What the meters show
Dry to the Touch Is Not Dry
Here is a call the dispatch desk gets every week: a leak was fixed, the wall looks fine, but a tech puts a meter on it and it reads high. Painted drywall dries at the face while the gypsum core and the stud behind it stay wet. Close that up or hang a picture on it and you can end up with mold you will not see for weeks.
Drying techs set goals by reading the same material in a part of the house the water never touched. Only when the wet material matches that baseline is it considered dry, and not a day before.
Wood floors make the point just as clearly. With a slow leak under a dishwasher, the underside of the boards swells and the edges lift, which is called cupping. Sand it flat too early and it crowns once it dries. Drying mats and steady monitoring can often bring the boards back flat.
The physics in plain words: warm, dry air pulls moisture out of wet materials, and dehumidifiers pull it out of the air. Air movers keep the surface boundary layer moving so evaporation does not stall.
- Relative humidity tells you how saturated the air is at its current temperature
- GPP is the actual weight of water vapor in the air, which is the number techs track day to day
- Vapor pressure moves moisture from wetter materials toward drier air
- Dew point is where the air would condense on a cold surface, which matters on slabs and exterior walls