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Are Primers Needed for Moisture Mitigation?

July 28, 2022

Yes, moisture mitigating primers are required to protect floors being installed on concrete with elevated moisture and soluble ions. Moisture mitigation is a critical step to extend the lifespan and performance of a resinous floor. Read on to learn where these compounds come from, how to test for them, and available mitigation options.

Concrete slabs are the most common substrate for resinous flooring systems. Excess moisture or soluble ions (salts) found in the concrete slab can be detrimental to the anticipated performance and longevity of the resinous floors. Therefore, all resinous flooring systems have a maximum acceptable level of moisture and soluble ions (salts).

Epoxy flooring systems have a lower threshold for moisture and salts than other resinous flooring chemistries. These limitations can be increased through the use of a moisture mitigating primer. Before installing any resinous flooring system, a critical consideration is whether or not a moisture mitigating primer will be required.

The Importance of Primers for Moisture Mitigation

Moisture mitigating primers are specifically designed to reduce or eliminate the amount of moisture which can penetrate through the pores of the concrete. The primer acts as a shield to protect the resinous flooring system. Moisture mitigating primers address moisture, and they also mitigate issues from elevated soluble ion (salts) levels.

Let’s look at moisture first:

Water is a component of concrete, and excess water is required to make the concrete pourable and workable. The porosity of the concrete slab is a direct result of the water to cement ratio in the concrete mix. The volume of moisture that can pass through a slab depends on the porosity of the slab. As the water to cement ratio increases, the porosity of the concrete increases exponentially.

Excess water vapor emitting from the pores is referred to as moisture vapor emission (MVE) or moisture vapor transmission (MVT). The moisture can be emitting from the slab’s own water content, or it can be pulled up through the slab from the surrounding ground.

High levels of moisture vapor emission from the ground can become problematic when the concrete is sealed with a resinous flooring system. The moisture becomes trapped, and hydrostatic pressure continues to build until it eventually weakens the bond between the concrete and the flooring system.  

Common moisture related failures seen in resinous floors include:

  • Failure to bond
  • Bubbles
  • Blisters
  • Delamination

Now let’s look at salts:

The salts or soluble ions found in concrete are hygroscopic, meaning they attract and absorb water. As we stated above, excess moisture is problematic for resinous floors. In addition, the combination of salts and water causes a specific failure known as osmotic blistering.

Excess salts levels on the surface of the concrete, (bond line), is where the potential issue begins. The salts can be introduced in two ways: either topically from outside contaminants such as cleaning solutions or road salts, etc., or from the underlying base materials.

Salts within the concrete are brought to the surface as they are in solution with the concrete moisture. In unsealed concrete, the water evaporates and the salts are left behind. In an attempt to equalize this salt concentration, more moisture is pulled through the concrete capillaries.

When the concrete is sealed with a resinous coating, the water will still move through the concrete capillaries to equalize the surface salts, but the moisture can no longer evaporate. This creates pressure in the capillaries which pushes on the bond line, eventually breaking and creating blisters. This failure is known as osmotic blistering and it is the most common failure associated with moisture and resinous flooring.  

Determining if Moisture Mitigation Is Required

Before the application of an epoxy (or any resinous) floor, testing should be done to determine if the concrete slab has excessive moisture or salts.

  • Most epoxies have a moisture limitation of 75% RH and 3lbs CaCl / 1000sf / 24hrs.
  • Soluble ion (salts) levels in the substrate can vary, but most epoxy systems can tolerate up to 1,600 ppm (combined Na,K,Cl).

Testing for Moisture

There are several methods available for moisture testing, two common ones are:

  • Slab Moisture Testing (ASTM F2170 – In Situ RH)
  • Calcium Chloride (ASTM F1869)

Dur-A-Flex recommends using In-situ 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 thus likely to provide more accurate readings.

Calcium chloride (CaCl) limitations are still specified however, this testing is not recommended for moisture testing. The results will differ based on the environmental factors at time of testing.

Testing for Soluble Ions

Taking core samples of the concrete and sending them for Core Analysis is the most reliable way to test for soluble ions. Dur-A-Flex offers this service in–house, but there are also third-party options available. (For an in-depth analysis of other components including possible contaminants, Dur-A-Flex recommends all concrete be tested for quality by a licensed petrographer).

If pre-installation testing reveals moisture and or salts outside of the above parameters, then a moisture mitigating primer should be used. 

Outside of testing, there are also ways to safely assume a primer should be applied:

  • Green concrete (newer than a year)
  • Slab discoloration
  • Darkness at the crazing
  • Porous or rough concrete
  • Evidence of salts on the surface of the concrete*
  • High water tables*
  • Previous coating failures – particularly osmotic blistering*

* These signs may be indicative of moisture and salts levels that are beyond the limitations of epoxy primers. Consider switching to cementitious urethane coatings such as Poly-Crete. Testing will confirm.

Choosing the Right Moisture Mitigation Product

Choosing the right moisture mitigating product for your epoxy floor system will depend on the results from your specific slab. Each primer will come with its own list of benefits, i.e. tensile strength, compressive strength, etc. The two key elements to look for are the Moisture Vapor Emission Rate (MVER) and the Soluble Ion Tolerance.

Dur-A-Flex has two exceptional options for epoxy moisture mitigating primers: Dur-A-Glaze MVP & Dur-A-Glaze MVP3.

Dur-A-Glaze MVP Primer is a two component, 100% solids moisture mitigation system. It reduces moisture levels as high as 99% RH and 20 lbs CaCl /1,000 SF /24 hrs to less than 3 lbs /1,000 SF / 24 hrs. Its soluble ion tolerance is 1,600 ppm (combined NA, K, Cl).

Dur-A-Glaze MVP3 Primer is formulated specifically to aid in higher moisture epoxy system installations than Dur-A-Glaze MVP. Dur-A-Glaze MVP3 has a faster cure time and features low permeability in compliance with ASTM F3010-18.

Dur-A-Glaze MVP3 Primer is a clear, 100% solids epoxy moisture vapor barrier and primer.  reduces moisture levels as high as 99% RH and 24 lbs CaCl /1000 SF/ 24 hours down to ≤3 lbs CaCl /1000 SF / 24 hours. Its soluble ion tolerance is 2,400 ppm (combined NA, K, Cl).

See a side by side comparison of these primers.


Concrete slabs with elevated levels of moisture and or salts should have a moisture mitigating primer applied before the installation of any resinous flooring system. Start a conversation with us, we’ll help you identify which moisture mitigating primer is recommended for your specific project. Our territory sales managers are also available to answer any other questions regarding Dur-A-Flex’s flooring solutions.

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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