LIMIT | Everything can be measured 1
ABOUT MOISTURE Relative humidity (RH) The air’s a
bility to absorb water varies with the temperature. The higher the temperature, the more water the air can absorb. To express the amount of moisture in the air, we specify the relative humidity in the unit % RH. Dew point The dew point is expressed in °C and specifies the temperature at which humidity reaches 100% RH and water vapour (condensation) is formed. Moisture in materials Moisture content (% FC) is the difference in percent between the weight of the water in moist material and the weight of the dried material. The moisture content can be determined by weighing-drying-weighing. In wood, the moisture content can also be measured using an electronic moisture content meter, as the electrical properties vary with the moisture content. In concrete, moisture content can be measured by drilling a hole, vacuuming it clean, sealing it and allowing it to stand for several days until there is equilibrium (see moisture balance). You can then measure the relative humidity in the drill hole, which in turn will provide the moisture content in the concrete when you know the absorption curve for that particular concrete. It is important to vacuum thoroughly, seal tightly around the moisture sensor and allow it to stand in the drill hole until there is equilibrium. The drill hole should rest for approx. 48 hours before taking the measurement in order to obtain a correctly balanced moisture content. Wait at least half an hour after inserting the probe in the hole before reading the measurement. Choosing a moisture meter You should ask yourself the following questions before choosing a moisture meter. • Which material should I take a measurement from? • How far into the material do I need to measure? • Which structure should I measure from? • What accuracy and what moisture level will I need to measure? • Find out the paint manufacturer’s recommendations for maximum moisture content prior to surface treatment. 130 |