete has a naturally high pH. But, many flooring manufacturers won’t warranty installations if the pH is at those naturally high levels, even though moisture is low (Figure 2). Nationwide, moisture and pH-related flooring problems have reached the billion-dollar level annually, according to independent concrete flooring expert Scott M. Tarr, principal engineer at CTL Group, Skokie, Ill. Some factors driving these problems include:

Figure 2

Figure 2. Coatings failure and pH irregularity caused cracks in this floor.
  • Eliminating asbestos in resilient flooring
  • Banning solvents from adhesive and coating systems. In 1995, federal law banned the use of petroleum-based adhesives. New flooring glues are more sensitive to alkali environments, and eventually fail when pH is too high.
  • Raising concrete water content to allow easier placement
  • Absorptive aggregate in lightweight concrete
  • Fast-track construction schedules
  • Admixtures such as fly ash and reactive aggregates that can cause adverse reactions in the concrete
  • Constructing on fill material in less-than-prime areas.

"New innovative products, installation methods/materials and environmental regulations have produced a more complex environment in which floor covering products are installed,” notes the World Floor Covering Association (WFCA, in a recent study on flooring installation issues. Commercial and industrial facility managers have several options for dealing with that complexity to resolve moisture- and pH-related problems with floor coverings:

Conduct independent testing

The WFCA study recommends you use an independent specialist to test the suitability for installation as safeguard for general contractors, owners and architects. Consider only experts having in-depth understanding of the project, soil and underslab conditions, surrounding environment and the concrete itself. You should expect the testing to include checking the chemical composition of the concrete, the environmental requirements and the formulation technologies of the concrete and adhesives.

Test results are tough to analyze, particularly because the industry still relies on an analog test for calcium chloride. In use since the 1950s, calcium chloride testing has helped the industry develop data for acceptable moisture and pH levels. However, to ensure accurate readings, testing must be monitored to ensure an objective testing environment. Testing must be done in the finished floor’s operating environment to avoid introducing misleading information about the concrete’s reaction to that environment.

Humidity probes are newer alternatives and can provide more objective data. Even so, there is some debate on how to achieve a precise interpretation of the probes’ readings.

The pH of a surface is the measurement of the activity of hydronium ions. The pH level usually is tested by placing distilled water on the surface and using a device to measure the activity of the ion in the solution.

Because there’s been no testing of ion activity levels while the surface is dry, there’s no definitive evidence that pH would be a concern in the absence of moisture.

Some floors perform well in conditions that are as much as double the specified maximum moisture vapor readings for the selected floor finish, while others suffer chronically with readings at the maximum.

This is because determining the right moisture/pH balance isn’t an exact science.

You must balance the criteria for proper building technique and quality products with project economics.

In the end, you must base your decisions on how crucial the loss of an area would be to the business operation should the flooring fail and a warranty claim arise. In general, your flooring installer should follow manufacturer guidelines, unless the area is relatively small and can be repaired with minimal disruption if the floor finish fails.

Choose not to test

An alternative that avoids the issue and costly delays is to simply not test the moisture and pH levels. In that case, the installer bears the burden if the flooring should fail unless all of the parties involved (owner, contractor, architect) sign a waiver. The waiver acknowledges the parties’ responsibility if high moisture, pH or other inherent problem that exceeds the manufacturer’s recommendations causes a failure.

There are two primary scenarios in which a flooring installer might choose not to test:

  • Costs involved in honoring the floor warranty don’t outweigh the risks of not testing. The costs might include demolition, floor replacement, customer confidence damage, poor resource utilization for both the owner and installer and lost-use revenue.
  • The installer desires to be forced out of business because of the enormity of the loss with no possibility to recover, despite the negative aspects accompanying such a decision.

Ignore the standards and proceed

The flooring installer and manufacturer might elect to exceed standards and proceed with the installation anyway. A manufacturer may be willing to adjust the standard for the particular project and issue a warranty or modified warranty with stricter exclusions and exceptions. Otherwise, proceeding without a warranty means your installer must assume potential liability should the flooring fail, unless a waiver has been signed.

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