Testing moisture in materials
Test for damp materials containing excess moisture using portable continuous direct-reading survey meters , which are of 2 types:
- a pad-type (pinless) meter that sends radio waves through the material:
- regular shallow (an inch) meter to check just under the surface (the General/Mannix Moisture Hunter or the Tramex/Dri-Eaz Moisture Counter), or
- deep (several inches) “wet-wall” meter to check across insulation or a wall cavity (the Tramex Wet Wall Detector), and/or
- a pin-type meter that pokes needles into the material (the Lignomat MiniLigno) either
- for surfaces (millimeters), or
- for underlayers (inches deep) using a slide hammer.
- (Deep testing is used for EIFS siding.)
Taking moisture readings
- Adjust a pad meter sensitivity for drywall, masonry, softwood, or hardwood.
- Put your hand on the pad, to confirm it goes to 100%.
- Test a dry area to get a control baseline for the material.
- Test where you expect the most dampness (is it a high reading?).
- Scan to find the extent of dampness (like floor to ceiling?).
- Scan to follow any tracks to the source of moisture (like window vs. plumbing?).
- Mark the outline of dampness with a pencil (triangle?).
- Test also using a pin-meter to verify suspicious high readings.
- Ignore isolated spots the might be nail heads, and strips like metal corner bead.
- Note especially the highest readings found.
- Note the areas, their boundaries and shapes, of the highest readings.
- Note any nearby suspect sources.
- The pattern of moisture is often more useful for diagnosis than the numbers.
- Mold needs a moisture content (MC) of at least 20% to survive on wood.
- A certain percentage dryness might be required, such as <19% before enclosing framing, <18% before installing insulation, or even lower for wood flooring.
The meters show percentage moisture content (the analog Tramex/Dri-Eaz with only a dial).
- Levels in the lowest scale indicate normal dry materials, mid-scale indicate slightly damp materials (15-18% for wood), and above two-thirds of full scale indicate damp materials and the meter starts beeping.
- The digital meter by General/Mannix also shows indicator lights (where green are dry, yellow mid-scale, or red damp) for 4 different materials:
- Drywall: 45-70% mid (max 100%)
- Masonry: 45-70% mid (max 100%)
- Softwood: 16-18% mid (max 53%)
- Hardwood: 15-17% mid (max 35%)
- Decide if moisture source is condensation or a leak.
- Decide if a leak is continuing or not.
- Use an infrared thermometer or camera to look for cooler (possibly damper) locations.
©Richard Knights, Blue Sky Inspections, Seattle, http://www.inyourair.com