Moisture Meter Errors
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Moisture meter errors: this article lists the common sources of errors (including simple mistakes in application) when using a moisture meter to measure building materials or to screen a building for hidden leaks, water, or moisture.
This article series explains the use and reliability of different types of moisture detection equipment to find water entry problems on buildings. We demonstrate where moisture meters work successfully and where (and why) they don't.
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Common Sources of Error When Using a Moisture Meter
In addition to the more subtle moisture measuring errors and troubles discussed in MOISTURE METER STUDY, we list here some typical sources of moisture meter error, adapted from the owners manual for the Tramex Compact Moisture Meter for Wood.
Photo at left, the Tramex Compact Moisture Meter.
- Calibration: failure to perform a calibration check and battery check before using the instrument
- Contaminants in the material being measured: anything that changes the electrical conductivity of the material from its original state can affect a moisture measurement that depends on electrical resistance (all pin type meters and at least some electronic moisture meters).
Examples are salts deposited in the material from a long history of water passage or leaks, wood preservatives or pesticides or other treatments. - Distance: as our study above demonstrates, if scanning building cavities for leaks and moisture, the cavity or insulation may be quite wet but too distant from the sensor to provide a reading.
- Paints & coatings: a pin type and some electronic type sensors may be affected by conductive paints or coatings on the surface being measured
- Presence of other materials: a moisture sensor may be detecting metal from foil faced building insulation, metal lath, water pipes, electrical wiring, etc.
- Time since the water leak or wetting event: when testing a material or building cavity for leaks or moisture, a prior leak, even severe flooding bad enough to have produced significant hidden mold contamination, will not show up as moisture at all if the cavity and its contents are dry at the time of testing. When measuring moisture to decide if painting is advisable this is not necessarily an issue.
When measuring moisture as a "mold scan" or to look for hidden rot, insect damage, or a history of building leaks and damage, this is a key limitation in moisture meter use.
Therefore, relying only on moisture meter readings to estimate building leaks, building leak history, and hidden water-related damage, without also performing an expert visual inspection of the building exterior and interior, and without taking note of the building's leak history, would be an unreliable approach.
At MOISTURE METER STUDY we explain this key factor in erroneous use of moisture meters in buildings. - Scale: choose a moisture meter designed for measuring the type of material being tested; for a moisture meter with multiple scales, be sure to select the appropriate scale, e.g. Concrete, Plaster, Wood.
- Surface moisture: the moisture meter may be misled by unimportant surface moisture on the material being tested, confusing surface moisture for actual moisture within the material.
- Temperature: moisture meter readings of some materials, including wood, are impacted by the temperature of the material being tested. Typically the moisture meter is calibrated for 20C or 60F. Higher temperatures produce higher moisture "readings". The manufacturer of your moisture meter may provide a temperature correction table to adjust the reading for accuracy when appropriate.
For example, for the Tramex Compact Moisture Meter (photo at above left), depending on temperature, the moisture content percentage reading may need to be adjusted by a figure ranging from -12 to + 15 %.
- Wood species: when measuring moisture content in wood, variations in wood density and species-related composition affect the wood's electrical resistance and thus the moisture reading obtained. Even the same wood species but from different places of origin may behave differently. A moisture meter manufacturer of an instrument intended for accurate moisture measurement in wood may provide an adjustment table. Wood species are collected into groups by species properties and a moisture meter correction figure will be provided for each group.
For example, for the Tramex Compact Moisture Meter (photo at above left), six wood species groups are defined and moisture adjustments for wood species by group range in percent (on the meter moisture content scale) from about 0.3% to 3%.
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Continue reading at MOISTURE METER CHOICES or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
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Citations & References
In addition to any citations in the article above, a full list is available on request.
- Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor [Website: /www.house-whisperer.com ] is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-873-8534 or by Email: johncranor@verizon.net
- BASEMENT MOISTURE CONTROL [PDF] U.S. Department of Energy
- Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
- Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724 ISBN-13: 978-0471331728
- Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
- CRAWL SPACE MOISTURE CONTROL [PDF] U.S. Department of Energy
- Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
- Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting:
A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level. - Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
- LOG HOMES: MINIMIZING AIR LEAKAGE [PDF] U.S. Department of Energy
- Masonry, Engineered: Using the Canadian Code, J. I. Gainville, Cantext publications (1983), ASIN: B0007C37PG
- Masonry, Non-reinforced masonry design tables, Hans J. Schultz, National Concrete Producers Association and the Canadian Masonry Contractors Association (1976), ASIN: B0007C2LQM
- MOISTURE CONTROL in BUILDINGS [PDF] U.S. Department of Energy
- MOISTURE CONTROL in WALLS [PDF] U.S. Department of Energy
- Slab on Grade Foundation Moisture and Air Leakage, U.S. Department of Energy
- VAPOR BARRIERS or VAPOR DIFFUSION RETARDERS [PDF] U.S. DOE - how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
- VENTILATION for ENERGY-EFFICIENT BUILDINGS [PDF] Purpose of ventilation, ventilateion strategies, etc.
- In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
CONTINUE READING or RECOMMENDED ARTICLES.
- Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The HOME REFERENCE BOOK - the Encyclopedia of Homes and to use illustrations from The ILLUSTRATED HOME .
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.
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