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Moisture Meters

Moisture Meters

UNDERSTANDING MOISTURE CONTENT

Moisture content, expressed in % MC, is a measurement of the amount (in terms of weight) of water present in the material compared to the bone dry weight of the material.

MOISTURE IN WOOD

Wood is a hygroscopic material. It will absorb or release moisture until it reaches equilibrium with its surroundings. Scientifically speaking this means that when vapour pressure of the wood surface moisture equals the vapor pressure of the moisture in the air, we say that they are in equilibrium. This moisture content of the wood surface is known as Equilibrium Moisture Content.
An EMC table of several locations in different calendar months of the year is shown above for better understanding of the above discussion:

Take for example, if a solid timber door made in Indonesia is sold to Sydney, Australia in Jun. The EMC there in June is reported to be 13%. If the timber door is dried to 9% , the timber will start to absorb moisture starting from the surface until it attains 12 or 13% MC on the outside, over a period of time. The core MC will probably be increased from 9% to 11%. There will be some expansion of the door due to moisture absorption and the customer will have problem closing the door.

If the door was not dried properly and the MC was at 16%, at EMC of 13% , the wood will give up moisture until the wood surface reached 13% MC. In this case, the wood will contract, and the door will develop cracks at the joints.

This is the reason why all timber products must be dried to relevant MC with respect to the local EMC conditions.The use of a good moisture meter is important.

Type of Moisture Meters

1.) PIN TYPE WOOD MOISTURE METER

Pin-type moisture meters use the principle of electrical resistance to measure the amount of moisture in the wood in terms of percentage of the wood bone dry weight. When activated, electrical current travels down one electrode, through the material being tested, and into another electrode.The amount of resistance to the current is used to calculate how much water is present in the material. Since water is a conductor, the less resistance there is, the higher the moisture content of the material being tested. For accurate wood moisture readings, always use MC meters with wood specie selection and temperature compensation. Temperature affects the MC measurement. Different wood has different resins and minerals absorbed, research done in Forestry research centres have the wood classified into groups in terms of their electrical conductivity. 

The most accurate method of determining wood moisture is by the oven test method based on ASTM 4442 Standard.

It is also important to know that a wood product has a tolerance of EMC of + 2%. This is what we call Moisture Absorption or Desorption Hysteresis. If a piece of wood has a MC of say 10%. The wood moisture will stay at 10% in an EMC environment of between 8% to 12%. It is equally important to note that MC measurements exceeding 60% will not be accurate as the resistance will drop significantly after 60%. Moisture Content of more than 60% is of no importance to anyone.

Pin type meters will have pinpoint accuracy if insulated electrodes are used. Only the tips are exposed. Even if there is surface water, the insulated shanks of the electrode will not be connected to each other to give wrong readings.

2.) PINLESS TYPE WOOD MOISTURE METER

Pinless meters will be very accurate if the moisture distribution across the depth is uniform. For a thick piece of wood, chances are that the wood moisture has not been completely equalized and core moisture is still high. In this case, the pinless meter will read the average value. For timber of 25mm and below, the moisture across the timber is uniform, and the pinless meter will give very accurate readings. For thicker timber more than 40mm, the moisture between the surface and the core are likely to be different. Only if the thick timber is given enough time to equalize, there will be a moisture gradient across the depth.

Pinless meters use a non-penetrating sensor that scans the wood and does not leave damaging pinholes on the wood’s surface. This makes the use pinless moisture meters perfect for finished products inspection.

There are 2 types of pinless meters.

The 1st type measures the capacitance or the di-electric strength of the wooden material. The presence of moisture affects the di-electric strength. The timber density and thickness can also affect the di-electric strength or capacitance measurement. Such meters are cheap but highly inaccurate.

The 2nd type uses electromagnetic (EMF) signals to measure the MC. An electrical waves will be sent out at a certain frequency and to a certain penetration depth. This creates an electromagnetic field right underneath the sensor pad. The sensor detects the return waves which are affected by the amount of moisture present in the wood. The wood material density and thickness also affect the readings.

Good quality non-destructive or pinless moisture meters have compensation for density and selection of thickness. If no thickness selection is available, the manufacturer will clearly state the allowable thickness for accurate MC readings.

A piece of timber with a rough surface will affect the accuracy of the measurement. There will be small air gaps below the scanner face that affect the accuracy. Pinless meters have a fixed scanning depth. If a piece of wood is too thick, the meter will not be able to take a reading of the deepest layer of the wood. If the wood is too thin, the waves may penetrate material and read any material behind the wood. 

WAGNER latest range of Orion 930, 940 and 950 meters have 2 selectable depths of measurement – ¼” and ¾”.

NIGOS DVD241 pinless wood moisture meter has selectable wood thickness from 2mm to 19mm (in increments of 1 mm)  and 1 thickness setting for wood from 20mm to 40mm. The wood density is also selectable from 200 to 1100 kg/m3.

The NIGOS DVD241 is a very convenient meter to have. Instead of having multiple meters for different timber thickness, this one single meter will allow measurements of timber products with different thickness and densities.

A rubber bumper is provided to give goood protection from mechsnical damage. The meter is very easy to use and very reliable. This high quality moisture meter comes with a 3-years warranty against manufacturing defects. 

3.) CONCRETE MOISTURE METER

When laying wood flooring and other floor coverings on concrete floors, it is important for the concrete be dried to the right moisture content (4% to 6%, depending on geographical region) with respect to the EMC of the region. The moisture evaporating from the concrete will be absorbed by the wood flooring directly causing it to expand and bulge out. 

Tramex is the leading manufacturer of Concrete meters from Ireland, their concrete meters analyse the moisture conditions of the top 3/4” of a concrete slab, giving instant and quantitative readings of the percentage of Moisture Content by weight. 

 

The Tramex Concrete Moisture Encounter X5 - CMEX5 is an instant, precise, digital, non-destructive moisture meter for measuring quantitative moisture content % in concrete floors and slabs using Gravimetric testing as a baseline. The CMEX5 also provides Carbide Method equivalent readings for concrete and other cementitious substrates as well as comparative readings for Gypsum and as per ASTM F2659. The CMEX5 features a built-in ambient RH sensor that measures Ambient Relative Humidity, Temperature, Dew Point, and Humidity Ratio (or Mixing Ratio) of the environment. A bayonet plug-in port allows for optional wood pin probes or Tramex Hygro-i2 Relative Humidity Probes. Bluetooth connectivity to the Tramex Meters App allows for visualization of readings and data reporting to mobile devices, to GeoTag test results, create, save and share photos, reports and charts.

The use of the CMEX5 can be extended with the optional Concrete Moisture Probe which detects in-situ quantitative moisture content within the concrete to an extendable depth of up to 4" (100mm)
This complete concrete testing system provides the most comprehensive information available for any flooring professional to both identify and eliminate moisture issues, as well as comply with international standards for the floor covering industry.

Moisture Meters Logos  DELMHORST                           GANN                              LOGICA                            MERLIN                               NIGOS                       TRAMEX                     WAGNER

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