Screed Moisture Meter
A screed moisture meter is a small and reliable measuring device for determining the present moisture in, for example, screed, concrete and wood. The corresponding scales for the moisture measurement are already stored in the library of the measuring device. After selecting the scale, the required measurement can be carried out with the moisture meter. Just after a few seconds, the measurement result is displayed on the screed moisture meter both numerically and graphically.
A separate alarm limit can be stored for each scale on the moisture measuring device. As soon as the set alarm limit is exceeded, an acoustic alarm in the screed moisture meter is triggered. In order to protect the inserted batteries, the tester switches off after 5 minutes of no-operation.
Another special feature of the measuring device is the possibility of displaying the calcium carbide method (CM% / CM method) for screed. Also, for this measurement, the moisture measuring device is placed on the surface to be tested. Using the corresponding scale, the measured value is converted into a CM% value (calcium carbide method). Thus, by means of the calcium carbide method the guideline value for the specialist for floors is obtained.
Calcium Carbide Method (CM method) for Screed Residual Moisture Measurement
It goes about a well-known method for indirect moisture measurement. Here, the carbide method is subject to clearly erroneous influencing factors. Since the local practitioner has been used to this method of moisture measurement for decades, it still plays a role, even though decreasing, e.g. when assessing the adhesiveness of the floor coverings on the screed. According to this method, calcium carbide reacts with water to calcium hydroxide and acetylene. The water comes from the previously obtained sample material (10 ... 50 g), which is crushed in the reaction vessel by the also present there steel balls, in the result of a 10-minute shaking and the moisture present in the container reacts with the calcium carbide. The gaseous acetylene causes a pressure rise that is measurable and can be correlated directly to the moisture content. The reaction containers made of stainless steel and with the display of the container pressure via a pressure gauge, are applied for this purpose. The maturity of a screed can thus be determined indirectly but with sufficient accuracy with the help of the CM method.
Advantages of the CM Method / Disadvantages of the CM Method
The advantages of the CM method for moisture measurement in the screed are quick feasibility of the test on site (in contrast to the time-consuming drying test), the sufficient accuracy and the court usability of the results in the event of a dispute.
Due to the strongly changed cement-screed mixtures (significantly changed water contents / moisture contents) in modern building construction, the meaningfulness of the CM method can no longer be assessed as very selective and the limit value of 2% moisture in the concrete-screed, previously used for moisture evaluation can lead to wrong decisions when assessing the suitability for covering.