Issue link: https://hi.iaq.net/i/248503
www.epa.gov/iaq/moisture Appendix C – Testing Moisture During Construction The moisture content of wood, wood products and other porous materials is an important factor in mold growth and other moisture-related problems. A porous material susceptible to mold growth, such as wood, oriented strand board (OSB), medium density fiberboard (MDF) or untreated paper-faced gypsum board, will experience mold growth if its moisture content is too high. Damp porous materials that are resistant to mold growth, such as concrete products and treated lumber, may indirectly support mold growth by wetting vulnerable materials that are in contact with them. For example, untreated paperfaced gypsum board attached to damp lumber or concrete may be the site of mold growth until the damp materials dry. by weighing the test sample while damp, drying the sample using heat or desiccant salts, and then reweighing the sample. Electronic meters with direct reading scales or displays have been developed for wooden materials. Their use on lumber is extensively documented. ASTM D 4444-92 (Reapproved 2003) Standard Test Methods for Use and Calibration of Hand-Held Moisture Meters describes several types of moisture meters, their use on wooden materials, and quality assurance/quality control (QA/QC) procedures. Knowing the moisture content of porous building materials other than wood or wood products, such as gypsum board and concrete slabs or concrete masonry units, is also important. Some electronic moisture meters have calibrated scales for materials other than wood, for example concrete, brick and plaster. It has become common practice in the building diagnostic field to test materials other than lumber using electronic meters and to report the results using the scale for lumber. In this way, investigators report the moisture content of gypsum board, MDF and OSB as the wood moisture equivalent (WME). The California Builder's Guide to Reducing Mold Risk suggests an upper limit of 16 percent WME for gypsum board before finishing or installing cabinets. This limit translates roughly to 0.9 percent moisture content by weight for gypsum board. Wood and wood products that contain a great deal of moisture should not be used in construction until their moisture content is below a certain percentage. Unfortunately, research on this dynamic is mostly confined to laboratory research and anecdotal reports from forensic cases. The California Builder's Guide to Reducing Mold Risk suggests an upper threshold of 19 percent moisture content for wooden materials. To avoid problems with shrinking or expansion, wood ideally should be installed at moisture content levels as close as possible to the average moisture content it will experience in service. The in-service moisture content of exterior wood depends on the outdoor relative humidity and exposure to rain and sun. The in-service moisture content of interior wood depends on the indoor relative humidity, which in turn is a function of moisture sources, ventilation rates and dehumidification. The in-service moisture content of exterior and interior wood depends on the climate in which the building is located and on the building's design and intended use. The U.S. Department of Agriculture's Wood Handbook recommends average moisture content of 15 percent or less, with maximum readings of 19 percent or less, to avoid dimensional change problems. The ability to measure material moisture content after construction is valuable for diagnosing post-construction problems such as water leaks, condensation and mold growth. It is recommended that builders and facility managers measure the moisture content of materials during post construction diagnosis and problem solving. A second moisture dynamic, the emission rate of water vapor from materials such as concrete floors, can have a dramatic impact on flooring materials. For example, floor covering manufacturers specify the maximum water vapor emission rate of concrete over which coverings such as tile and carpet can be installed. Installing a covering on concrete that exceeds the maximum emission rate may cause the covering to fail, promote mold growth and void the The moisture content of materials is usually expressed as the percentage of the weight of water in the material relative to the weight of the dry material. In laboratories, moisture content can be calculated C-1