Get reliable results when measuring moisture in concrete

Published 2026-09-30

Measuring the moisture level in concrete is important in several different contexts, both in new construction and in existing buildings. This may involve checking that the concrete is sufficiently dry before applying a new surface layer, investigating conditions in cases of suspected moisture problems, or monitoring how moisture levels change over time.

At the same time, moisture measurement in concrete is not always as simple as placing a probe and reading a value. How the measurement is performed, the measurement depth used, and the conditions prevailing at the time of measurement can all affect the result.

Why measure moisture in concrete?

After casting, the moisture needs to be able to dry out, but the speed at which this happens depends, among other things, on the composition of the concrete, the thickness of the structure, and whether the concrete can dry in one or more directions. If a moisture-sensitive material is installed before the concrete is sufficiently dry, it can have consequences for the finished structure. Therefore, the moisture level needs to be assessed before deciding whether the work should proceed to the next stage in the construction process.

Even in older structures, there may be reason to check moisture conditions, for example during renovation, changes in building use, or when moisture damage is suspected.

What affects the measurement result?

Placement of measurement points
Moisture conditions in a concrete structure are not necessarily the same everywhere, which makes the placement of measurement points important. The placement and number of measurement points need to be adapted to the structure and the purpose of the measurement. When measuring according to the RBK method, there are guidelines for the placement of measurement points.

Choose the correct measurement depth
The relevant measurement depth depends, among other things, on whether the structure dries from one or two sides.

Prepare the measurement hole
Drill cuttings and dust must be carefully removed, and the measurement tube must be installed so that the measurement is sealed. Details such as the placement of the O-ring and ensuring the probe is clean are also important. Dirt, drill cuttings, or a faulty seal can affect the measurement result.

Monitor the temperature
Temperature changes can affect moisture conditions and thus the measurement. Therefore, ensure that the ambient temperature is stable. The probe should also not be colder than the concrete when it is installed, as condensation on the probe can affect the measurement.

Wait until the measurement value has stabilized
After installation, the probe needs time to reach equilibrium with the air in the measurement hole. For RBK measurements, readings should be taken no earlier than 12 hours for concrete with w/c ratio ≥ 0.4 and after 48 hours for concrete with w/c ratio < 0.4.

Document the measurement
To be able to assess and follow the measurement results, the measurement must be documented. In addition to the RH value itself, it is relevant to note, for example, temperature, date, time, and measurement point. Documentation makes it easier to compare measurements over time and provides a basis for deciding on the next step in the construction process.