Moisture Testing & Control
DryHero is often requested to assess moisture and water damage. We can test for hidden water trapped in building materials such as drywall, insulation, framing, attics, crawl spaces, concrete, wood flooring, cabinetry, subfloors, ceramic tile, showers, basement walls, carpet, pad, cushion and finish trim carpentry. Moisture inspections can help determine the extent of the water damage, verify if adequate drying was performed, and if there may be a mold risk or concern.
The true benefit of moisture testing is to determine WHY and HOW materials are getting wet. Numerous international studies have found health problems are much more common in damp and water damaged buildings. Musty odors and visible mold are often associated with dampness and water damage. Testing for water vapor in the air (humidity), in wall cavities and on surfaces may help determine what waterproofing remedies are required.
DryHero has robust inventory of penetrating and non-penetrating moisture meters as well as relative humidity data loggers and an infrared cameras. These include special moisture meters for Dry-Vit (EIFS).
Wood moisture content (WMC) is often used as an indicator of decay problems in houses. The moisture content of wooden substructure members may be disclosed in the closing process of real estate transactions. These WMC readings may be provided by pest control operators, home inspectors and restoration firms. Wide-spread and often extensive moisture damage occurs in residences across the state of Nebraska and elsewhere in the Midwest due to our warm, humid summer climate.
Wood Moisture Content is the weight of water in a piece of wood expressed as a percentage of oven dry weight of wood. Fresh cut trees can have a wood moisture content over 200%, while completely dried wood will have a wood moisture content of 0%. Wood in buildings usually has a wood moisture content of 5% to 15%.
WMC Scale’s Meanings:
Below 12% - Readings in this range are common to kiln or oven dried woods and furniture grades of wood, and represent dry conditions. Most interior wood is in this range.
12% - 16% - Readings in this range are common to lumber during construction, air dried lumber and “healthy” residential substructures (beneath first floor in crawl spaces). These are typical readings for exterior wood.
16% - 20% - Readings in this range indicate a possible elevated level of wood moisture. Such readings should alert the homeowner to look for a source of excess moisture. The excess moisture source should be corrected if found.
20% - 28% - Readings in this range indicate that conditions are border-line for decay. Surface molds may develop. The excess moisture source should be corrected immediately, and monitored until the WMC returns to the 12-16 range.
28% and above - Readings in this range are often accompanied by decay damage. Substructures with WMC in this range may show decay or rot in floor joist, sills, and subflooring. Repair is often required when WMC readings are in this range.
Wood moisture content between 0% and about 28% is dependent upon the relative humidity (RH) of the air. As the air’s RH increases, so does the moisture content of any wood exposed to the air. Wood exposed to air with a RH of about 90% will reach a Wood Moisture Content of about 20%. Above 90% RH or 20% WMC, mold can grow on the wood.
Decay fungi need liquid water to grow. Once wood is dried below about 28% WMC, water is not available to support decay, unless the wood is exposed to liquid water. This water may come from condensation, roof leaks, plumbing leaks, or contact with the soil. If decay or WMC readings over 28% are present, find and fix the sources of liquid water quickly.
WMC of framing members in a crawl space will usually be lowest in late winter and highest in late summer. If low WMC readings were obtained during the winter, and other signs of high moisture levels are present, obtain additional readings during the summer. Other signs of high moisture readings include surface mold, evidence of water flows in the crawl space or basement, evidence of water stains or evaporation from foundation walls and columns, evidence of condensation on ducts and evidence of water drops impacting the soil under ducts.
A wood’s Weight and Moisture Content
Wood is hygroscopic—meaning, when exposed to air, wood will lose or gain moisture until it is in equilibrium with the humidity and temperature of the air.
Moisture content (MC) from 5 to 25 percent may be determined using various moisture meters developed for this purpose. The most accurate method in all cases, and for any moisture content, is to follow the laboratory procedure of weighing the piece with moisture, removing the moisture by fully drying it in an oven (105 degrees C) and reweighing. The equation for determining moisture content is MC% = weight of wood with water - oven-dry weight / divided by oven-dry weight X 100.
Equilibrium Moisture Content
The moisture content of wood below the fiber saturation point is a function of both relative humidity and temperature in the surrounding air. When wood is neither gaining nor losing moisture, an equilibrium moisture content (EMC) has been reached.
Wood technologists have graphs that precisely tie EMC and relative humidity together, but as a rule of thumb, a relative humidity of 25 percent gives an EMC of 5 percent, and a relative humidity of 75 percent gives an EMC of 14 percent.
A 50 percent swing in relative humidity produces an EMC change of 10 percent. How that affects wood flooring depends on which species is being used. However, let’s say the width variation is just 1/16 inch for a 2 1/4-inch board. That’s a full inch over 16 boards in a floor. Over the width of a 10-foot wide floor, that amounts to more than three inches of total expansion or contraction.
Protective coatings cannot prevent wood from gaining or losing moisture; they merely slow the process.
The Seasoning of Lumber
Freshly sawn lumber begins to lose moisture immediately. Its color will darken and small splits or checks may occur. Movement of moisture continues at a rate determined by many factors, including temperature, humidity and air flow, until a point of equilibrium is reached with the surrounding air. The shrinking and swelling of wood are dimensional changes caused by loss or gain of water.