Testing moisture content

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.

Recording readings

  • Note especially the highest readings found.
  • Note the areas, their boundaries and shapes, of the highest readings.
  • Note any nearby suspect sources.

Percentage readings

  • 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.

Interpreting readings

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:
    1. Drywall:    45-70% mid (max 100%)
    2. Masonry:   45-70% mid (max 100%)
    3. Softwood:  16-18% mid (max 53%)
    4. Hardwood:  15-17% mid (max 35%)

Reporting results

  • Decide if moisture source is condensation or a leak.
  • Decide if a leak is continuing or not.

Further analysis

  • Use an infrared thermometer or camera to look for cooler (possibly damper) locations.

©Richard Knights, Blue Sky Inspections, Seattle, http://www.inyourair.com