What the meters show
Why Dry to the Touch Does Not Mean 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. When the wet wall reads within range of that dry standard, it is dry; until then, the equipment keeps running.
Wood floors make the point just as clearly. After a slow leak under a sink or dishwasher, the bottom of the boards takes on water and swells, so the edges rise and the floor cups. 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 is how full the air is relative to what it can hold at that temperature
- GPP is the actual weight of water vapor in the air, which is the number techs track day to day
- Moisture moves from high vapor pressure in wet materials toward lower pressure in drier air
- Dew point tells the tech where condensation could form on cold slabs and outside walls