A Floor Professional’s Guide to Testing for Acceptable Concrete Moisture Levels

When concrete is first poured, it contains gallons of excess moisture that have to evaporate before a floor covering can be installed on top.

“URGENT HELP!!”

The above was part of a headline on Flooring Forum. The post read:

“Our concrete slab was poured in December as our house is completely new. We are now getting engineered wood floors installed…. I am concerned that there may be a moisture problem, but the guys who will be installing the floors told us we do not need to check the moisture content of the concrete slab. Especially since we will be using a glue with a moisture barrier incorporated into it. Do we need to push to get the moisture [levels] checked out before we proceed?”

How would you reply?

Here at Wagner, we would say, “Why risk the chance of a moisture issue? Like many other types of flooring, engineered wood is sensitive to moisture.”

That moisture “barrier” is probably more accurately called a “retarder”—something that slows, but not stops, the transmission of moisture. We’ve seen many times when too much faith was put into an expensive product, and then when it fails, all that the customer gets for their warranty trouble is another bucket of the adhesive—not the floor that needs replacing or the labor that goes along with it.

In other words, not checking the concrete for moisture could easily lead to flooring failure—and money and time wasted on repairs!

So, let’s spend some time understanding moisture’s impact on concrete. This way, you can be sure your concrete slabs are at an acceptable moisture level before you install a floor. We’ll also see how the relative humidity test is the best way to check those levels.

We’ll cover:

• The fundamentals of concrete and moisture
• Standards for concrete moisture testing
• Why test concrete moisture levels per ASTM F2170
• Rapid RH, the best option for concrete moisture testing
• How Rapid RH is making a difference

First, let’s address the basics about how moisture affects concrete.

The Fundamentals of Concrete and Moisture

Moisture typically occurs in concrete as relative humidity. This is moisture in vapor form rather than liquid form.

When concrete is first poured, it contains gallons of excess water. In fact, a truckload of concrete has an estimated 320 gallons of water!

The mixture of cement, water, and aggregate causes the concrete to harden. But that doesn’t mean it’s dry!

It’ll still contain a lot of moisture that has to evaporate over time.

As it does so, it forms a moisture gradient with more moisture deep within the slab and less moisture near the surface.

That excess moisture can affect a floor installed above the concrete slab. “Floor coverings often fail due to unsuitable concrete moisture levels beneath them or arising out of the concrete substrate,” says a technical bulletin about relative humidity testing and concrete.¹

For a hardwood floor, that could look like warping of the boards, including cupping and buckling. With other types of flooring, such as engineered wood, laminate, and vinyl, excess moisture could cause staining or sweat. Or adhesives might fail, leading to:

• Delamination
• Peeling
• Blistering

And finally, if a carpet is installed on top of the concrete, moisture can become trapped between the slab and the carpet. Mold and mildew can grow in that spot, causing health hazards and odors.

The person on Flooring Forum was right: her situation was urgent. Not testing for moisture would put her new floor at risk!

The standards for proper concrete moisture testing help avoid these risks and the associated issues.

Standards for Concrete Moisture Testing

The calcium chloride test measures the amount of moisture that evaporates from the surface of the concrete within 24 hours, but it doesn’t provide an accurate picture of the moisture deep within the slab.

Two standards are particularly pertinent to concrete moisture testing today:

• ASTM F1869: The calcium chloride test
• ASTM F2170: The relative humidity test

These standards are beneficial to both flooring professionals and their clients. They provide guidelines that ensure a successful installation, so you can leave the jobsite satisfied with a job well done (and less chance of damage later), and the clients will trust your work and enjoy their new flooring.

Let’s take a look at these two standards.

ASTM F1869: The Calcium Chloride Test

The calcium chloride test has been a standard in the concrete industry for years. But just because something has been around for a while doesn’t mean it’s the most accurate option.

Calcium chloride measures the moisture vapor emission rate (MVER), the amount of moisture that evaporates from a concrete slab within 24 hours.

But here’s the problem with that.

As we’ve already noted, concrete contains a lot of excess moisture when it’s first poured. Most of that moisture hides deep within the slab.

The calcium chloride test only measures moisture evaporating off the surface. As a result, it only indicates the concrete’s moisture condition within the first ½ to ⅔ of an inch.

Meanwhile, it misses the moisture hidden deep in the slab, which will later reach the surface, wreaking havoc.

Because of the limitations of the calcium chloride test, ASTM F1869 no longer permits its use for lightweight concrete. The relative humidity test is a much better option—the test governed by ASTM F2170.

ASTM F2170: The Relative Humidity Test

ASTM F2170 governs the in situ relative humidity test, which provides the deep readings needed to get an accurate picture of the concrete’s moisture condition.

Rather than testing the concrete only in the top inch or less, the relative humidity test involves taking measurements at 40% depth of the concrete, which gives a much better idea of how much moisture is hidden deep in the slab and will still evaporate from the surface.

Key components of the standard include:

• Using test probes that have NIST-traceable calibration (section 6)
• Having the environment at service temperature and relative humidity at least 48 hours before testing (section 9)
• Placing 3 tests for the first 1,000 square feet and 1 test for every additional 1,000 square feet (section 10)
• Allowing the probes to equilibrate for 24 hours (section 10)
• Drilling to 40% depth (if drying the slab from one side) or 20% depth (if drying from both sides) (section 10)

The standard also recommends that, in general, concrete should have a relative humidity reading of 75% or less before installation. This number, however, will vary depending on the flooring manufacturer’s requirements.

Why Test Concrete Moisture Levels Per ASTM F2170

The Rapid RH test allows you to measure the concrete at 40% depth per ASTM F2170. This way, you can confidently move forward with the floor installation.

Following ASTM F2170 for the relative humidity test may mean the difference between success and failure in a flooring installation project. It could affect your whole business, too.

When you make sure the slab is within a certain relative humidity range, you’re protecting the floor and the hard work, time, and money you’ve put into it. When its moisture levels match the environment and remain consistent, you’re much less likely to get calls months later with complaints about cupping, delamination, or any other problems mentioned above.

You’re also showing thoroughness and professionalism, which no doubt will build trust with your customers. When they know that you want the best for them and that you follow industry guidelines, they’re much more likely to choose you again or promote you to others.

In short, following these standards is wise business policy.

And finally, these standards relating to your industry, including ASTM F2170, can protect you against problems you didn’t cause and resulting legal repercussions. If, perchance, a customer blames you for a flooring issue—a result of their negligence—you’ll have the evidence to show you did your part.

So, you’re convinced of using in situ relative humidity testing. Which one do you use?

The Best Option for Concrete Moisture Testing

Rapid RH® L6 is Wagner Meter’s in situ relative humidity test, which aligns with the ASTM F2170 standard. Its probes are NIST-calibrated according to the standard. With it, you can drill to 40% depth of the slab and detect hidden moisture that a surface test wouldn’t allow you to.

So why choose it?

It’ll save you time.

ASTM F2170 only requires test probes to equilibrate for 24 hours, unlike the 72 hours required for the calcium chloride test. And after that initial equilibration period, Rapid RH devices will give you readings within 2 minutes.

You can leave the sensors in the slab to get additional readings anytime you need them.

It’ll save you money.

The Rapid RH L6 has the lowest cost per test of relative humidity tests. And the other financial benefit is that you’ll have a much higher chance of a successful installation—the first time. No going back for flooring replacements or repairs due to moisture issues.

It’ll give you confidence

You won’t be relying on guesswork for your project. You’ll know for certain your slab is ready for installation.

And this confidence will spill over to your clients. They will trust you, and your reputation for quality and diligence will spread.

But don’t take it from us. Let’s see how Rapid RH benefits a flooring company in Maryland, USA.

How Rapid RH Is Making a Difference

Robert Bode is the vice president of operations at CB Flooring, a company based out of Columbia, Maryland, that designs, supplies, and installs commercial flooring and tile. Needing to switch from the calcium chloride test and meet the ASTM F2170 standard, CB Flooring decided to make Rapid RH part of their process.

“I have seen all kinds of moisture testing methods that state they meet ASTM 2170, but we feel these Wagner probes provide the most accurate readings in the industry,” Robert shares.

His team appreciates that the probes are set in the concrete because it “gives us the assurance that our readings are more accurate than other methods where the probe is connected to the reader and placed in a sleeve.”

And with those accurate readings comes the greatest benefit of successful installations. Robert says, “We have yet to have a failure since we started using [Rapid RH] and would highly recommend them to anyone that asks.”

Relative Humidity Testing—A Peace Worth Investing In

You could risk not testing concrete moisture before installing a floor. But it’ll be a gamble—with some high stakes.

If the concrete contains excess moisture, you could be looking at:

• A failed floor
• Costly repairs and replacements
• Disappointed customers
• A poor reputation

Wouldn’t it be better to avoid the risk and worries altogether? Proper concrete relative humidity testing will assure you that you’ve done all you can to get the slab to acceptable RH levels and prevent flooring damage.

The peace you’ll experience is something worth investing in. Learn how to make that a reality for your business with the Rapid RH line of concrete moisture testing.

1. “ASTM F 2170 RH (Relative Humidity) Testing Protocol,” AC Tech Technical Bulletin, no. 18.

Jason Spangler

Jason has 20+ years’ experience in sales and sales management in a spectrum of industries and has successfully launched a variety of products to the market, including the original Rapid RH® concrete moisture tests. He currently works with Wagner Meters as our Rapid RH® product sales manager.