In order to investigate and establish whether a material or a space contains moisture there are various indicators and measuring instruments available. One can roughly divide the measurement objects into four main groups;
- Air (moisture in surroundings)
- Brick/Leca/Siporex or other porous stone material
We have chosen to focus on measuring in concrete that can be somewhat different compared to other materials. The best way to get a reliable result is to measure relative humidity in the pore system of the concrete.
WHAT EQUIPMENT SHOULD I USE?
RH Meters are usually used for measuring in concrete. Holes are drilled in the concrete of a suitable diameter and depth, after which the probe (sensor body) is inserted and after a time registers the relative humidity of the material.
It is important that the instrument is properly calibrated to obtain accurate readings.
HOW TO DO THE MEASUREMENT
The drill holes must be clean from dust, which can be hygroscopic, i.e. adsorb moisture resulting in inaccurate readings. Furthermore the probe’s temperature must not fall below that of the concrete because this can mean that moisture condenses on the sensory body. Therefore wait until the probe has acclimatised.
To get an assured value, measurement should first be taken between 1-3 days after drilling.
WORTH THINKING ABOUT WHEN MEASURING RH-% IN CONCRETE
- Drill to the correct depth. 20 % of the concrete slab thickness if drying can occur from both above and below and 40% of the concrete slab thickness if drying can only occur from one direction.
- Vacuum the hole carefully after drilling!
- Install the measurement tube and seal with sealing compound between the concrete and the measuring tube. Cut the measuring tube to the correct length of necessary. The measuring tube is then plugged.
- Wait at least 3 days after drilling before taking the final measurement.
- Ensure that the measuring probe is not a lower temperature than the concrete in order to avoid condensing on the measurement probe. To avoid this you can hold the probe in the process air for the machine for a moment.
- Allow the probe to sit in the measurement hole until there is no change in the temperature or RH%. At least 30 minutes.
- The measuring probe can be left in the hole between measurements.
This is a general guide. You need to consider the environment and type of concrete you are working with.
In order to get started with a drying process sooner, one can take an indicating measurement in conjunction with drilling the measurement holes. In this way one can gain valuable time.
The concrete around the hole heats up slightly when one drills so that approx. 8-10% units too high a value for the RH is obtained. See example below:
A plastic mat must be laid, the adhesive can tolerate max 90% RH. You take an indicating reading after drilling and will decide about further actions.
- Read off value: <95% RH
-Dry. Wait 3 days and measure again.
- Read off value: >95% RH
-Probable moisture, start drying and measure again after three days.
- Read off value: =100% RH
-Guaranteed moisture, start drying!
Always maintain a good margin with the estimated measurement value and wait for at least 3 days before final measurement.
DO YOU WANT TO LEARN MORE ABOUT MEASURING IN VARIOUS MATERIALS?
In our own building laboratories, theory and practice are combined; water damage in different structures is dried and evaluated with measurements. Read more »