Moisture Meters- The Key Facts
The measurement and detection of moisture and the meters used is a complex and important topic that is frequently misunderstood.
This article will outline the differences between the concepts ofÂ â€˜moisture measurementâ€™ and â€˜moisture detectionâ€™ as well as explain the most appropriate type of meter to use in different situations.
Moisture Measurement In Timber
The most common material in which moisture content can be â€˜measuredâ€™ by using a moisture meter is timber. The typical tool used for this purpose is the widely available pin type meter (also known as an electrical resistance/conductance and destructive meter).
These instruments work by reading across the two pins and detecting the change in resistance when they come into contact with the timber.Pin meters will give a pretty good indication of the moisture content of timber. They are made and calibrated to do this on particular species of timber for example, Douglas Fir. These instruments work because the conductivity of timber (also known as the density), is reasonably constant throughout different timber types and is proportional to the moisture content. As there are timbers which have different densities to that which the instrument has been calibrated to, most meters are supplied with a set of tables which give the adjustments which need to be made dependant upon the type of timber being tested.
Limitations Of Pin Meters For Building Surveys
As described above, the common pin meter has been designed for use on timber and not any other materials. This fact is often not appreciated by many users who rely on pin meters to â€˜measureâ€™ moisture content in other materials such as masonry, plaster or wallpaper. This is not actually possible as there are major variations in, for example masonry and therefore no consistency between any two samples from different sites. The same holds for most common building materials.
All a pin type meter can indicate, at best, is whether moisture may be present but they can not measure the actual level of moisture in the material. The danger of using a pin meter is that the instrument only reads across the very small area between the pins. This is not such a problem with timber due to the homogenous nature of it. However, when looking for moisture in an internal wall, it would be necessary to make many pin holes all over the wall in order to get a thorough indication of whether there is a presence of moisture. This is time consuming and leaves behind unsightly holes. When faced with tiled areas (such as kitchens & bathrooms) the pin meter can not be pushed through tiles and as a result no readings can be taken or at best only a surface reading is obtained. The presence of certain substances on the surface of the material being tested, such as condensation and salts, will also affect the readings.
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