What the meters show
Why Dry to the Touch Does Not Mean Dry
A familiar story: the leak is repaired and the wall looks normal, yet the meter tells a different tale. Painted drywall dries at the face while the gypsum core and the stud behind it stay wet. Seal it up or push furniture against it, and mold can grow out of sight for weeks.
The drying target comes from what techs call the dry standard: readings taken on unaffected drywall, framing or flooring elsewhere in the house. 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. 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
- 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