What the meters show
Dry to the Touch Is Not 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. Close that up or hang a picture on it and you can end up with mold you will not see 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. 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 patient monitoring often let the boards settle back down.
The short version: dry, warm air draws water out of materials, dehumidifiers remove it from the air, and air movers sweep the surface so evaporation keeps going.
- 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 tells the tech where condensation could form on cold slabs and outside walls