Moisture Testing in Concrete Floor Slabs

Concrete floors and screeds should be dry enough to allow resilient floor coverings to be installed without follow-on moisture-related damage.

If moisture is present in a concrete floor slab or screed it can:

1. Cause damage to the floor covering material
2. Affect certain flooring adhesives
3. Cause bubbling, blistering or delamination of the floor coverings
4. Affect certain types of levelling compounds or underlay materials
5. Damage certain screed materials
6. Affect or damage wall or skirting materials or finishes.

The drying out of a concrete floor slab (moisture leaving the slab over time) is typically a slow process and a common method for assessing the floor condition is using in-situ relative humidity probes.

Infrastruct use the Tramexhygro-i₂probes for in-situ relative humidity monitoring of concrete floor slabs and screeds.

ASTM Standard F2170-19a ‘Standard Test Method for Determining the Relative Humidity in Concrete Floor Slabs Using in-situ Probes’ describes the quantitative determination of the percent relative humidity in concrete slabs.

A summary of the procedure to measure relative humidity in concrete floor slabs is as follows:

1. In hardened concrete floors or screeds, drill a hole with a specific diameter in the floor to a predetermined depth and clean out using a hole brush and vacuum system. Avoid embedded reinforcement, if present, in the slab. See Figure 1 showing rotary drilling in a concrete slab with a dust removal system prior to inserting the plastic sleeve.
2. Push a plastic sleeve, of suitable length, into the drilled hole and cap off and seal. The plastic sleeve allows measurement of the relative humidity of the concrete at a specific depth.
3. Install the relative humidity probe into the hole and recap as shown in Figure 2.
4. The Standard F2170-19a recommends a defined number of RH% probes per square meter in the floor slab and requires certain test locations to gather as much information on the moisture distribution in the floor.
5. Allow at least 24 hours for the RH% probes to achieve moisture equilibrium within the sleeve before making the relative humidity measurement. We measure relative humidity in concrete and screeds using the Tramex CMExpertII system as shown in Figure 3.
6. Record the result carefully ensuring the reading does not drift by >1% and the probe is in temperature equilibrium with the floor.

Non-Destructive Moisture Measurement

To scan concrete floors for changes in the moisture content, the Infrastruct Team also uses the Tramex CMExpertIIdigital meter (Impedance Mode). In this mode, the meter measures the surface moisture using the electrical impedance principle.

Measurements are non-destructive and large areas can be scanned quickly. See Figure 4 showing the Tramex CMExpertIIdigital meter in operation on a floor slab.