Why Measure pH and RH Levels in Concrete Before Installing Floors?

Sports FloorFlooring contractors who work with concrete floor slabs may need to take both pH (potential hydrogen) and RH (relative humidity) levels of concrete into serious consideration before attempting to install any flooring materials or risk costly project failures.

What Is the pH Level of Concrete?

Freshly-poured concrete has a pH level of 12 to 13. The calcium hydroxide reacts with carbon dioxide in the air, forming calcium carbonate, which reduces pH levels at the surface of the concrete. For concrete and floor installations, many adhesive manufacturers require pH levels of 10 or below.

The Basics of pH in Concrete

When water dissolves additives in liquid, the liquid will have either an acid or alkaline (base/basicity) content.

Concrete manufacturers mix aggregate and cement with water to ensure its strength and stability, however the pH of the water in the mix changes during the process. When applying adhesives to bond a floor covering to concrete, flooring installers must adhere to manufacturer pH guidelines. If they don’t, the adhesives, finishes, and flooring materials they use will likely debond, blister, stain, or suffer other major performance problems.

In addition, concrete additives, along with the natural hydration process of the concrete, introduce some level of either acid or base to the existing moisture of a concrete slab. Acids form hydrogen (positive ions) when added to water and bases form hydroxide (negative ions). Neither one is inherently good or bad, but they both have different atomic reactions when added to water.

In general, pH readings measure acidity versus basicity. The pH scale ranges from 0 to 14. For example, the pH of battery acid is zero, while liquid drain cleaner has a pH of 14. In relation to concrete and floor installations, many adhesive manufacturers require pH levels of 10 or below. Unfortunately, freshly-poured concrete has a pH of 12 to 13. This pH is due to the formation of calcium hydroxide during the hydration process. The calcium hydroxide, in turn, reacts with carbon dioxide in the air, forming calcium carbonate, which reduces pH at the surface.

RH – The Reliable Indicator of Moisture inside the Concrete

TH-200 Thermo-HygrometerOnce poured, the top surface of concrete slabs will exhibit a moisture layer that belies the actual amount of moisture in the slab. That’s why it’s necessary to test inside the concrete first before laying the floor covering so the appropriately selected adhesives will bond as they should.

This “inside” test, known as the in situ RH test, is a scientifically proven method indicating the true moisture condition of the concrete slab. Studies have clearly demonstrated the test’s reliability and accuracy. Moving ahead with a flooring installation while lacking reliable information about the slab’s moisture condition would be risky. If the concrete slab is not allowed sufficient time to dry before the flooring is installed, the litigation and repair costs due to a moisture-related flooring failure could spiral out of control.

Keep in mind that concrete and adhesive manufacturers produce guidelines that installers must consider before proceeding with a certain product. Changes in local weather, humidity, and seasons can also influence the outcome.
Thankfully, simple assessment tools exist for both RH and pH.


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Rapid RH® Concrete Moisture Testing System

Wagner Meters has developed accurate and cost-effective digital technology, known as the Rapid RH®, for fast, cost-effective RH readings. Our calibrated RH probes can be installed by contractors to 40% slab depth (of a slab drying from one side) and easily read data from a digital, wireless reader (by using the DataMaster™ app, which is compatible with most mobile devices).

The Rapid RH is specifically designed to make it easy to take multiple measurements of each test location and accurately determine when a concrete slab has reached an appropriate RH moisture condition for the flooring to be applied. The Rapid RH Starter Kit is a good way to get testing.

Rapid RH® Digital pH Meter

Rapid RH Digital pH Meter
The digital pH meter is a valuable accessory to the Rapid RH moisture measurement system. The pH meter is designed for precision and convenience, and Wagner Meters recommends utilizing its pH test kit as an integral part of Rapid RH moisture assessment.

Rapid RH pH MeterSlab moisture condition and pH are interrelated but measured separately. Generally speaking, the pH will be higher when the RH in the concrete is higher. High pH, as we’ve seen, just like high moisture levels, can make the concrete slab ill-suited for a proper flooring installation.

For this reason, it’s strongly advised that flooring installers and contractors obtain a conclusive assessment of both factors in order to give the “okay” to go ahead with a job. Of course, this goes without saying where both measurements are required.

Research has proven the in situ RH assessment method to be the most accurate method for determining the RH of a concrete slab. And achieving the appropriate RH level will also help ensure the appropriate pH level for a safe, long-lasting flooring installation.

Last updated on August 31st, 2021