Moisture’s Effect on Adhesive Bonding in Concrete Floors

Wood floor adhesive

Moisture can affect the adhesives used by flooring installers to install floorboards.

Imagine taking time to install a beautiful vinyl floor only for your client to call you months later about it bubbling.

As you return to the site to inspect the problem, you notice that excess moisture has weakened the floor adhesive. This caused the flooring to bubble.

Adhesive failure due to excess moisture is a common problem in the flooring industry. But you don’t have to let it happen to you. We’re here to help you prevent moisture from weakening adhesives.

Let’s explore:

The Source of Excess Moisture

Concrete slabs contain moisture even after they cure. This excess moisture can weaken your flooring adhesive. While much of the water used in concrete will bond with the cement mix1, the moisture that’s left over is usually deep within the concrete slab. Over time, it’ll rise to the top of the slab and evaporate from the surface.

This is why concrete isn’t necessarily dry even if it is hard and “cured”—or even if it looks dry.

Most of this moisture comes from the excess water that was originally mixed with the cement. However, as a porous material, concrete can also absorb moisture from external sources like flooding and leaky roofs, or the ground if there’s not an intact vapor retarder.

Regardless, it’s important to understand how much moisture your concrete contains so you know when it’s safe to apply flooring adhesives.

Effects of High Moisture on Adhesive Bonding

Loose wood floor tiles due to moisture

Adhesive failures can cause loose floorboards.

Excess moisture may cause pH levels to rise, dissolving the adhesives over time. This happens when the moisture in the concrete rises to the surface of the slab and combines with alkali salts.2 The alkali salts cause the pH of the water to become more alkaline, leading the flooring adhesive to break down.3

Fortunately, there’s a way to minimize the chances of moisture harming the adhesive.

Prevention of Adhesive Failures due to Excess Moisture

You can help prevent adhesive failure by monitoring the moisture in your concrete subfloor. This is done with concrete moisture meters and relative humidity (RH) testing.

Concrete moisture meters can assist in determining how moisture varies across the surface of the slab. The ASTM F2659 standard recognizes the use of moisture meters to determine where to place additional RH tests.

Many installers also choose to use it because it can get the results quickly and without damaging the concrete’s surface. If you want to use a concrete moisture meter to make the final decision about whether it’s safe to install the floor covering, check for two things:

  1. That the floor covering manufacturer recognizes the use of moisture meters
  2. That your meter readings match the readings in their guidelines

Keep in mind that many floor covering manufacturers do not recognize the use of concrete moisture meters for the final decision.

RH testing is a testing method that is accepted by the ASTM F2170 standard. It involves placing in situ probes into a slab at 40% depth to get an accurate picture of how much moisture the slab contains. Per ASTM F2170 standards, once the probe has been placed, it needs to equilibrate for 24 hours before you can get a reading.

ASTM standards say you can safely install your floor covering if your concrete subfloor has an RH of 75% or less. However, many flooring materials and adhesives can withstand much higher levels.

That’s why it’s best to go by manufacturer guidelines.

Once you’ve installed the floor, you can continue to protect your floor covering installation with moisture monitors and ambient sensors.

Here are some options Wagner Meters offers.

Wagner Meter Products for Moisture Management

Rapid RH sensor in concrete

Rapid RH probes are placed deep within a slab of concrete to get more accurate readings.

For relative humidity testing, Wagner Meters offers the highly accurate Rapid RH® with three different ways of recording the data, depending on your needs. You can choose from the following:

  1. Hands-On Monitoring: This system allows you to take manual readings. It’s a great option for those who like to record measurements themselves.
  2. Automatic On-Site Monitoring: This system sends in situ probe readings directly to the DataMaster™ app on your phone so you can access the readings as long as you’re in range of the jobsite.
  3. True Remote Monitoring™: With this system, you don’t even have to leave your house to get readings. It sends them directly to the Floorcloud® app on your phone—no matter where you are. This can save you a lot of wasted trips to the jobsite.

On top of the Rapid RH family, we’ve got the C555 concrete moisture meter. As one of the fastest and most accurate moisture meters on the market, it’s a great tool for any flooring installer to have. By itself, it can give you a better idea of the moisture levels of your subfloor. And, when paired with the Rapid RH, it provides a great solution for quickly identifying high-moisture areas to place your Rapid RH probes.

If you’re working with wood floors, you can add an extra measure of floor protection with our in-floor data logger, Floor Sentry®. It just needs to be installed on the underside of a floor plank. It’ll help clients keep an eye on the moisture levels of their floor covering, telling them when it’s absorbing excess moisture that could harm the adhesives.

Let’s talk about how you can use all these tools during the moisture measuring process.

Moisture Measurement During Installation

To measure for concrete moisture during floor installation…

  1. Check that the ambient temperature and humidity are being maintained at in-use levels.
  2. Locate high moisture hotspots with a concrete moisture meter.
  3. Drill holes in those areas and place RH probes.
  4. After 24 hours, take the RH readings.
  5. Determine whether the readings are acceptable for your flooring adhesive.

See “How to Test Moisture in Concrete Floors” for more details about the measurement process.

For now, we’ll turn to some steps for post-installation moisture monitoring.

Moisture Monitoring After Installation

If you are using wood for your floor covering, an in-floor data logger, like our Floor Sentry, allows your clients to monitor the moisture levels of the floor covering after you’ve installed it.

Here’s how you use it:

  1. Take one of the floorboards and, with the given template, use a router to carve out a section of its underside.
  2. Place the Floor Sentry into the space you just carved out.
  3. Install the floorboard with the Floor Sentry device on the underside.
  4. Instruct your client on how to connect the Floor Sentry to the Wagner Sentry® app to receive moisture readings on their phone.

With the app, your clients will get regular reports on their floor’s moisture levels. This can help them detect moisture problems before they occur or cause more issues.

In this way, Floor Sentry can protect your work and build your reputation. Customers will come to know you as a flooring professional they can trust to install long-lasting, beautiful floors.

No More Flooring Adhesive Failures

With the appropriate moisture testing, you can rest easy knowing your flooring coverings are safe from damage. And the best news is, with Wagner Meter products, checking moisture levels is easier and more accurate than ever before!

Visit our shop to find the options that best suit your business.

  1.  Scott Tarr and Roland Vierra, “The Solution is Avoiding the Solution,” Hardwood Floors Magazine. 
  2.  Tarr and Vierra. 
  3.  Ibid. 

Last updated on December 10th, 2024

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