Newly constructed buildings generally have higher humidity levels caused by the moisture inherent in building materials and processes. It is important to dry enclosed buildings out quickly to levels that will not support mold growth and to verify that acceptable levels have been reached and are maintained. Humidity should be monitored and controlled from the time the building is enclosed until all wet-finish materials have been applied and dried. Humidity controls are especially important in humid climates or when massive wet materials such as concrete or plaster are used. Inexpensive meters for determining temperature and relative humidity called thermohygrometers can be purchased at most electronics and hardware stores.
Relative humidity (RH) varies depending on temperature. Warmer air will have a lower RH than colder air with the same amount of water vapor. With a special chart called a psy – chrometric table, a trained consultant can convert readings from the thermohygrometer to determine the actual amount of water in the air or at surfaces at various temperatures. These figures are used to determine if a structure is dry enough. At 70 degrees Fahrenheit, mold will not grow at an RH level of under 60 percent measured at the surface. One way to measure the surface humidity is to affix the thermo hydrometer to the surface with a sheet of plastic sealed over it. After a few minutes the meter will stabilize and the RH can be read. If it is determined that humidity levels are too high, we recommend electric dehumidification. Note that if you can see condensation continuously on the windows for two days in a row, the building probably has areas that are wet enough to support microbial growth.
Certified water-loss technicians are trained and equipped to measure and dry buildings that have excessive levels of moisture. There are two associations that certify technicians and can help you locate qualified people in your vicinity. These are the Restoration Industry Association (RIA) and the Institute of Inspection, Cleaning and Restoration Certification (IICRC).
Calcium Chloride Moisture Testing
Large quantities of water are present in cement, gypsum concrete, aircrete, and other poured masonry materials. These materials must be adequately dried before finishes are applied. It is common in new construction for a carpet or other floor finish to be laid on a slab before the slab is thoroughly dry. Further drying is inhibited, allowing microbial spore levels to climb as mold growth invades these damp areas.
Kits for testing moisture in masonry are available (see Chart 13.1). They contain calcium chloride salts, which absorb moisture from the air at a known rate. A kit contains a plate that holds the calcium chloride salt, a plastic dome, and an adhesive material. Weigh the calcium chloride to the nearest hundredth of a gram. (You can find scales for weighing the salts at your local pharmacy.) Then place the calcium chloride test plate on the floor area to be tested and cover it with the plastic dome, which is sealed to the slab with the adhesive material. After 60 to 72 hours, remove the plastic dome and reweigh the calcium chloride. Based on the weight gain and the number of hours that have passed, you can determine the materials water vapor emissions rate. The kit instructions also contain a chart that will help you determine when the slab is dry enough for the application of various finishing materials. If a scale is unavailable, the sealed exposed kit can be shipped back to the manufacturer for weighing and calculations.