Flooring Forensics: Adhesives in high-moisture environments - Aug/Sept 2022

By Don Styka

In my long career as an installer, distributor rep and technical specialist for a flooring manufacturer, I haven’t met an installer or flooring contractor who has intentionally set out to sabotage a job or create a claim situation. I have, however, seen decision making that has led to job failures that required repairs or, in some cases, total floor replacement. This is usually due to installers not reading the adhesive-label instructions and treating all water-based adhesive the same; not determining the porosity of the concrete, which has a direct effect on the trowel size and open time of the adhesive; and utilizing improperly sized or worn trowels.

The trowel is the metering device to control the amount of adhesive being applied, and if the trowel is worn, the required or appropriate amount of adhesive is not being applied (see photos below). Water-based adhesives often have different trowel requirements for porous and non-porous surfaces. Not determining if a slab is non-porous-which often requires a smaller trowel notch that leaves less adhesive-could result in the installer applying too much adhesive, creating additional problems such as adhesive dry time inaccuracies and/or adhesive displacement after heavy objects are placed on the flooring.

Adhesive selection is an important decision and a critical variable in the successful installation and long-term performance of the flooring material. The decision to switch from the recommended adhesive and not follow the manufacturer’s guidelines can impact not only the compatibility of the adhesive with the flooring, the overall working characteristics of the adhesive and the long-term performance of the flooring system but also compromise sustainability certifications and limit the amount of technical support the flooring manufacturer can provide related to the installation-such as trowel sizes, open and working time-as they won’t be familiar with a non-recommended adhesive’s performance. This may also void the customer’s floor warranty.

Even though we are in an age in which technology continues to advance more rapidly with each passing year, we are still having challenges related to properly evaluating the moisture content of the concrete slab prior to installation. This requirement has been in place for decades, with the brunt of the responsibility placed on the flooring contractor rather than a qualified, independent third-party to perform the testing. I’ve seen flooring contractors-and others-attempt to perform the required moisture testing without an understanding of the ASTM standard they are testing to. (Many manufacturers require testing in accordance with ASTM F-2170 Standard Test Method for Determining Relative Humidity in Concrete Floor Slabs Using in situ Probes or ASTM F-1869 Standard Test Method for Measuring Moisture Vapor Emission Rate of Concrete Subfloor Using Anhydrous Calcium Chloride.)

If you are agreeing to perform the moisture testing, I suggest you purchase a copy of the required ASTM standard and make sure the person performing the testing is qualified. The test results should be used to determine if a moisture mitigation system should be applied prior to the floorcovering and to help determine if there is a suitable adhesive that will perform within the conditions identified in the test results. If you do not have the experience, qualifications and resources to perform the testing, hire a qualified third-party testing professional familiar with the ASTM standards.

There have been advancements in the development of adhesives that perform with higher moisture limits. However, I caution anyone trying to avoid required moisture testing by simply using adhesives that promote a higher moisture tolerance.

Our technical support group receives calls on a regular basis asking if our adhesives will perform where moisture conditions exceed the adhesive’s published limits. The answer to this question is not a simple “yes” or “no.” One of the variables that must be determined is the age of the concrete; we anticipate moisture test results on newly poured slabs to be elevated compared to existing buildings that have been in operation for decades. The other factor that can influence the test results is the presence of a vapor retarder. Often in older buildings that have revealed higher than recommended moisture numbers, this is an indicator that there is no vapor retarder or the one that is in place has been compromised or has deteriorated over time, allowing moisture from the ground to migrate upwards through the slab.

I’ve come across specifiers researching their flooring material selection based on the moisture limits of the recommended adhesive with not as much relevance to the performance characteristics of the flooring. This type of decision is being made without the moisture test results or even the concrete being placed.

Recently, I was in a pre-installation meeting on a project site where we reviewed a pre-installation checklist to help set expectations and avoid issues that might delay or impact the installation schedule. During this meeting, the general contractor advised everyone that they have a requirement that all adhesives used to install floorcovering materials must have an RH moisture limit no less than 95%. I thought this requirement was interesting, as the project specifications and flooring contractor’s contract stated to “follow manufacturer’s guidelines,” and I didn’t see anything related to following the guidelines set in place by the general contractor. These are the types of decisions that lead to problems and the development of costly, frustrating-and avoidable-claims.

While I understand that many adhesives today will perform where higher moisture conditions exist than we’ve seen in the past, the adhesive selection should not be based solely on the moisture limit of the adhesive. As mentioned earlier, other factors must include compatibility with the flooring material.

Over time, flooring manufacturers have increased the recycled content of the flooring, often because their customers are asking for a better sustainability story that they can share with their customers and help them achieve their sustainability goals. When manufacturers submit flooring materials to be evaluated for environmental certifications, the certifications often include more than just the flooring material itself. The certification can include the impact production has on energy resources, packaging, maintenance requirements and adhesive recommendations. Choosing to deviate from one of the approved adhesives can affect the certification the customer believes they invested in when selecting the flooring materials and accessories.

Another factor should include the long-term performance of the flooring in the environment it’s been selected for. Take healthcare, for example. There is a great deal of rolling traffic and heavy point loads associated with the equipment located throughout such facilities. Using a harder-setting adhesive will help avoid adhesive displacement in these types of environments. Not all adhesives recommended for installation over concrete slabs with a higher moisture content are suitable for use with heavy rolling loads and equipment.

Don’t let the adhesive decision be based on only one factor of the project: the moisture content of the slab. Protect yourself and your customer; be diligent and review all the factors mentioned in this article when selecting the appropriate adhesive. If you are contemplating switching from the flooring manufacturer’s recommendation to a non-approved alternative with higher moisture limits, read the fine print and make sure you fully understand what coverage the adhesive manufacturer provides. Are there limitations or omissions in place, and does the warranty cover the flooring material? Is the warranty tied to moisture testing? If so, what documentation is required? Making an adhesive change might not seem like a big deal; however, it can come at a significant cost if problems develop.

Whenever questions arise or you have more than one adhesive choice, I suggest contacting the flooring manufacturer for clarification and recommendations that will protect the customer’s warranty and provide you with the appropriate information for a successful installation that will meet your client’s expectations.

When moisture testing indicates the concrete slab has high moisture, I suggest selecting the adhesive or a moisture mitigation system based on the actual test results. I say this because I have seen flooring contractors make recommendations on moisture mitigation based on what someone thought would be a safe range for a moisture mitigation product or adhesive without first performing the test. Work with your flooring manufacturer to identify the best adhesive option based on the moisture test results. Many flooring manufacturers recommend moisture mitigation systems that comply with ASTM D3010 Standard Practice for Two-Component Resin Based Membrane-Forming Moisture Mitigation Systems for Use Under Resilient Floor Coverings, and claim liability could fall to you if a problem develops or a moisture mitigation system doesn’t meet with their requirements.

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