Measuring the level of moisture in gypsum board can be tricky.
Gypsum is a naturally occurring mineral that lends certain rock-like qualities to wallboard. Under extreme or sometimes even normal environmental conditions, gypsum board may become damp. It may also be intentionally moistened by drywall installers under controlled conditions in order to facilitate application of board to curved surfaces. Despite the possibility of encountering these conditions, gypsum board must not be repeatedly subjected to water, or prolonged high levels of moisture or dampness.
For many years, the manufacturers have cautioned that gypsum board should never be inundated by water, especially prior to application. This warning applies to the proper handling and protection of gypsum board when it is being shipped, stored, stocked or installed. Additionally, gypsum board and its systems must receive regular and routine maintenance following installation, especially in areas that may be exposed to periodic and unusually high moisture levels.