Electrical moisture meters

When you have a dampness (excess water) problem the first stage is to get an understanding of the excess/or free water. The electrical moisture meters will help with this.

protimeter survey master electrical moisture meter

Electrical meters were specifically designed for moisture readings in timber. They provide factual measurements in terms of % Wood Moisture Equivalent. Typically, the default timber calibration is based on pine in the UK.

The two main types of electrical moisture meters are:

Filr MR77  combined conductivity, capacitance and relative humidity meter
moisture meter

The conductivity meter uses two pins and the meter measures the conductivity between the pins on the surface to be tested, this gives wood moisture content % in timber which is quantitative.

Tramex ME5 electrical moisture meter

capacitance/impedance meters use radio waves to measure depths of 10-19mm below the surface. This method, often referred to as ‘search mode,’ enables rapid assessments. However, its range calibration can be misleading, making it unsuitable for standalone moisture diagnosis.

 Timber %WMERelative Readings
Protimeter Surveymaster5% to 99%70 to 999
Flir MR770% to 99%0 to 100
Tramex ME55% to 30%0 to 100
The operating range of some of the electrical moisture meters that are available

In most building materials, pin readings are relative and do not directly measure moisture content. Instead, visual damage and patterns of meter readings help us understand dampness issues. Pre-purchase surveys often rely on qualitative results, especially when owners prefer to avoid pinholes caused by capacitance meters. Inaccurate search or scan modes may lead to misdiagnosis. Combining both methods provides a comprehensive assessment of dampness.

building salts affecting a electrical moisture meter

Salts present in the building structure can lead to elevated readings on an electrical moisture meter. These salts enhance the material’s electrical conductivity, even when there is no excess moisture. Such readings suggest a potential historical issue.

A comprehensive report should specify the type of moisture meter employed and the methodology used. While an educated eye can discern patterns of damage caused by dampness, an electrical moisture meter can provide valuable assistance. However, when dealing with masonry, results obtained solely from scan mode should be approached with caution. It is advisable to engage a qualified professional for thorough inspections.

Possible dampnessSKB2505007501000125015001750
Ineffective damp-proof course>25%95909085*1000
Plaster bridging or condensation behind skirting>20%75000000
Sample of Patterns of surface relative meter readings. *Salt band. Note: Scan mode should never be used for this work

Depth of moisture meter pins

protimeter pins for measuring moisture in timber
measuring pins

The pins of the meter must only be inserted 2-3mm into the surface to be measured for a calibrated result on the digital or analogue display.  By pushing the meter pins deeper, you will get a higher reading but this is an error in relation the meters calibration in moisture in timber (WME).  When taking readings on timber the pins must be inserted parallel to the grain to get a correct moisture reading.

Using Deep hammer probes

deep hammer probes take moisture reading within large timbers
Deep hammer probes

The pins in a meter give a reading of the surface of the timber, which is ok in small dimension timber. To understand what is happening in larger timbers i.e. large joists and beams, using a deep hammer probe give the moisture reading deeper inside, and this can guide any remedial measures by comparing the surface reading, with the reading at depth.

One method of assessing at timber floor is to find the joist below the floorboard, then take a surface reading, then using the hammer probe take moisture readings at different depths.

Deep probes into masonry

Deep masonry probes allow relative reading within a wall.
deep masonry probes

By drilling two 5mm holes 20 to 40mm apart into the masonry you can insert the probes which will then give a relative reading at depths and will help in diagnosing the form of dampness.

Calibration of the electrical moisture meter

For a conductivity meter there is a testing wire which you place on the pins and will confirm is the devices is working correctly.

For the scan mode thigs are not as simple.  For your Protimeter Surveymaster you select a suitable wall in your office and take a reference reading if this changes recalibration may be necessary. For instance, the Flir MR77 has a built-in recalibration function.

The manufactures handbook for you meter should advise the best method of calibration and meter settings for different types of timber

Property Care Association
Training available at https://www.property-care.org/
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