Drywall moisture readings over 0.5% Moisture Content should be considered higher than generally acceptable and require further drying or investigation and mitigation.
Drywall needs to be as dry as possible since moisture can negatively affect its structural integrity and may cause microbial growth.
Moisture readings in drywall can be taken with a drywall moisture meter that is specifically calibrated to measure the moisture content percentage (%MC) in drywall or by using the reference scale on a comparative moisture meter.
Drywall moisture content
To measure drywall moisture content accurately, a moisture meter must be specifically calibrated for this purpose. The Moisture Encounter MEX5 features two scales designed for drywall readings.
In the pinless, non-destructive mode, the Drywall scale sensitivity is appropriate to the density of the material, allowing for meaningful comparative readings on a 0-100 scale. The Moisture Encounter MEX5 also incorporates dual depth capability for comparative drywall readings. Regular depth reads up to 30mm (1 ¼”) and the shallow depth reads to 9mm (⅜”). The shallow depth scale will greatly reduce or eliminate the influence of the substrate behind the drywall.
In pin-probe mode the drywall scale is calibrated to give actual moisture content %MC measurements in drywall, in alignment with the ASTM C1789 standard. This pin-mode Drywall %MC scale provides measurements ranging from 0.0 to 8.5% MC. The Moisture Encounter MEX5 features ‘traffic light’ LED indicators to show what is generally accepted as a good indicator of low/medium/high readings. The breakdown for these low/medium/high measurements in %MC in drywall is as follows: Green 0 - 0.5 / Yellow 0.6 - 0.7 / Red 0.8 - 8.5.
Drywall moisture levels
Moisture levels can also be evaluated on a comparative scale, also called a reference scale. A pinless moisture meter such as the Moisture Encounter MEX5 or ME5 will detect elevated moisture levels in drywall. Initially, a reading is taken in a known dry location, serving as the 'acceptably dry' reading, or baseline level. Any readings higher than this baseline may indicate elevated moisture levels.
The benefit of pinless moisture meters for drywall is that they can cover large surface areas quickly without damaging the material under test. Areas with readings higher than the baseline can be investigated further with the pin probe for actual drywall moisture content measurements.
Both Moisture Encounter ME5 and MEX5 moisture meters feature shallow depth scales which allows the user to compare moisture levels without any influence from the substrate or airspace behind the drywall. As the shallow depth scale takes readings from a small sample footprint area and depth, these readings are comparable to the precision of pin-probe readings.
It is still recommended to confirm any suspected high-moisture areas with the Moisture Encounter MEX5 pin probe for drywall % moisture content measurements.
High moisture readings in drywall
When a moisture meter indicates high moisture levels in drywall, further drying or investigation and mitigation is recommended. High moisture in drywall can cause structural damage and may promote microbial or mold growth.
A good tip to note is that high readings can be false positives if a pinless moisture meter detects conductive materials, such as metal or wiring, behind the drywall surface.