Concrete Moisture Testing for Residential Flooring

When you install residential flooring over a concrete slab, there’s one step that is crucial to ensure a beautiful, long-lasting floor.

That step is testing the moisture condition of the concrete. Unfortunately, it can get overlooked in a residential setting. If you don’t do it before you install the finished floor, you risk a moisture-related flooring failure. And that means the possibility of unhappy customers, expensive callbacks, and even harm to your reputation.

So, let’s take a close look at:

● Why concrete moisture testing is so important

● Two common methods of testing for moisture in concrete

● How to use the results of your concrete moisture test

Why Is Concrete Moisture Testing Important?

Concrete can fool you. While the surface of a concrete slab may seem perfectly dry, the inside of the slab can tell a different story.

Never assume concrete is dry enough for floor installation simply by looking at it. Water is one of concrete’s three main ingredients, along with cement and aggregate. After the initial pour, the water within the slab will gradually make its way to the surfaces and evaporate. As the slab dries, a moisture gradient will form, with the levels of moisture deep within the concrete being higher than at the surface. This moisture gradient is the reason you cannot go by appearances. You must test for moisture to make the right decision about when it’s safe to install. Otherwise, you risk a whole host of problems. Excess concrete moisture will mess with adhesives, and in the case of wood flooring materials, it could cause issues such as buckling, cupping, and warping. It could even lead to the growth of mold or mildew.

So, what are your options for testing concrete moisture levels?

Two Common Methods of Testing for Moisture in Concrete

In residential settings, you have two primary options for moisture testing. They are relative humidity (RH) testing and the use of a concrete moisture meter.

Relative Humidity Testing

With this method of testing, you drill holes to a specific depth and place RH probes in the holes. After waiting 24 hours, you can take RH readings for an accurate picture of the overall moisture condition of the slab.

Important tip: Always adhere to ASTM F2170 guidelines to ensure test results you can rely on.

The Rapid RH L6 system by Wagner Meters makes the RH test especially fast and easy to perform. With the L6 system, a smartphone app—the DataMaster L6—is also available to simplify the collection and storage of your RH data. Plus, other options and accessories can automate the entire testing process.

Testing with a Concrete Moisture Meter

For residential installations, you may prefer a handheld moisture meter over RH testing. It’s a fast and non-destructive way to learn about the amount of moisture in the slab. But keep in mind that you’re only measuring moisture in the top ½” or 1” of the slab, and the ASTM standards don’t recommend you use these measurements to make a final installation decision.

Be sure to use a meter that’s specifically calibrated for concrete, such as the C555 concrete moisture meter by Wagner Meters. The C555 can identify moisture “hotspots” for strategic placement of RH probes.

How to Use the Results of Your Concrete Moisture Test

The primary purpose of moisture testing, of course, is to inform your decision about when to install.

Many flooring manufacturers specify acceptable levels of concrete moisture for their flooring product. You’ll want to follow these specifications so you don’t risk a problem with moisture.

The results of your testing should also inform any necessary moisture mitigation measures if you find that moisture levels are too high. Alternatively, you could consider a different flooring material that’s less susceptible to moisture issues.

In a Nutshell

Whenever you install flooring over concrete, always remember to test for moisture. The RH test is preferred for accurate, reliable test results.

Some businesses without another option default to the concrete moisture meter. And though testing with a concrete moisture meter is not an accepted ASTM method, it may improve the probability that the moisture content is acceptable for the installation.

By carefully considering the moisture condition of the concrete slab, you will be able to avoid potential problems caused by excess moisture. ■

For more information about moisture testing in concrete, visit WagnerMeters.com or call Jason Spangler toll-free at (844) 533-9100.