Signs a Concrete Floor Has Moisture Issues

The majority of commercial and industrial buildings are constructed with a concrete substrate laid over prepared soil, called slab-on-grade.

Floor covering manufacturers, whether producers of tile, wood, carpet or high-performance floor coatings, publish the maximum allowable moisture content of the concrete over which their flooring products can be installed, based on results of various ASTM test methods.

Floor moisture and moisture vapor can be cause for concern, whether the slab is newly poured or many decades old and regardless of location. Concrete science is still evolving. While the industry doesn’t have all the answers, it can be said that moisture issues in concrete floors tend to arise from one of two sources:

1. The concrete mix itself, in the event the slab is insufficiently cured or is otherwise holding moisture

2. The soil under a slab-on-grade, in the event of an improperly functioning vapor barrier

Water is an important component of any concrete mix. Newly poured concrete, given enough time, will eventually release sufficient moisture during the curing process to proceed with building construction and floor covering or a resinous floor coating system installation.

Moisture Still Present

Unfortunately, a concrete surface can easily give a false impression of being dry enough despite containing moisture well above the allowable limits. That is because even once the slab has cured, it’s never completely free of moisture.

Concrete is porous by nature and, even though the moisture near the surface of the concrete evaporates as it cures, moisture from below the concrete or within the concrete will tend to osmotically migrate up through the concrete capillaries, to escape through the path of least resistance. This process is referred to as moisture vapor transmission (MVT).

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Moisture vapor can be measured in terms of concrete relative humidity (RH) or in terms of the rate at which the vapor is moving through the concrete. Flooring manufacturers’ suggested test methods and limits should be adhered to for best outcomes.

In the event that test results exceed the recommended moisture limits, some manufacturers offer effective MVT control solutions for use with their flooring products.

Dangers of Moisture Vapor Transmission

Some of the potential flooring issues that can result from excessive moisture vapor transmission are:

• Delamination or bonding failure of a floor covering due to the highly alkaline liquids that can condensate underneath

• Cracking or bubbling of a floor covering or resinous floor coating system

• Development of uneven walking surfaces, creating slip-and-fall hazards

• Reduced lifespan of the flooring material; damaged aesthetics

• Invalidation of floor covering warranty, depending on MVT limits

• Eventual deterioration and crumbling of the concrete substrate

• Development of mold or pathogen growth either on top of the concrete slab or beneath the flooring material

Repair and remediation of concrete floor moisture conditions can be costly, and may include:

• Removal and disposal of damaged floor covering

• Replacement of flooring, using MVT mitigating systems

• Mold inspection, remediation throughout the facility; certification of eradication

• Replacement of concrete slab

Excessive concrete floor MVT can lead to more frequent, expensive repairs than anticipated, requiring production downtime and potential loss of revenue.

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Recognizing the Signs of Concrete Moisture Issues

The earlier any problems are noticed, the sooner you can act and help mitigate adverse outcomes. Vigilance and regular monitoring of the floor condition is critical.

Remember, your flooring can look fine, yet still be in the early stages of developing moisture issues.

Observable Signs to Look For

When inspecting your flooring for MVT, ask yourself:

• Are there any damp spots on the floor or areas where you can see darker discoloration?

• If your flooring is tile or other material that required the use of an adhesive and/or grout during installation, do you notice any loose pieces or see any signs of delamination?

• Can you observe any cracking, bubbling, lifting or peeling of the floor surface?

• Is there any white residue coating the floor, indicating alkali/salt deposited by condensed moisture vapor?

• Do you see any black stains on the floor and/or walls? Is there a musty or mildew odor in the room or in any particular area?

If you answer yes to any of these questions, you may want to consider moisture vapor testing. There are several techniques and tests available to do it yourself or hire a professional.

When to Test for Moisture in a Concrete Slab

In an ideal world, every slab would be tested for moisture prior to the installation of a floor covering.

In terms of new construction, the slab should be tested after it has cured and prior to the installation of a floor covering. If excessive moisture is present, it needs to be addressed. If left to fester, it will cause problems over time, which can lead to delamination and require a complete re-installation, etc.

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