How Moisture Impacts Floor Coverings Over Concrete

Imagine walking down the aisle of a flooring store with your customer, showing them all the possibilities for their home. Glistening hardwoods, cozy carpets, regal tile…

But this customer has a concrete subfloor. Could moisture in the concrete affect certain types of flooring installed over top? How?

That’s where this article comes in. Concrete can affect a floor covering installed over it, and it has to do with moisture.

Let’s explore this topic with the following points:

• The basics of floor coverings and moisture
• Moisture’s impact on flooring systems
• Proper vapor retarders under concrete
• Testing for moisture
• Tips and techniques to stop floor covering failures

The Basics of Floor Coverings and Moisture

Concrete is the base on which many types of floor coverings are placed. This includes ones like:

• Carpet
• Hardwood
• Engineered hardwood
• Laminate
• Vinyl
• Tile

Choosing your floor covering might be the fun part, but if the concrete isn’t dry or the flooring isn’t installed properly, you could be setting yourself up for failure.

This is because areas of the building or room that are prone to moisture could damage or destroy flooring in a matter of weeks or months. And there are many areas in a building where moisture tends to lurk, such as bathrooms, kitchens, and concrete floors.

Let’s take a look at how moisture can impact a floor in the context of concrete.

Moisture’s Impact on Flooring Systems

In short, moisture has the potential to damage an astonishing variety of flooring systems. Here’s what happens.

After concrete is poured, it goes through the curing process and then continues to dry. A common rule of thumb is about a month of drying for every inch of slab thickness under good conditions (enclosed, with the HVAC running), but actual drying times vary widely, which is why the slab should be tested. Then, a floor covering like hardwood, carpet, or tile is installed over it.

However, if the concrete hasn’t dried sufficiently before the floor covering is laid, there may be problems down the road. Moisture from deep in the concrete will continue to rise to the top, and depending on the flooring, that moisture will absorb into it or collect under it.

These two outcomes of moisture releasing from the concrete can cause quite a few problems in the flooring, including:

• Adhesive breakdown. Adhesive breakdown in flooring can be caused by alkaline salts in the concrete. As moisture rises to the surface of the concrete, the alkaline salts that move with the moisture work their way between the concrete and the flooring. They break down the adhesive, causing the flooring to pop up. This is unsightly and can present a tripping hazard. It also compromises the integrity of the flooring. Bubbling or ripples in the floor covering are tell-tale signs that moisture has gathered in the flooring, pushing it up in that area.
• Warping or distortion. This is especially common with wood flooring, which is very susceptible to moisture. Wood readily absorbs moisture, so the boards can twist, cup, bow, or crack in response.
• Mold and mildew. Two common problems in carpeting and tile, mold and mildew can grow under or in the flooring. They are caused by constant dampness from moisture being trapped under the flooring. A musty odor that won’t go away after cleaning, or black spots on the floor, can be signs of mold. It should be dealt with as soon as possible because it can cause illness.
• Staining or discoloration. White is a common stain color that appears on tile grouting or mosaic flooring. This is due to efflorescence: the salts in the concrete rise to the surface with the moisture and then get deposited there when the moisture evaporates. This residue can stain or damage the floor’s appearance.
• Re-emulsification of the adhesive. Re-emulsification is when the adhesive gets soft again and doesn’t bind the floor covering to the concrete. Excessive moisture passing through the concrete can cause this.

As you may have noticed, these problems are all a result of moisture (and with it, alkaline salts) passing up through the concrete and into the adhesive or floor covering. One way to help prevent this is with a proper vapor retarder under the concrete.

Proper Vapor Retarders Under Concrete

A vapor retarder is a plastic sheet placed under the concrete to keep moisture from the ground from moving up into it. Vapor retarders don’t block all moisture, which is why they’re rated by their permeance. Under ASTM E1745, the standard for under-slab vapor retarders, Classes A, B, and C differ in strength and puncture resistance, and all three must have a permeance of 0.1 perms or less.

Permeance, expressed in perms, is a measure of how much water vapor can pass through the vapor retarder over a specified amount of time. The lower the perm rating, the less moisture is able to get through.

The vapor retarder itself should be at least 10 mils thick to avoid tearing, according to the Guide to Concrete Floor and Slab Construction published by the American Concrete Institute. If you’re working with a lot of sharp points, it may need to be even thicker. Once it tears, its ability to prevent moisture is compromised.

Even with the benefit of a vapor retarder, knowing how to minimize the effect of moisture on flooring systems is worthy knowledge.

Concrete Moisture Testing

The biggest step in stopping flooring damage due to concrete moisture comes even before the installation of the flooring. This is the pre-testing of the concrete itself.

If the vapor retarder isn’t working properly, or the concrete is not truly dry yet, moisture will continue to rise to the surface of the concrete. This moisture will collect under or seep into the flooring over top, often severely damaging it.

The problem is, you usually can’t tell moisture is rising to the concrete’s surface just by looking at it. To see what’s really going on beneath the surface, you have to conduct a moisture test.

If you’re testing with a concrete moisture meter, the Wagner Meters C555 concrete moisture meter is accurate and easy to use. Just place the meter’s sensor pad on the surface to get fast results.

However, check with the manufacturer of the floor covering first. A concrete moisture meter is a screening tool (covered by ASTM F2659), and many flooring manufacturers require in-situ RH testing per ASTM F2170 instead. Make sure the manufacturer will honor its warranty if you use a moisture meter, and if it will, check that your readings are within its specifications.

If you’re conducting an RH test, Wagner Meters’ Rapid RH gives you the ASTM F2170 result in 24 hours, and early readings can give you an indication sooner.

The Rapid RH test involves drilling strategically placed holes in the concrete and inserting small in-situ sensors into them. The sensors measure the relative humidity in the concrete. Used with the Wagner Meters’ DataGrabber^® and the accompanying DataMaster™ L6 app, you can collect the readings from the Rapid RH test. Once collected, you can organize, analyze, and make reports of the data.

What’s more, with the True Remote Monitoring™ system, you don’t even have to be on the jobsite to collect the data.

This data can help you determine whether it’s safe to install flooring without the risk of ruining it or whether there’s too much moisture rising from the concrete to do so.

Tips and Techniques to Stop Floor Covering Failures

Here are some things to keep in mind before, during, and after installing a floor covering over concrete:

Choose Moisture-Resilient Flooring

Oak floors probably aren’t the best option in moisture-prone areas like bathrooms or kitchens because they absorb moisture so easily. Instead, select flooring types that are more resistant to leaking water. These are usually non-wood floors, such as tile (porcelain, ceramic, vinyl, etc.) or vinyl (luxury or sheet).

And if you’re installing flooring where spills happen but are cleaned up quickly, laminate and engineered hardwood can work.

Install Properly

Some types of flooring, like laminate, require a gap between the edge and the wall, and other types may require certain practices during installation. With any type of flooring, be sure to follow the manufacturers’ installation instructions.

Above all, check that the concrete is dry before installing the floor. You can do this with a concrete moisture meter or RH testing:

Rapid RH testing: If you’re preparing to install new flooring over concrete, use Rapid RH to check the concrete’s relative humidity. In 24 hours, you’ll have an ASTM F2170 reading to help you decide whether you can safely install flooring.

DataGrabber: This optional tool automatically records Rapid RH readings while you’re away from the job. It connects via Bluetooth^® to your smartphone, so you don’t have to collect each reading by hand.

True Remote Monitoring: If you are using the Rapid RH, the True Remote Monitoring system will take it to the next level. This system allows you to be anywhere in the world and receive relative humidity readings of the concrete.

Perform Regular Maintenance

Installing the floor is only the beginning. Advise the owner to perform regular maintenance to ensure that the floor stays in peak condition and to stop any moisture problems that may rear their ugly heads. Here are some important tips:

• Sweep and/or mop floors regularly.
• Clean up spills or accidents immediately.
• After a heavy rain, check for leaks and excess moisture.

You may also want to include an advanced tool as part of your installation package to prevent unwanted problems down the road. That tool is Floor Sentry^®, a small, embedded tool that monitors temperature and relative humidity conditions in flooring.

If conditions go outside the range you set, Floor Sentry alerts your clients so they can take action before the floor is damaged.

Choose Wagner

Because concrete is made with water, moisture will always be a potential issue when you’re installing a floor covering over top. It can seep into the flooring and cause it to warp or separate. It can collect under the floor and cause mold or other structural damage.

By making sure the concrete is dry enough to install the floor covering and choosing moisture-resistant floors, you can minimize or eliminate these issues.

Make your proactive steps even easier with a Wagner Meters product to monitor or measure the moisture content. Contact us for advice and help with concrete moisture testing.

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Last updated on October 20th, 2026