The term “Moisture is often confused with “humidity”. Humidity or better relative humidity is defined as “the ratio of the partial pressure of water vapor in the mixture to the saturated vapor pressure of water at a prescribed temperature.”
Products to define humidity and other climatic parameters are presented in our section Climatic Conditions. Moisture refers to the presence of a liquid, especially water, often in trace amounts. The moisture content of materials to be coated is an important parameter. Fresh concrete for example has a very high moisture content. The moisture evaporates through the surface of that concrete. If the surface is closed off with a non-permeable coating layer the moisture is trapped and will cause damage to the coating over time. The same goes for timber which is not kiln- or air dried. Coating of moist materials often leads to adhesion failures. The moisture of a substrate is not just critical for coatings also (wooden) flooring, wall paper or other materials that cover a substrate will demand a certain moisture content of that substrate. Further moisture can be found in powder or grain-like materials such a cereals, pigments, powder coatings etc..
There are various systems to define the moisture content of a material.
Electrical conductivity / resistance and impedance
These instruments measure the resistance of an electrical signal between points at the material to be measured. Various techniques are being used to enhance accuracy. There a simple instruments that just provide an indication of the moisture content but also sophisticated gauge that provide accurate readings. This kind of meters are often used to measure in solid materials like timber, concrete, masonry etc..
Reagent pressure test or carbide test
This system is based upon a chemical reaction of water with carbide. A defined quantity of material to be measured and carbide is placed in a special closed container and then mixed. The reaction of the water in the material and the carbide creates a pressure which can be read on the pressure gauge which is integrated in the container. There is a direct ration between the pressure and the water content. This type of test are not so easy to perform but the results are very accurate. Often these test are done on concrete or stone.
Gravimetric or moisture balance
This method is based upon the loss of weight of a material after it is dried. A special analytic balance is used to measure the total weight of the sample. Than the sample is dried with a special device which is integrated in the balance. The evaporation of the moisture will reduce the weight of the sample. When the weight of the sample remains stable it indicates all moisture has been taken out of the material and the drying process stops. The difference between “wet” and “dry” sample is an accurate indication of the moisture content. This type of test is mainly used for grain- shaped materials or powders.
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