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Importance of Core Testing 

April 13, 2023

The other day, I had an interesting conversation with John Davis. John is a territory sales manager for Dur-A-Flex and has been in the floor coatings industry for over four decades.  

He was telling me how a water treatment plant in Texas was getting ready for a new Dur-A-Flex flooring system. Before moving forward with the selection, (as is standard practice), an in-situ Relative Humidity test was performed. The results showed elevated moisture in the concrete slab. 

Instead of simply recommending an alternative solution, John advised the facility manager to have core testing done on the concrete for soluble ions. She agreed and proactively spent around $4,000 on core testing. Unfortunately, when the results came back, it was decided that (at that time) we didn’t have a solution that would properly serve her environment.  

One might think that the rest of the conversation was going to be about how angry the facility manager was for “wasting” $4000, but that was not the case. She was not angry, in fact, she was grateful.  

By spending the money upfront on core testing, it prevented her from installing a $90,000 floor that would’ve most likely failed prematurely. It also saved her the additional costs and downtime associated with tearing out the floor and installing a new solution.  

The facility manager appreciated the honesty and transparency, and she is still in touch with John for other projects.  

Moisture and Concrete Slabs 

Water is an essential ingredient in concrete. There is a critical volume of water needed to “hydrate” the concrete and an excess volume of water used to make the concrete pour-able and workable. The excess water content is emitted from the slab as moisture vapor.  

In addition to the moisture vapor from the slab, there is potential for ground water to be brought to the surface. New construction will have vapor barriers installed to prevent this. In situations where a barrier was not installed or has been punctured, ground water can be wicked into and up through the concrete. As the water comes through the slab, it also brings soluble ions to the surface. 

In unsealed concrete, this process is not necessarily problematic, but when an impermeable resinous coating is placed on top of the concrete, the high concentration of soluble ions at the bond line can cause the coating to have bond failure: delaminate or blister. 

It is important to test the concrete slab to know what conditions may be present. By recognizing potential problems, testing for, and mitigating them, steps can be taken to ensure a long-lasting, successful flooring installation. 

Testing the Slab 

Dur-A-Flex provides guidance on testing concrete slabs in our Floor Evaluation Guidelines. The guidelines assist in identifying the moisture limits for each type or Dur-A-Flex flooring system.  

Dur-A-Flex recommends using in-situ Relative Humidity (RH) Testing per ASTM F-2170 as a quantitative test method. In-situ RH is the preferred method as it is not significantly impacted by ambient temperature and relative humidity conditions in the building, and therefore, likely to provide more accurate readings than Calcium chloride testing.  

An in-situ RH test is performed

Even in cases where a product can tolerate elevated levels of moisture such as Poly-Crete®, Hybri-Flex®, or Dur-A-Glaze® MVP, Dur-A-Flex may recommend that cores be taken and analyzed to determine the levels of ionic components (salts) in the slab. The combination of elevated moisture and salts could surpass the thresholds of our flooring systems, (as was seen in the Texas water treatment facility.) 

What is Core Testing?  

Dur-A-Flex offers in-house core testing using ion-chromatography technology. Using a core machine, cores are pulled and sent to our lab for testing. The rule of thumb is one core for every 1,500 square feet. For smaller areas (under 5,000 square feet) the ideal sampling will include four corners and one in the center. The core samples are examined for their content of ionic components. Based on this process’s findings and knowing the moisture readings, Dur-A-Flex can then recommend the best flooring options. 

When is Core Analysis Recommended? 

Dur-A-Flex recommends our Core Analysis Program for any concrete slabs older than a year. The testing is recommended to rule out the potential for osmotic blistering caused by higher than acceptable levels of soluble ion (salt) deposits at or near the surface. 

Core Testing

For new concrete (less than a year old) core analysis is recommended only if concrete curing compounds, hardeners, or densifiers were used. These products can be bond inhibitors by causing salt deposits at or near the surface to exceed acceptable levels for an impermeable coating. 

Third-party testing is also an option and is often advisable for comprehensive testing and transparency. These tests can identify other bond inhibitors and contaminants. Dur-A-Flex recommends having third-party tests done by a licensed petrographer. 

Potential Solutions for Excess Moisture and Salts 

Evidence of excess moisture and the presence of salts are key indicators that not all resinous flooring systems will be a fit for a facility. The results from the moisture and core testing and the needs of the space will help determine which flooring systems will work best.  

Evidence of high salts in concrete.

The choices are as follows: 

  • A breathable epoxy system 
  • An epoxy system with a moisture vapor primer 
  • A Poly-Crete based system  
  • Not installing a Dur-A-Flex Flooring System 

Yes, you read the last bullet correctly. If testing shows that the floor will most likely fail, Dur-A-Flex would prefer to have you choose a different flooring solution. It is more important to Dur-A-Flex that facilities have the right floor than it is to make a sale. 

For questions regarding core testing, please contact your local territory sales or technical services manager. They will be happy to guide you through the process.  

Contact us today.


Submitting cores for evaluation for soluble ions is an important step toward ensuring the right resinous flooring system is chosen for a facility. In addition to the Dur-A-Flex Core Analysis program, third-party testing by a licensed petrographer can be done. This will provide even further knowledge of what a concrete substrate has been exposed to. Although there are costs involved with testing, they are nominal compared to the costs associated with choosing the wrong flooring system.

Author: Jes Grant
Jes Grant is the content development manager for Dur-A-Flex. She has over 15 years of experience creating content for various technical industries, and has been featured in several publications for her writing and design work

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